October 1992 y NREL/TP-257-4655

Combined Experiment Phase I 

Final Report 

C.P. Butterfield 

W.P. Musial 

D.A. Simms 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

A national laboratory of the U.S. Department of Energy 

Managed by Midwest Research Institute 

for the U.S. Department of Energy 

under contract No. DE-AC36-83CH10093 
NREL/TP-257-4655 • UC Category: 261 • DE92000012

Combined Experiment Phase I 

Final Report 

C.P. Butterfield 

W.P. Musial 

D.A. Simms 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

A national laboratory of the U.S. Department of Energy 

Managed by Midwest Research Institute 

for the U.S. Department of Energy 

under contract No. DE-AC36-83CH10093 

October 1992
NOTICE 

This report was prepared as an account of work sponsored by an agency of the United States 

government. Neither the United States government nor any agency thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents 

that its use would not infringe privately owned rights. Reference herein to any specific commercial 

product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily 

constitute or imply its endorsement, recommendation, or favoring by the United States government or any 

agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect 

those of the United States government or any agency thereof. 

TP-4655

1.0 Table of Contents

Acknowledgments ill

1.0 Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

2.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

3.0 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

4.0 Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4.1

4.2

4.3

Test Site .

Test Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MET Towers .

3

3

5

5.0 Instrumentation . 6

5.1 Pressure Measurements '. . . . 6

5.1.1 Pressure Taps 6

5.1.2 Pressure Transducer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5.1.3 Pressure System Controller '. . . . 8

5.1.4 Centrifugal Force Correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.2 Angle-of-Attack (AOA) Transducer . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.3 Strain Gages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5.4 Anemometers ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5.5 Video Equipment 19

5.5.1 Cameras... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5.5.2 Tufts.............................................. 19

5.5.3 Lighting............................................ 19

5.6 Miscellaneous Transducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

6.0 Data Acquisition and Reduction Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6.1 Combined Experiment PCM Systems 23

6.2 NREL PC-Based PCM Data Reduction System Hardware 26

6.2.1 Objectives of PC..PCM System Development 26

6.2.2 PC-PCM Decoding System Hardware 27

6.2.3 PC-PCM Decoding System Software 27

6.2.4 Data Flow in the Computer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

6.2.5 Data Capture Performance Estimates 29

6.2.6 Architecture of PCM Decoder Board 31

6.3 NREL PC-PCM Data Reduction System "Quick-Look" .

Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

6.3.1 Overview of the Quick-Look Program 33

iv
TP-4655

1.0 Table of Contents (continued)

603.2 Limitation of PC-Based Data Processing 34

6.3.3 Interfacing a PC to the PCM Data Streams . . . . . . . . . . . . . . . . . . . . 35

6.3.4 Contiguous Data Acquistion 36

6.3.5 Real-T1Dle Data Monitoring 36

6.3.6 Data Monitoring Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

6.3.7 Factors Affecting Data Monitor Rates 39

6.3.8 Data Base of PCM Stream Configuration. . . . . . . . . . . . . . . . . . . . . 40

6.3.9 Data Base of Channel Parameters 40

6.3.10 Derived Channel Data Base 41

6.3.11 Rapid Multi-Channel CalibrationCapability 41

6.3.12 Event Log File 42

6.3.13 Quick Review of RecordedData. . . . . . . . . . . . . . . . . . . . . . . . . . . 42

6.4 CombinedExperiment Data Processing 42

6.4.1 Measurement Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

6.4.2 Features of the Custom Data Calibration System . . . . . . . . . . 44

6.4.3 CombinedExperiment CalibrationSequences 45

6.4.4 Field Data Recording and Processing Requirements. . . . . . . . . . . . . .. 47

6.4.5 Comprehensive Data Postprocessing . . . . . . . . . . . . . . . . . . . . . . . . . 49

6.4.6 Dynamic Effects 50

7.0 Wind Tunnel Testing 52

7.1 DEIR Tunnel Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

7.2 Ohio State University (OSU) Wind Tunnel Tests 52

7.2.1 Steady Tests 53

7.2.2 Unsteady Aerodynamics Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

7.2.3 Rough Airfoil Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

7.3 Colorado State University Wind Tunnel. . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

7.3.1 Wind Tunnel Test Setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

7.3.2 Data Analysis 57

7.3.3 Wind Tunnel Results 57

8.0 Rough Airfoil Performance Tests . 60

8.1 Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

8.2 Roughness Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

8.3 Roughness Testing 62

8.4 Rough Performance Results 62

8.5 Rough S809 AirfoilCharacteristics 64

8.6 Wind Tunnel and RotatingComparisons of Rough Airfoil Data 68

9.0 References \ 72

v
·TP-4655

1.0 Table of Contents (con~luded)

Appendices

A. CombinedlUnsteady Aero Experiment High and Low Cal Setups for PCM 600 . . . . . . A-I

B. Unsteady Aero Experiment Measurement Tolerances B-1

C. Unsteady Aero Experiment Channel Data Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-l

D. Design and Experimental Results for the S809 Airfoil D-l

E. Wind Tunnel Tests ofthe S809 Airfoil Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-l

F. Integrated Coefficients from all Tests, Plots of Integrated

Coefficients D • D • • • F-l

G. Pressure Distributions for Reynolds number 650,000 Smooth G-l

H. Pressure Distributions for Reynolds number 650,000 Rough .........•......... H-l

I. Pressure Distributions for Reynolds number 500,000 Smooth 1-1

J. Pressure Distributions for Reynolds number 500,000 Rough J-l

K. Pressure Distributions for Reynolds number 300,000 Smooth K-l

L. Pressure Distributions for Reynolds number 300,000 Rough

vi

..':; . L-l
TP-4655

1.1 List of Figures

4-1 Test turbine description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4-2 Test turbine nacelle layout 4

4-3 Vertical plane array layout 5

5-1 Blade layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5-2 Typical pressure tap frequency response

(.065" In tube, 20" length) 7

5-3 Typical pressure-tap frequency content

(4% chord, 63% span) 8

5-4 Transducer installation in blade 9

5-5 Pressure system controllerblock diagram 10

5-6 Pressure system controller-pneumatic controls schematic . . . . . . . . . . . . . . . . . . . . .. 11

5-7 Local flow-angle transducer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13

5-8 Upwash effect and terminology 14

5-9 Wind tunnel calibrationof the local flow-angle sensor 15

5-10 Dynamic response test of the flow-angle sensor (Reynolds number=10') . . . . . . . . . .. 15

5-11 lift characteristics at deep stall 16

5-12 Instrumented blade strain gage - locations and bridge configurations 17

5-13 Vertical plane array layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . .. 18

6-1 CombinedexperimentPCM streams 22

6-2 Full PCM data reduction and processing 24

6-3 Data flow in the PC 30

6-4 Decoder board bit detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 32

6-5 Decoder board frame synchronizer 32

6-6 PC interface and control 33

6-7 Quick-look program data flow 38

6-8 Combined experiment phase II data processing plan . . . . . . . . . . . . . . . . . . . . . . . . .. 51

7-1 Wind tunnel data comparison. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 53

7-2 Colorado State University environmental wind tunnel. . . . . . . . . . . . . . . . . . . . . . . .. 55

7-3 Velocity profile of test section for CSU wind tunnel. . . . . . . . . . . . . . . . . . . . . . . . .. 56

7-4 Turbulence measurements in test section of CSU wind tunnel 56

7-5 Reynolds number effects on S809 airfoil and comparison airfoils. . . . . . . . . . . . . .. 58

7-6 lift and drag results for the S809 airfofl in the CSU wind tunnel. . . . . . . . . . . . . . . .. 59

8-1 60-kilowatt HAWT performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • .. 60

8-2 Roughness distribution on leading edges of test turbine blades. . . . . . . . . . . . . . . . . .. 62

8-3 Combined experiment wind turbine performance 63

8-4 Normalized power output-s-combined experiment '. . .. 64

8-5 S809 OSU wind tunnel data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 65

8-6 Comparison of rough and smooth CL data from rotating and

nonrotating airfoil tests .........................................•.... .66

vii
TP-4655

1.1 List of Figures (concluded)

8-7 0 Change in CL(mu) caused by NACA standard roughness and airfoil thickness

for typical wind turbine airfoils 67

8-8 LS(1)0413 smooth and rough airfoil performance 68

8-9 A comparison of pressure distributions for 110 angle of attack . . . . . . . . . . . . . . . . . .. 69

8-10 A comparison of pressure distributions for 140 angle of attack. . . . . . . . . . . . . . . . . .. 69

8-11 A comparison of pressure distributions for 180 angle of attack . . . . . . . . . . . . . . . . . .. 70

viii
TP-4655

1.2 List of Tables

Page

6-1 Combined ExperimentPCM Systems 25

6-2 Specifications for PC-PCM Decoder Board 27

6-3 Specifications for Analog Interface Module 27

6-4 User-Definable Options for the PC-PCM System 28

6-5 Quick-Look Program Features 34

6-6 Automatic Calibration Procedures 46

6-7 Manual Calibration Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 46

6-8 External Calibration Procedures 47

6-9 Event Acquisition Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 48 .

6-10 Six-monthExperimentAcquisition Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 48

ix
TP-4655

2.0 Introduction

Wind turbine operating experience has shown that current analysis techniques are inadequate when used

to predict peak power and loads on a fixed-pitch wind turbine. Vitema and Corrigan (1981) and TangIer

(1983) show evidence of higher-than-predicted power levels on staIl-controlled wind turbines. Because

performance and loads are the most important design information needed to achieve more reliable and

inexpensive wind turbines, it is important to understand the cause of the discrepancy. The primary

question is: How does the wind tunnel airfoil data differ from the airfoil performance on an operating

horizontal axis wind turbine (HAW1j? The National Renewable Energy Laboratory (NREL) has been

conducting a comprehensive test program focused on answering this question and understanding the basic

fluid mechanics of rotating HAWT stall aerodynamics.

The basic approach was to instrument a wind turbine rotor, using an airfoil that was well documented by

wind tunnel tests, and measure operating pressure distributions on the rotating blade. Based on the

integrated values of the pressure data, airfoil performance coefficients were obtained, and comparisons

were made between the rotating data and the wind tunnel data. Care was taken to minimize the

aerodynamic and geometric differences between the rotating and the wind tunnel models. Models were

made in the same molds, and the same instruments were used for both the rotating and wind tunnel cases.

This is the first oftwo reports describing the Combined Experiment Program and its results. This Phase I

report covers background information such as test setup and instrumentation. .It also includes wind tunnel

test results and roughness testing. The Phase II report concentrates on the aerodynamic pressure test

results. Average and unsteady aerodynamic measurements are presented. These reports were written for

two reasons: The first is to disseminate basic aerodynamic data that will be useful for code validation and

wind turbine design information. The second is to provide a current orientation for researchers using the

data or participating in the Combined Experiment Program. These reports provide a comprehensive

description of results to date and a description of how the experiment operates.

'.

1
TP-4655

3.0 Background

The Combined Experiment was planned and carried out over a period of four years. It was the most

comprehensive wind turbine test program ever attempted, with more than 200 signals simultaneously

measured and recorded. The test program was divided into two phases: Phase I planning began in spring

1987. Phase II began following the completion of the Phase I tests in spring 1989. Many configurations

ofinstrumentation were considered during each phase of testing as lessons were learned and instruments

were improved. Although the instruments were continually upgraded, the major configuration change

. between Phase I and Phase II was the extent of the pressure measurements. The instrumented blade for

Phase I had only one span-wise radial station of pressure taps (32 taps) at 80% radius, but the Phase II

blade had four radial stations of pressure taps at radial positions ranging from 30% radius to 80% as well

as six intermediate radial stations oftaps located between the primary stations. A new instrumented blade

was fabricated for both Phases I and II. The major instrumentation configuration changes that were made

between Phases I and II were as follows:

• A thermal drift problem in the Phase I strain gages was corrected with more careful matching of

the gage and blade thermal expansion properties. .

• A second root-mounted video camera was added to the instrumented blade for Phase II and was

pointed toward the tip of the blade. This camera could view the entire blade from one position.

• The R. M. Young U-V-W fixed-axis anemometers on the vertical plane array (VPA), in Phase I,

were replaced by prop-vane anemometers.

• Two bi-vane anemometers were added at hub height on the north and south sides of the VPA.

• The sonic anemometer and thehot-film anemometers on the local meteorological tower were not

operating during Phase II.

• In Phase II, a Honeywell 16-channel tape recorder replaced a Sabre-80 14-channel tape recorder.

The Honeywell recorder had a higher bandwidth than the Sabre and allowed the tape to be played

slower; therefore, more data per tape were recorded.

Phase I testing was conducted between July 1988 and May 1989. Many of the fifty-five 30-min analog

tapes that were recorded were not usable because of various instrumentation problems, but there were

enough good-quality records to establish a baseline data set The Phase I tests were necessary to refine

·the details of the instrumentation and data acquisition system to gain a preliminary understanding of how

to interpret the pressure measurements and process the data. The Phase I report will cover the test setup.

instrumentation, wind tunnel tests, and airfoil roughness testing. Much of the Phase II success can be

attributed to the Phase I experience.

Most of the datapresented came from the more comprehensive Phase II datasets and will be presented

in the Phase II report This report will cover the wind turbine test results, including:

• Bin averaged aerodynamic coefficients dataintegrated from pressure distributions

• Bin averaged blade load data

• Unsteady aerodynamic data.

2
TP-4655

4.0 Test Setup

4.1 Test Site

The test site where all the atmospheric testing was conducted is located at the NREL Wind Energy Test

Center at the Rocky Flats Plant 10 miles north of Golden, Colorado. Winter winds are dominant at this

site from a prevailing direction of 292 deg. Thelocal terrainis flat" withgrassyvegetation extending over

.1/2' mile upwind. However, the site sits only a few miles from the opening of Eldorado Canyon at the

base of theRocky Mountains, which are located directly upwind. The wind turbinewas unobstructed by

other structures or wind turbines. A layout of the wind site and test turbine is given in Simms and

Butterfield (1990).

4.2 Test Turbine

TheCombined Experiment TestTurbinewas a modified Grumman WindStream33. It was a 10-m-diam.,

three-bladed, downwind, free-yaw turbine equipped with full span pitch capability that is manually

controlled during the testing to provide fixed-pitch (stall-eontrolled) operation at any pitch angle desired.

The rotational speed of the rotor was a constant72 RPM. The turbine was supported on a guyed-pole

tower. It was equipped with a hingedbase and gin pole to allowit to be tilted down easily. An electric

winchwas used to lower and raise the system duringinstallation. A base-controlled yaw lock was added

to allowlocked yaw operation at arbitrary yawpositions from the ground 'This yawretentionsystemhad

a strain-gaged link to measure yaw moments. Also added was a mechanical caliper brake'system that

could be operatedmanually from the control shed The specifications for this wind turbine are shownin

Figure 4-1. A schematic of the turbine's nacelle is shown in Figure 4-2.

10 Meter diameter

20 Kilowatt

72 RPM

Constant chord

Zero twist

5809 airfoil

. Pitch control

Down wind

Camera boom

'Ughts

-Test blade

Angle of attack probe -~~-l-l

Total pressure probe ---lI--t-----,

Tower--

Figure 4-1. Test turbine description

3
TP-4655

1 - Generator

2 - Disc brake

3 • H.S. shaft

4 - Pitch cont actuator

5· Swivel

6· Gearbox

7 - Pillow block bearing

8· Cowling

9 - Rotor shaft

10 • Fig block bearing

11 - Tlirust bearing

12 - Vertical shaft

13 - Tower

14 • Strongback

15 - Torque link

16 - Redundant pitch cont actuator

17 - Redundant pitch actuator crank

Figure 4-2. Test turbine nacelle layout

The new blade was the most significant configuration change. The original .blade platform was

maintained, but the NREL S809 airfoil replaced the original Grumman airfoil. The S809 airfoil was

developed by Airfoils, Inc., under contract to NREL (Simms and Butterfield, 1990). The primary reason

this airfoil was chosen was that it had a well-documented wind tunnel data base that includes pressure

distributions, separation boundary locations, drag data, and flow-visualization data.

The blades had a constant .45-m (I8-in.) chord with zero twist. The blade material was a fiberglass/epoxy

composite. The blades were designed to be stiff to limit aero-elastic blade deflections. The dynamic

characteristics of the blade were tailored to avoid coalescence of rotor harmonics with flap-wise, edgewise, and torsional natural frequencies. To minimize the possibility of aero-elastic instabilities, the mass

and elastic axes were aligned with the aerodynamic axis. The instrumented blade was painted black to

contrast with the white tufts that were used for flow visualization.

Some of the advantages of this turbine were:

• The rigid, three-bladed rotor reduced the amount of out-of-plane blade motion and minimized

aero-elastic effects.

4
TP-4655

• The constant-chord, zero-twist blade reduced the effects of blade geometry on stalled flow.

• The downwind rotor configuration allowed a boom-mounted camera to view tufts on the lowpress,ure side of the blade withoutobstructions.

• The simplicity, small size, and high availability of parts made test modifications such as tower

tilting, transducer mounting, and control system changes easy and inexpensive.

." - The manual pitch control system allowed stall-controlled operation at any pitch angle.

4.3 MET Towers

The north:MET tower or far-field :MET tower was 50 m tall and waslocated500 m upwindfrom the test

turbine. Instruments mounted on this tower were used to measure the large-scale atmospheric conditions

ofthe inflow.

For local inflow measurements, two Rohn 45-0 guyed MET towers were erected directlyupwind of the

test machine in the prevailing wind direction. The two towers supported three cross-booms, where

13 anemometers in a VPA were mounted to measure the inflow in the near field The VPA was

positioned one rotor diameter (ID) upwind of the turbine.

A 55-ft local MET tower was locatedto the north of the VPA ID upwind Mounted on it were the highfrequency atmospheric instruments. Figure4-3 showsthe placement of the VPA andthe local METtower

with respect to the turbine location. The specifics of the anemometry are discussed in Section5.4.

"Hub height

(55 ft)

Item No. Description"

1 U-V-Wsonic anemometer

2 Ruggedized hot films

3 Bi vane anemometers

4 Propvane anemometers

1/80

Local Met

Tower

Quantity

1

2

2

13

Figure 4-3. Vertical plane array layout

5
TP-4655

5.0 Instrumentation

5.1 Pressure Measurements

5.1.1 Pressure Taps

Blade surface pressures were the most important and the most difficult measurements to make. The

accuracy of the aerodynamic performance coefficients was dependent on the individual pressure tap

measurements because each coefficient is the integrated value of the measured pressure distribution at that

radial station. The measurement approach was to install small pressure taps in the surface of the blade

skin. Each opening was mounted flush to the airfoil surface and was 0.040 in. in diameter. The flush

profile was necessary to prevent the taps themselves from disturbing the flow. Stainless steel tubes, each

less than 0.5 m in length, were installed inside the blade's skin during manufacturing to carry surface

pressures to the pressure transducer. For Phase I testing, 32 ressure taps were located at 80% of full

blade span, where the Reynolds number is approximately 10. In Phase II, three more stations were

added: one at 63%R, one at 47%R, and one at 30%R. The taps were aligned along the chord (instead of

being staggered) so that span-wise variations in pressure distributions would not distort measured"chordwise distributions. The chord-wise spacing of the pressure taps is shown in Figure 5-1.

<:-~.' ,~l I " ! ! , ! ! , ! ! I I

o 10 20 30 40 50 60 70 80 90 100

% Chord (18-in. chord)

100

90

eo

70

~60

.5

50

..

.g

C2 40

30

20

10

o

----- Indicates fun distribution

of taps

---- Indicates 4%

and 36%

taps only

Figure 5-1. Blade layout

6
TP-4655

The tube lengths were minimized to avoid dynamic effects between the surface of the blade and the

transducer. Pressure tap tube acoustical frequency response limits accurate pressure measurements to 20%

of the first harmonic frequency. In the case of a 45-cm-Iong (I8-in.) tube, the first harmonic is

approximately 80 Hz according to Irwin, Cooper, and Hirard (1979). They describe how this can be

corrected in software by measuring the acoustical transfer function ofthe tube and applying the measured

transfer function to the data in the frequency domain. A recursive filter can also be used to apply the

transfer function to the data in the time domain. This technique is used to get a full lOO-Hz bandwidth

from the pressure signals.

Transfer functions were measured between applied surface pressures and pressures measured by the

transducer (Akins, 1987). Figure 5-2 shows that for a 100in. stainless steel tube, only minimal distortion

occurs below SO Hz, but the most significant amplification occurs between SO to 100Hz. A typical

spectral density plot for the 4% chord pressure tap at the 63% radial station is shown in Figure 5-3. The

dynamic response of the pressure system shows the absence of significant spectral energy above 50 Hz,

which indicates that the dynamic effects can be ignored Based on these data, dynamic corrections were

not made to the pressure measurements,

2.0

co

lB

1.0J---------~~::o=:="=-=~:-=::'= --------------

------------------------~-----

100

Frequency (Hz) 100

Frequency (Hz) .

-0>

Q)

Q)

C>

c 0 en

Q)

gJ L-------==================-_L__.J .c 180

a.. 0

Q)

o . c

Q)

.!:

o

o

1.0t=------------- _

100 Frequency (Hz)

O.O------------------ .....J

o

Figure 5-2. Typical pressure tap frequency response

(.065" ID tube, 20'1 length)

7
TP-4655

102

101

E

::J

...

ts

Q) 10 eli)

E

Q)

·u 10-1 !i:

Q)

8

::J 10-2 II)

II)

Q)

...

0.

1.0 10.0 100.0

Frequency (Hz)

Figure 5-3. Typical pressure tap frequency content

(4% chord, 63% span)

5.1.2 Pressure Transducer

The specifications of this test program required pressure measurements within 2% to 3% of the local

dynamic pressure with a bandwidth of 100 Hz. This corresponded to an accuracy of 137 micro-bars

(0.002 psi) at the 80% blade span and 11 micro-bars (0.0002 psi) at the inboard30%Rblade station. To

obtain this accuracy. it was necessary to conductfrequent range and zero calibrations during the test.

Pressure Systems International Model ESP-32 pressure transducers were used. They are electronic

scanner-type transducers thatprovide remote calibration capability throughapneumatically operated valve.

The transducers were installedinside the blade as close to the pressure taps as possible. One transducer

wasused at each32-tapspan-wise station. Figure5-4 is a diagram showing the installation of the pressure

transducers and pressure taps within the blade.

5.1.3 Pressure System Controller (PSC)

Remote control of calibration, scanner addressing, and demultiplexing of the analog multiplexed signal

wereperformed by the PSC. ThePSC was a hub-mounted microprocessor control unit Figure 5-5 shows

a block diagram of the PSC designed by NREL. The PSC was designed to controland process datafrom

four ESP-32 transducers in parallel and is capable of processing as many as 128 pressure channels

simultaneously withoutanyloss in performance. A minimum frequency response of 100Hz wasrequired

to studydynamic stall behavior on the rotating windturbineblade. To accomplish this, the pressure port

address wasincremented fromport-to-port at 16,646 Hz,resulting in complete scans of all pressure ports

on each PCM stream at 520 Hz and a port-to-port settling timeof 60 usee, Thesesamples werepassed

8
1 mm 10

stainlessySkin .

D-spar

800/0 span -.-.'"

Pressure

transducer

D-spar

access port Skin

C')

o

CD

on

o

C')

e

.(

a:I

TP-4655

Figure 5-4. Transducer installation In blade

on to the PSC as analog multiplexed signals where they were digitized, distributed to 32 digital-to-analog

(DIA) converters on a digital bus, and passed through individual reconstruction filters, The filters were

tOO-Hz precision, four-pole Butterworth filters. Each of the reconstructed analog output signals, one for

each channel, was passed to the pulse code modulation (PCM) encoder. The output of the PCM system

was passed over slip.rings to the control building and was recorded on a wide-band tape recorder for later

processing.

Although the processing from analog to digital and then back to digital was cumbersome, it provided

flexibility and was very stable. When the system was designed, a frequency multiplexing system was to

be used for data recording. 'This system would have required analog output

A schematic ofthe pneumatic valve controls is shown in Figure 5-6. There are six independent pneumatic

control valves in the PSC that are electronically controlled by the PSC. A O.094-~3 (l-ff) dry nitrogen

control pressure reservoir supplies pneumatic control pressure at 80 psi to operate the pressure transducer

functions.

A ramp calibration sequence is started by energizing a set of pneumatic valves in the controller. Control .

pressure is sent out the blade to the "purge valve" and shuttles a plate that connects all pressure input ports

to a common calibration pressure line and connects all surface pressure tap tubes to a common purge

pressure line. When the calibration command is given from the test shed, calibration pressure is

simultaneously applied to all the taps in step-wise increments by a motorized syringe under microprocessor

control. Calibration pressure is measured by a Setra 237 differential pressure transducer mounted in the

PSC. The syringe provided.a means of accurately 'applying small positive and negative pressures to the

ESP-32 transducers.

9


TP-4655

If desired, a "purge" command could be given. For this option, a set of valves is energized that sends

controlpressureto a pneumatically controlled purge valve that is mountednext to the ESP-32. When the

purge valve receives control pressure, all the pressure taps are connected to a regulated supply of dry

nitrogen at 5 psi that is exhaustedout all the pressure tap tubes to clear moistureor debris. This feature

was exercised before each test to assure that no blockages were present.

Zero calibration was accomplished by energizing a different set of valves that send pneumatic control

pressure out the blade to the ESP-32 transducer, which connects all input pressures to the reference

pressure line. Zero calibrations were initiated every 5 min of testing to track zero drift on all channels.

5.1.4 Centrifugal Force Correction

Establishing a referencepressure for each transducer was non-trivial for transducers located in a rotating

environment. The air pressures inside the rotating blade were unpredictable and rapidly fluctuating, so

it was not possibleto establish a reference pressure at the transducer. Instead, the reference tap of each

ESP-32 transducer was connected to a single reference pressure line that was terminated at the hubmounted PSC. This created another problem. Centrifugal forces acting on the column of air in the

reference tube change the pressure along the radius of the wind turbine rotor. The actual reference

pressure experienced by the transducers was calculatedby using the following equation:

(5-1)

where:

Patm =atmospheric pressure

Pcf =pressure due to centrifugal force

r =radial distance to transducer

n = rotor speed

p = air density.

Tests were run to verify the accuracy of Eq. 5-1 and confirmed the predicted values to within the

measurement accuracy of the transducer.

5.2 Angle-ot-Attack (AOA) Transducer

The main objective of this test programwas to comparewindtunneldata with rotating blade data. Before

this could be done, an accurate means of measuring and comparing the ADA on a rotating blade was

needed. Geometric ADA measurements are fairly easy to make in a wind tunnel where the air flow is

precisely controlled, but on rotor they are much more difficult. To accomplish this, it was necessary to

make measurements of the local inflow in front of the blade.

Figure 5-7 shows the flow angle sensor (FAS) that was developed by NREL for this test program.

Lenschow (1971)describes earlydevelopment andtestingof a similarsensorthat was usedin atmospheric

flight testing. The CombinedExperimentFAS used a small,lightweight rigid flag that aligneditself with

the local flow. The flag angleis measured with a commercial rotary positionsensor mountedin a custom

housing. The analog signals generated were sent to the hub, multiplexed, and recorded with the other

signals by the dataacquisition system. Flag angles were measured within O.I-deg accuracy. The sensor

was mounted36 cm aheadof the leadingedgeon 5/8-in.-diam. carbontubes. Transducers werepositioned .

12
TP-4655

Total pressure probe

Row angle sensor

Figure 5-7. Local flow-angle transducer

6% outboard of each pressure station in order to limit flow disturbances on the blade near the pressure

taps. A total pressure probe was mounted at the tip of each sensor to record the dynamic pressure, Q.

There were two areas of concern regarding the accuracy of this FAS. FIrSt, local upwash effects and

induced velocities created by rotor wake expansions distort the flow around the airfoil. Figure 5-8 shows

typical streamlines under the influence of circulation-induced upwash. This effect causes the FAS to

measure a different flow angle than the geometric AOA, which is based on free stream flow. The second

potential for error was the dynamic response characteristics of the sensor's flag. To investigate these

issues, the sensor and probe were mounted on the wind tunnel model during tunnel testing. The effects

of upwash, frequency response, and Reynolds number were determined. A steady-state and a dynamic

correction were developed for the measured local flow angles (LFAs) using a combination of analytical

and experimental techniques to accurately determine the true ADA.

Figure 5-9 shows the results ofsteady tests. The dashed line in represents a zero correction reference line

or a condition where the FAS would measure the same angle as the geometric model angle during the

wind tunnel testing. Triangles show data measured by the FAS with a solid line curve fit to these data.

As can be seen, the upwash effect is important At a geometric angle of 10 deg, the FAS indicates a

14-deg angle. The 4-deg discrepancy is due to the net effect of bound circulation and wake-induced flow.

The solid line shows a prediction of the upwash effect. The Kutta-Joukowski Theorem was used to

estimate the bound circulation, and the Biot-Savart Law was used to determine the local induced velocity.

The vector sum of induced velocity-the resultant inflow velocity-was taken to determine the corrected

flow angle. The agreement is reasonable at low angles where the flow is attached to the airfoil, but as

the angle increases and the flow separates the agreement gets worse. Reynolds number effects were

estimated to be insignificant for the steady-state wind tunnel tests. The measured wind tunnel data

correction was used as the steady correction for the field test data analysis in this report. The details of

this correction are presented by Gregorek, Hoffmann, and Mulh (1991).

13
TP-4655

To determine the dynamic response of the FAS, the flag was deflected and released in the wind tunnel

at various Reynolds numbers. By recording the decay of the oscillations, a second-order system natural

frequency and logarithmic damping ratio were determined. Figure 5-10 shows the angular displacement

of the flag as the oscillations decay. Also shown are the analytical approximations for each case. From

the comparisons, it is clear that the FAS,is 'well damped but not critically damped, and the second-order

differential equations model the response well.

There is at least one caution that should be recognized pertaining to the above discussion. It is possible

that dynamic bound circulation changes could cause local flow field modifications that would. alter the

steady correction shown in Figure 5-9. These effects are unknown at this time. Future dynamic stall wind

tunnel tests will attempt to address this issue. To investigate this, the FAS will be mounted on a wind

tunnel model in the tunnel while the model ADA is oscillated at representative frequencies. The effect

of the dynamic flow field on upwash will be reflected in a comparison between geometric ADA and

measured LFA.

Pressure Distributions

Integrated Forces

a • Geometric angle-of-attack

9 - a + localinduced velocity effect

CL • Uft coefficient

Co. Drag coefficient

CN • Normal forcecoefficient

CT· Tangent Force Coefficient

Cm • Pitching moment coefficient

Figure 5-8. Upwash effectandterminology

14

TP4655

The reader should note that LFA data are not corrected for either FAS dynamic characteristics or dynamic

flow field effects. However, the FAS dynamic effects are estimated to be minimal for AOA variations

less than 2 Hz because the sensor's natural frequency is approximately 10 Hz, or 8.3 times the rotational

frequency, Also, the data are block averaged from 522 Hz to 10 Hz. This averaging should reduce the

scatter because of FAS dynamics. Another observation that supports the assumption that dynamically

induced errors in AOA measurements are small is shown in Figure 5-11. This shows that data scatter is

relatively small for low to moderate LFAs. Ifthe dynamic effects mentioned above were playing a large

role, significant scatter would be expected throughout the entire range of LFA, but scatter is large only

at high LFAs where stall is present These results are discussed in more detail later in this report and also

by Butterfield (1989). The data shown in Figure 5-11 were block averaged from 522 Hz to 10 Hz. This

figure represents five minutes of time during yawed operation.

"l

0

co

0

<.0

,0

--(l)

o~

U6

4-'

--,- "l -I .

0

0

0

"l

0

I

0

1-5 0

o o

o

c

o

o

o 0

Delft Wind Tunnel

'" to to to .. OSU Wind Tunnel

00000 Rotating Blade (GS208A)

5 10 15 20 25 30 35 40 45

Local Flow Angle (deg)

Figure 5-11. Lift characteristics at deep stall

5.3 Strain Gages

Strain gages were used to measure blade, tower, rotor, and yaw loads. Blade flap-wise and edge-wise

loads were monitored at eight span-wise locations along the instrumented blade. Pitching moment (i.e.,

blade torsion) was monitored at three span-wise locations. Figure 5-12 shows the locations of all the

blade strain gages. Load measurements were taken to help establish reliable blade load distributions to

help us validate the measured aerodynamic pressure measurements.

Each strain gage bridge was made up of four active gage elements mounted inside the fiberglass blade

skin. The gages were installed inside the skin during the blade manufacturing process to preserve the

exterior airfoil shape and surface smoothness. The strain gages were positioned carefully to minimize

flap-wise and edge-wise cross-talk. A maximum of 4% cross-talk was measured during the blade pull

16

TP-4655

and strain gage calibration tests. These cross-channel interference effects were not considered significant,

and corrections were not applied to the data

5.4 Anemometers

A variety of anemometers was used during this testing. ' The primary near-field data were obtained from

anemometers mounted on the VPA and the near-field .METtower. Far-field atmospheric stability data

were provided at the test site's 50-m north.MET tower.

A .80 ring of eight R. M. Young prop-vane anemometers was mounted on the VPA; they were the

primary measure oflocal wind speed and direction. The anemometers were evenly spaced around the ring,

which was centered 10 directly upwind at hub height A 040 inner ring of R. M. Young three-axis prop

anemometers provided low-frequency (0-1 Hz) wind-shear data, azimuthally varying wind data, and lowfrequency inflow statistics during Phase I testing. The inner ring was concentric with the outer ring. A

single R. M. Young prop vane was positioned at hub height in the center of the two rings. For Phase II

testing, the inner ring of U-V-W prop vane anemometers was replaced by four prop vanes to make the

wind-speed measurements more comparable. Two bi-vanes were also added for Phase II to provide a

measurement of the vertical component of the wind. These were spaced 10 apart and centered on the

VPA at hub height

High-frequency (0-10 Hz) data were provided by a Kajieo Denki three-axis sonic anemometer mounted

at hub height on the near-field MET tower and two TSI X-type dual-axis hot-wire anemometers mounted

1.2 m below hub height The X-films provide measurements of horizontal and vertical wind velocity

components at relatively high frequencies. An elevation view of the near-field anemometry is shown in

Figure 5-13.

Vertical Plane Array

Hub height

(55 ft)

20

(66 ft)

1/80

Local Met

Tower

Item No. Description ·

1 U-V-W sonic anemometer

2 Ruggedized hot films

3 Bi vane anemometers

4 Prop vane anemometers

Quantity

1

2

2

13

Figure 5-13. Vertical plane array layout

18
TP-4655

Far-field atmospheric data were recorded from the north MET tower. These data included temperature

gradient, wind shear up to 50 m, relative humidity, and wind directions at four different altitudes. These

data combined allowed measurements of atmospheric stability (Richardson number) to be made. These

data were multiplexed near the tower base and telemetered to the Combined Experiment test shed where

they were recorded.

5.5 Video Equipment

5.5.1 Cameras

A lightweight 10-ft boom was designed and mounted to the hub to hold the 10-lb, high-shutter-speed

video camera. The boom and camera arrangement was designed to be stiff with a system fundamental

frequency of 10 cycles per revolution (lOP), and the axes of the boom and camera were mass balanced

about the axis of rotation. The lo-ft boom length allowed a view angle of 30 deg at the tip of the blade

and 45 deg at the 66% span. Additional equipment, such as the data acquisition system, the PSC, and

lighting for night testing were also mounted on the boom.

For Phase I testing, a NISUS N-2000 video camera was used. A video monitor and recorder in the test

shed were used to observe tufts on the low-pressure side of the blade. The camera used a mechanical

shutter to freeze video frames in 1/625 of a second. Thirty video frames were recorded every second to

allow one frame to berecorded for every 11 deg of rotor azimuth position. The horizontal resolution of

this system is limited to approximately 250 lines. One problem with this system was that good angular

measurements ofthe tufts were difficult to interpret from the video images. For Phase II, the entire video

system was upgraded to improve the images ofthe tufts. The boom-mounted NISUS camera was replaced

by acolorPanasonic model WV-CL300. A second camera, aPanasonic WV-BD400 with a 15 to 160 rom

Rainbow G10X16ME zoom lens, was also added to provide another independent view angle along the

blade span. 'This camera was mounted on the blade itself and was allowed to pitch with the blade. This

view provided a full span picture of all the tufts at one time and was instrumental in helping to identify

and match flow patterns with the aerodynamic phenomena observed in the data.

5.5.2 Tufts

Tufts were attached to the surface of the instrumented blade to allow the air flow over the blade to be

visualized. The tufts were made of thin, white, polyester thread measuring approximately 0.25 mm in

diameter and 45 rom in length. They were attached to the downwind side of the blade with a small drop

of fast drying glue. Tufts were placed in rows spaced 76 rom (3 in.) apart in the blade span-wise

direction. In each row, the tufts were spaced one every 10% ofthe chord. The tufts on the leading edge

and at 10% chord were intentionally omitted to avoid blade roughness effects that might have been created

by the tufts themselves. The diameter of the tufts was chosen to minimize the effects on the boundary

layer yet maintain good visibility for the video camera. If the tufts were large relative to the boundary

layer thickness, they could cause transition or premature separation. This effect is discussed in more detail

by Rae and Pope (1984).

5.5.3 Lighting

Night testing was generally preferred over daytime tests. The black coloring of the blade that was chosen

to enhance the contrast of the tufts caused differential heating of the blade surfaces during the day. This

led to a thermal drift problem with the blade strain gages. Also, daylight tended to produce a large

amount of glare and reflections that interfered with the video images. Night testing required lighting to

be added to illuminate the white tufts. Eleven tungsten-halogen 120-V spotlights were placed along the

camera boom and directed at the blade. With this configuration, the video pixel intensity of.a tuft was

19
TP-4655

35 on a gray scale of 0 to 256, and the black background was 10 to 15; the contrast was great enough so

that the tufts couId be seen easily. Unfortunately, there was still not enough light to operate the camera

shutter, and moving images were blurred on the video display. In Phase II, the camera resolution was

greatly improved, and remote control of the iris and focus adjustments were added.

5.6 Miscellaneous Transducers

In addition to the extensive hub-mounted instrumentation, several other measurements were required to

complete the investigation of this turbine. Strain gages were mounted on the main shaft of the turbine

to measure rotor torque and main shaft bending on two axes. Tower bending gages were mounted on two

tower bending axes at the point just above the guy wire attachment These gages were oriented to

measure bending in the direction of the prevailing wind and orthogonal to the prevailing wind Gages

were mounted on the arm of the yaw brake to allow the measurement of yaw moment when the yaw brake

was engaged. Special sensors were developed to measure yaw position (gear-driven potentiometer), pitch

angle (gear-driven potentiometer), and rotor azimuth position (Trump Ross 512pulselrevolution

incremental encoder). Generator power was monitored using an Ohio Semitronics, Inc. (OSI) transducer

in the test shed.

20
TP-4655

6.0 Data Acquisition and Reduction Systems

To accomplish the objectives of theCombined Experimentrequirescollecting datafrom three majorareas:

turbine rotating, turbine non-rotating, and meteorological. In the rotating turbine frame, measurements

are made on the turbine blades, blade attachments, and hub. Typical parameters include strain gage

bending moments andtorsion,airfoilsurfacepressuredistributions, totaldynamic pressure, andbladepitch

angle. Thesemeasurements providedata to determine blade aerodynamic and structural loads. In the nonrotatingturbineframe, measurements characterize machine performance anddetermine turbineloads. This

requires data from the turbine nacelle and tower, such as generator power production; tower bending,

azimuth and yaw angles, and rotation speed.

To determine characteristics of the wind at the turbine, meteorological conditions are measured.

Anemometers are used to measure near-field horizontal and vertical wind shear. This requires many

channels of wind-speed and wind-direction data from local upwind anemometer arrays. Atmospheric

stability measurements are also important in evaluating inflow characteristics. This requires far-field

atmospheric boundary layer measurements, includinganemometry, temperature, barometric pressure, and

dew point

In an effort to increase accuracy, simplify instrumentation, and reduce noise, analog data signals are

sampled and encoded into digital PCM streams as close to the measurement source as possible. The

streams are then telemeteredto a convenient centralreceiving location and recorded on multi-track tape.

Streams are conducted throughslip rings and cablesor transmitted over a radio frequency (RF) link. PCM

stream layouts for the Combined Experiment are shown in Figure 6-1 and describedin Section 6.1.

The Combined Experimentuses a customized digital PCM-based hardware system for data acquisition.

The system was developed and is used for the following reasons:

• To provide required measurement bandwidth and accuracy, especially from pressure measurements

on the rotating blade, and to minimize induced noise and electronic drift in rugged and harsh

environments

• To perform automated multi-channel calibrations that enable essential rapid data verification in the

field

• To generate all required ancillary parameters, provide uncertainty analyses, and allow complete

comprehensive data postprocessing.

The system accomplishes these objectives by incorporating military-spec PCM encoders that digitize

analog signals close to the measurement source and transmit information in digital format to the ground.

The system also has built-in microprocessor-controlled calibrationcapabilities and prescribedcalibration

techniques that were designed to ensure data accuracy.

NREL developed a low-cost PC-based PCM decoding system specifically for use in the Combined

Experiment to facilitate quick PCM data analysis. We were severely limited in our ability to decode

multiple PCM streams for quick-look data processing and display in the field. There were no costeffectivecommercial systemsavailable thatprovidedthe requiredcapabilities. We neededmultiple-stream

decoding, derivation of parameters from multiple channels (across PCM streams), graphic display, data

storage, and a means to rapidly update calibration coefficients. We also needed the ability to monitor

long-termmeteorological conditions for evaluating currentteststatus. Thesefieldcapabilities are essential

21

TP-4655

because debugging using laboratory-based postprocessing is inefficient and impractical. We therefore

developed PC-bas~ PCMdecoding hardware (Simms andButterfield, 1990) and wrotea custom"QuickLook" PCM data management software program (Simms, 1990). These are described in Sections 6.2

and 6.3.

After initial field-based verification, PCM data streams from the Combined Experiment recorded on

wide-band tape are extensively postprocessed in the laboratory. Many phases of comprehensive number

crunching are necessary to producethe final required data sets to prescribed accuracy limits. These are

described in Section 6.4. The basic processes involved are as follows:

• Use the PC-based Quick-Look system to produce valid calibration coefficients for all measured

channels.

• Use a custom laboratory-based telemetry data reduction system called the EXPRT PCM

Decommutation System(Fairchild Weston, 1985) to merge the PCM streaminto a continuous time

series.

• Use ·various UNIX-based computer systems and custom software to perform engineering. unit

conversions, deriveancillary parameters, generate spectra, provide digitalfiltering, generate statistics,

and maintain a data base of all data records.

The data postprocessing path is shownin Figure 6-2. Along the way, there are also many data integrity

checks. Final data records contain 239 channels at 520 samples per second. They are stored in 5-minlong engineering unit records, each requiring 150 Mbytes of disk storage space. We use an erasable

optical disk system and a PC-baseddatabase programto managethe current5-h, 18-Gbyte data set We

have also developed a digital data processing systemto filter datasets from l00-Hz to 40-, 10-, and I-Hz

bandwidth and generatepower spectrain various frequency ranges. These are usedto ensuredata quality

and facilitate subsequent data analyses.

6.1 Combined Experiment PCM Systems

PCM-encoded telemetry data systems provide highly accurate measurements over a wide dynamic range

with low noise (Strock, 1983). These systems are ideal for collecting data related to the study of wind

turbines, especially in theCombined Experiment, whichrequires accurate multiple-channel measurements

taken from a variety of different locations. PCM systems consistof two basic components:

• Encoders to convertincoming analog signals into digital PCM values

• Decoders to decommutate the PCM valuesinto data that can be computer processed.

Six PCM streams are used for datacollection. Three streams are recordedin the rotating frame, two from

local inflowand the turbine/tower, and one from far-field meteorology. Characteristics of the streams are

summarized in Table 6-1.

23

TP-4655

Table 6-1. Combined Experiment PCM Systems

Bit Sample Number Sample PCM

PCM rate rate of interval source

# (Kbitls) (Hz) channels (msec) location

1 7.5 34.72 16 28.8 Far MET

2 15 69.44 16 14.4 Inflow

3 60 277.78 16 3.6 InflowfTurbine

4 400 520.83 62 1.92 Rotor

8 400 520.83 62 1.92 Rotor

9 400 520.83 62 1.92 Rotor

The six PCM streams bring data from multiple sources in the field to a central location where they are

collected, verified to ensure accuracy, and recorded to provide for subsequent laboratory-based processing

and analysis. The system layout is shown in Figure 5-1 and is described in detail in Butterfield and

Nelson (1990) and Butterfield, Jenks, Simms, and Musial (1990). All measurement transducers provide

linear output volumes that are conditioned as specified in Appendix A and then input directly to PCM

. encoders. The signal conditioning/PCM encoding for streams 1, 2, and 3 each use a Fairchild-Weston

16-channel EMR 600 PCM Data Acquisition System that operates at various bit rates depending on data

bandwidth requirements. The EMR 600 systems have a specified accuracy of 0.2% offull scale over the

operating temperature range -50° to 120 OF. For PCM 1, the EMR. 600 system is located in the datashed

at site 1.1. Its PCM stream is telemetered to site 3.3 over an RF link. The EMR. 600 systems for PCM

streams 2 and 3 are located in the data shed at site 3.3. Analog signals for these two systems are

conducted over cables from local transducers on the VPA and from the tower and nacelle. All the

EMR 600 systems are in locations that offer a conditioned environment to minimize temperature-induced

drift effects. .

Streams 4, 8, and 9 each use a customized signal conditioning system coupled with three Lora! 610

62-channel PCM encoders. The Lora! 610s are specified as having full-scale accuracy of 0.4% over the

operating temperature range of -400 to 185 OF. - This is for digitizing and PCM encoding only. Signal

conditioning accuracy varies depending on measurement type, as described below. These systems are all

located on the wind turbine in the hub-mounted rotor package. The three PCM signals from the rotating

frame are conducted through slip rings and run down the tower to the data shed. All operate at

400 Kbitlsec, which provides a datasample rate of520.83 Hz on all 186 channels. The six PCM encoders

provide the capability to measure 234 channels. Of these, 185 are currently considered active and

necessary for the Unsteady Aero Experiment Deactivated channels are for spare or redundant

measurements, or they were used in previous phases of experimentation. In addition to the 185 direct

measurements, there are five channels allocated for time and 45 subsequently derived ancillary parameters

(i.e., integrated pressure distributions, disk-averaged wind speed, induced aerodynamic forces, etc.).

PCM encoders convert conditioned analog input voltages into digital counts. Overall accuracy is limited

by the number of bits used in the digital code. All channels are sampled with 12-bit resolution that

produces count values in the range from 0 to 4,095. This limits quantizing errors to .024% of full scale,

provides a peak signal-to-noise ratio (SIN) of 83 dB, and defines maximum possible dataaccuracy. All

channels in the Combined Experiment have been set up so that the required data range occupies as much

ofthe available quantizing range as possible. Resulting quantizing errors are insignificant when compared

to other sources of error in the dataacquisition and processing procedures. .

25
TP-4655

6.2 NREL PC-Based PCM Data Reduction System Hardware

In a single PC, the PCM decoding system provides continuous data acquisition to memory or disk from

up to four streams simultaneously. A variety of software packages can subsequently be used to read and

process the data. Single-stream real-time datamonitoring is accomplished from a graphic bar chart display

program.

The full complement of boards in a PC permits data handling from a maximum of 16 PCM streams

containing up to 62 channels each. The boards are Inter-Range Instrumentation Group (IRIG) compatible

and are designed for use with standard PCM encoders. The data streams can be accessed by cyclic

sampling or simultaneous' acquisition or both. Maximum acquisition rates and data storage capacity

depend on PC hardware.

Optional analog interface modules can be used in conjunction with the PC-PCM decoder boards. These

provide digital-to-analog conversion of up to 8 user-selectable channels per PCM stream, or 32 channels

total. Incorporating the PC-PCM system into small portable computers simplifies remote test monitoring

of PCM data. The complete system provides test engineers with the ability to decode PCM data and

perform quick-look data analysis in the field.

6.2.1 Objectives of PC-PCM System Development

The NREL PC-PCM system consists ofAT-compatible hardware boards for decoding and combining PCM

data streams and DOS software for control and management of data acquisition. Up to four boards can

be installed in a single PC, providing the capability to combine datafrom four PCM streams direct to disk

or memory.

Our main objective was to provide a cost-effective PCM decoding system that could be duplicated at our

many test sites to maintain consistency among systems. Future plans include development of an

inexpensive turn-key dataacquisition system that could be used by the wind industry. For many reasons

described below, we decided that a PC-based system was most practical.

We contracted with a local electronics development company (Apex Systems, 1988) to develop the

PC-based PCM decoding capability. We wanted a system built on printed circuit boards that could be

installed in the expansion slots of a PCIAT or compatible computer. The system should include basic

control software to initialize and operate the boards. It should also provide a simple user interface to

allow easy acquisition and examination of datafrom different PCM streams.

We specified four PCM input channels for each board, from which one could be software selected to read

data. A maximum offour boards could be installed, which would allow access to 16 PCM streams from

a single computer. Multiple boards would permit acquisition from up to four streams simultaneously, and

would tag and interleave multiple incoming datainto a contiguous digital time series.

We also specified that databe written directly to PC memory or disk meso This would enable subsequent

data processing and analysis to take advantage of the huge resource of software packages available for

PCs, according to user preference. It also would enable easy development of custom packages in the

many available software languages. The widespread use of PCs also would permit easy distribution of

a developed data acquisition and processing package to interested users.

26
TP-4655

6.2.2 PC-PCM Decoding System Hardware

The PC-PCMhardware boards support a subset of the IRIG PCM standard, designed to synchronize and

decommutate NRZ or Bi-Phase L PCM streams in the range of 1 to 800 Kbits/sec at 8 to 12 bits/word

and 2 to 64 words/frame. Multiple PCM streams (at various rates) can be combined and interleaved into

a contiguous digitaltime series. Maximum datathroughput depends on characteristics of the PChardware,

such as central processing unit (CPU) rate and disk accessspeed. We typically do not super-multiplex

orsubcommutate channels in the .PCM"frames. All channels on a givenPCM encoderare sampled at the

same rate as that required for the highest rate channel. Those channels that do not require the fast rate

are anti-alias filteredto a lowerbandwidth and can subsequently be decimated in software. The PC-PCM

decoder board specifications are summarized in Table 6-2.

Table 6-2. Specifications for PC-PCM Decoder Board

Bit rate

Input streams

Input polarity

Input resistance

Codes

Bit sync type

Input data format

Words per frame

Sync words per frame

1-800 Kbits/sec

4 (only one processed at a time)

Negative or positive

> 10 Kohms

Bi-phase L, NRZ

Phase-locked loop (PLL)

8-12 bits/word, most significant bit

(MSB) first

2-64 Oncludingsync)

1-3 (maximum 32 bits)

In conjunction with the PCM decoderboards, we developed an analog interfacemodulethat reconstructs

analog output from up to eight channels per stream. The basic intent was to provide the ability to use

real-time analog test instruments such as a spectrum analyzer or a chartrecorder. The analog module is

an optional part of the system. Specifications are shown in Table 6-3.

Table 6-3. Specifications for Analog Interface Module

Analog output

Output polarity

Output range

PCM input

Status lights

8 channels (user selectable via thumb wheels)

Unipolar or bipolar

oto 10 V, 0 to 20 V, -5 to +5 V, -10 to +10 V

4 (only one processed at a time)

PLL lock, frame sync, first-in, first-out

(FIFO), disabled

6.2.3 PC-PCM Decoding System Software

The PC-PCMhardware boards are controlled by DOS software writtenin C. Three programs and three

ASCIIconfiguration files providebasic capabilities. The first program, PCMTEST, initializes boardsand

captures data. The second program, PCMDUMP, reads capturedbinary data files. The third program,

PCMBAR, generates a real-time bar chart graphics display. These programs input PCM system

descriptions from DOS ASCn format data files that are easily accessed and modified by the user. A

configuration file (.CFG) contains information describing how PCM hardware boards are configured in

the PC. A stream file (.STM) defines characteristics of each PCM stream. The capture file (.CAP)

27
TP-4655

contains a list of instructions for a capture operation. These parameters and the range of options are

summarized in Table 6-4.

Table 6-4. User-Definable Options for the PC-PCM System

Configuration File:

Base I/O address

Number of cards

Signals per card

Direct memory access (DMA)

channel

Interrupt channel

Buffer size

Buffers

Stream File:

Bit rate

Data format

Signal polarity

Bits per word

Words per frame

Synchronization

Capture Rle:

Card n

Signal =stream

Use

Capture channels

Max frame count

I/O address of the first PCM board (Board 0) (2-3 hex digits)

Number of PCM cards installed in the PC (1-4)

Number of input streams attached to card (4)

DMA channel that PCM board 0 is configured for (5-7)

Interrupt channel that PCM board 0 is configured for (0-15)

Size of memory buffers in bytes (512-65, 024)

Number of memory buffers (2-64)

Rate of transmission in bits/second (1000-800,000)

PCM format (NRZ or Bi-phase L)

Whether signal is inverted (positive or negative)

Bits in each word (2-13)

Length ctframe, including sync words (2-64)

. Binary of hex sync pattem

Specifications for board n (0-3)

Links PCM stream to input signal (0-3)

Which signal to read data from (0-3)

List of channels to capture (1-62)

Total number of frames to capture (optional)

The PCMTEST program can capture any amount of data up to the available space limit. If data are

captured to disk, the maximum amount is determined by the space remaining on the hard disk drive. If

dataare captured to memory, the maximum amount is determined by available remaining system memory.

Larger memory captures are possible by usingextended memory configured as a random-access memory

(RAM) disk. The amount of datato capture is specified in time (seconds), file size (kilobytes), or frame

count

PCMDUMP is a postprocess program used to generate time series data files from the raw binarycapture

files. Thisfacilitates examining PCMdata andinterfacing withdataanalysis software. ThePCMDUMP

program can generate either ASCn or binary data files and can separate an individual stream from a

multiple-stream dataset .

The resulting delivered system had one benefitthat we did not anticipate. Invoked from a batchfile, the

software can reinitialize a board fast enough to enable quick sampling from each input PCM stream.

Therefore, a singleboard can cycle through, sample, and store data from fourstreams rapidly enoughto

update a real-time display run from other application software. Many factors affect the scan rate,

including number of channels, number of samples per channel, and interim calculation requirements.

Typical update rates for a 15-channel display from four PCM streams (including first-order engineering

unit conversion and derived parameter calculations) occurin less than a second The usefulness ofPCM

stream scanning depends on the nature of the data because intermittent sampling may cause aliasing, or

28
TP-4655

transients may be missed. However, for many of our averageddataapplications, the monitoring of many

.channels by scanning across multiple streams is very useful.

6.2.4 Data Flow in the Computer

A clear understanding of the data-flow inside the computeris helpful in understanding the capabilities and

limitations of the PCM decoder board. Figure 6-3 shows the dataflow inside the PC, described below.

PCM data streams can be input directly to the PC-PCM decoder board or interfaced through an analog

module. The analogmodule allows the user to selectup to eight desiredchannels(via thumb-wheel dials)

for analog output The analog voltage output can be selected in the 10- or 20-V span range, bipolar or

unipolar. The analogmodule alsointerfacesthe PC-PCMboardsto panel-mounted liquid-emitting diodes

(LEDs)to inform the user of system status. (TIle status LED panel could also be built independently of

the D/A system.) Status lights indicate capture activity, PLL status,frame sync status, PC memorystatus,

and error state.

The PCM decoder boards are under the control of the capture software running in PC system memory.

This program can be ron on its own or via user application software. The capture program writes

binary-format tagged PCM data. Each dataword is tagged with its correspondingPCM board number.

Captured data can be accessed by the applicationprogram through memory or disk files.

The capture softwarereads user-definedparametersfrom the capture control disk files, then initiates and

terminates the capture operation. Before initiating capture, the direct memory access (DMA) controller

is initialized to define the starting address and size of the first memory buffer. The DMA controllerhas

a special address generator that allows it to move data from the PCM decoder card to the addresses -in

memory. When capture is initiated, the DMA controller moves data from the PCM board to the rust

memory buffer in 16-bit words. When the buffer is full, the DMA controller informs the PCM decoder

card, which in turn generates an interrupt to the capture software.

Upon receiving the interrupt, the capture softwarereinitializes the DMA controllerto transfer datato the

next availablebuffer. This process is repeateduntil the capture is complete. While the buffers are being

filled, application software could simultaneously access the data in the full buffers. Flags are provided

for each buffer to define when they are full, empty, or in use.

This structurehas many advantages. First, the DMA controllermovesdatafrom the PCM decoderboard

to memory more quickly than a software transfer does, and it is an independent process. The DMA

controller actually takes over the PC!AT bus when data are transferred and does not burden the

microprocessor, This makesthe application softwaresimplerand moreefficient Memorybuffersprovide

anotheradvantage. When dataare beingtransferredto the hard disk, these buffersstore datauntil the hard

disk can rotate to the proper sector to write the data. Without these buffers, data would be lost

6.2.5 Data Capture Performance Estimates

In single-stream mode, a typical PC/AT can capture PCM data to disk at rates up to 800 Kbitslsec. For

multiple-stream disk capture, quantifying performance is difficult due to many possible combinations of

PCM stream rates and PC capabilities. An algorithm for estimating disk data capture rate is

nCR = 16 III (BR / BPW)*(CWPFIWPF)

29

(6-1)

TP-4655

where:

DCR = PC data disk capture rate in bits/second

BR = Incoming PCM bit rate in bits/second

BPW = Data bits per PCM word

CWPF = Words captured per PCM frame

WPF = Total words Per PCM frame, including sync.

The data capture rate (DCR) for multiple cards is the sum of the DCRs for each individual card.

To provide some rough performance estimates, a test was run using four PC-PCM boardsinstalled in a

25-MHz 80386-based PC. A PCM simulator was used to generate 62 channels of 12-bit words in

Bi-Phase L format with2 syncwords perframe. Datawere captured to contiguous blocksof disk storage

space. The PC system could continuously capture to disk all channels of data from two 800-Kbitlsec

streams. It could alsocapture all channels from four400-Kbitlsec streams. The maximum occurred with

three 800-Kbitlsec streams, each capturing 45 channels. At rates abovethis, the hard disk couldnot keep

up with incoming data, and capture was terminated by a buffer overflow error condition.

Based on Eq. 6-1, the corresponding upper limit of disk data capture for this configuration is

approximately 2.25 Mbitslsec. The PC's hard disk wasrated at 10Molts/sec, indicating that the required

PC disk speed should be 4 to 5 times the maximum data capture rate in order to ensure adequate

performance. Manyfactors are likely to affectthese values, including disk fragmentation, disk interface

type, disk interleave, buffer size, CPU speed, and otherinstalled PC options.

With the same systemconfiguration, there were no performance limits when capturing datato memory.

PCMdata fromfour 64-channel, 800-Kbitlsec streams were successfully captured to an extended memory

RAM disk. This is useful for providing higher-rate capture, but data quantities are limited because of

memory restrictions. Large amounts of memory are less common and more expensive than comparable

disk space.

6.2.6 Architecture of PCM Decoder Board

The PCMdecoder boardhas a programmable bit detector for extracting the ones and zerosfromthe PCM

signal. These are passedon to the frame and wordprocessing sectionwhere the words are extracted and

then interfaced to the PC. The following paragraphs discuss each of these in detail.

Bit Detector: Figure 6-4 shows the bit detection circuitry. A multiplexer controlled by the software

selects betweenanyone of fourinputsignals. Following the multiplexer arebuffer, :filter, andcomparator.

These circuits convert the selected signal to digital levels. The data clock synchronizer extracts the bit

clock rate from the incoming signal. The data bit detector circuituses the bit clock and the signal from

the comparator to generate a data bit stream of ones and zeros.

Frame andWord Processing: Figure6-5 shows the decoder boardframe synchronization circuitry. The

bit clockclocks the data bits into both the frame synchronizer andthe serial-to-parallel circuit. Theframe

synchronizer is programmed with the sync words. Thisinformation is used to detectand synchronize on

31
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the data frame. The serial-to-parallel circuit is nothing more than a shift register with parallel output.

When commanded by the frame synchronizer. the serial-to-parallel circuit strobes a complete word of

information into the FIFO buffer. A FIFO buffer is necessary because the PCM stream is continuous with

no gaps in the data, whereas the pC!AT bus cannot continuously accept data. The FIFO acts as a

variable-sized buffer, holding the data until the PC/AT can pick it up. When a large amount of data is

captured to the hard disk and the incoming bit rate is very high, itis possible for the FIFO to fill up faster

than it can empty. When this happens. a FIFO full error is generated, a warning signal level is activated.

and data capture stops. A frame termination counter option allows the user to specify the number of

frames before the capture process is automatically terminated.

B~t Clock

Signal 0-

Signal 1- 4 to 1 Buffer Filter

signal 2- Mux

signal 3-

0 -

I

I

Comparator I Clock Data bit

sync detector

Datal Bits

-I

.

Figure 6-4. Decoder board bit detector

o out

s Serial - to

- parallel

Frame I

sync FIFO

buffer

L FIF

Frame

termination

counter

Data bit

Bit clock

Figure 6-5. Decoder board frame synchronizer

32
TP-4655

PCInterface andControl: Figure 6-6 shows PC interface and control circuits that interface the PCM data

decoder to the PCIAT bus. The FIFO output must be connected to the PCIAT data bus to transfer data.

This process is controlled by the control block, which also controls programmable functions and interfaces

to the multiple-board arbitration circuit The multiple-board connector provides an independent data path

between boards. The master board determines which boards have dataready to transfer to the PCIAT bus.

If more than one board has data at the same timet the arbitration circuitry controls the order of data

transfer.

FIFO Out.---.----I

16 bits

PC bus

interface

Control

Address bus

Data bus

ontrol bus

MUltiple board

connector

MUltiple board

arbitration

Figure 6-6. PC interface and control

6.3 NREL PC-PCM Data Reduction System IIQuick-Look" Software

The Quick-Look program is a comprehensive software package designed to manage data from multiple

incoming data sources. It provides a way to quickly examine field data in an experiment test environment.

Program menus allow easy access to options that facilitate organization, acquisition, processing, and

display of information from many PCM data streams.

The program presumes that a PC cannot process all incoming data in real time. It compensates for this

by using techniques to reduce the quantity of incoming data to a manageable level. The data reduction

techniques impose limitations that the user must be aware oft and they may not be appropriate in certain

situations. However, for most of our quick-look requirements, the imposed limitations are not of concern.

In our typical field experiments, we have found the Quick-Look program to be extremely beneficial,

especially for monitoring in real time and conducting multichannel calibrations. The ability to grab

contiguous time series data blocks from multiple streams allows access to high-rate phenomena Graphic

review features provide the test engineer with a means to quickly interpret results. Data bases providing

histories of channel configurations and calibration coefficients are essential for accurate postprocessing

of recorded raw data sets.

6.3.1 Overview of the Quick-Look Program

The Quick-Look program is used on a DOS-based PC interfaced with peripheral PCM decoders in an

experiment test environment. The major objective in developing the program was to provide a way to

quickly examine data from PCM streams in the field. Other objectives include on-line channel data base

management, hardware debugging capability, and automated calibration procedures.

33
TP-4655 '

Menus are presentedto the user enabling quick selectionof desired options. Each menu containsa title,

followed by lines listing current availableoptions. The user uses the arrow keys to move a highlighted

bar up and down to select the desired operation. From there, anotherlevel of menu options may appear,

or option execution may begin.

The main programmenu presentsthe user with options that are summarized in Table 6-5. These options

identify all the basic features of the Quick-Look program.

Table 6-5. Quick-Look Program Features

Hardware Setup The definitionof all parameters relatedto interfacing the PC with

peripheral PCM decodingdevices.

PCM Configuration Data Base Data base in whichto define and maintainthe characteristics of all

potential incoming PCM streams.

Channel Data Base Data base in which to define and maintain information associated

with'all measured data channels.

Derived-Parameter Data Base Data base in which to establish and organize ancillary derived

channel equations.

Data Acquisition The selectionof.channels, monitoring of current conditions,

collecting of data, and storing of it in a disk file.

Recorded Data Display Comprehensive graphic or alphanumeric display of previously

recorded data sets.

Channel Calibration Multiple-channel data processor using least-squares linear

regression to generate calibration coefficient.

File Maintenance Systemto organizeand catalog experiment-associated data files

and channel data bases.

Test Event Log Record of the sequenceof experiment events.

Typical components of PC-based data acquisition systems commonto both the Quick-Look system and

most commercial data acquisition systems are not described here. This report concentrates on the

particularcapabilities of the Quick-Look program related to quick handlingof PCM data in the field and

conducting of calibrations. Although this program was developed to allow the PC to be interfaced with

PCM data, the capabilities for data management outlined here could be applied to other types of

telemetry-based experiment data handling systems as well.

6.3.2 Limitations of PC-Based Data Processing

A basic premise of the Quick-Look programis that the PC cannot process all incomingdata in real time.

Becauseof DOS and CPUlimitations, data collectionand data processing are not done at the same time.

These tasks could be combined if incoming data rates are sufficiently slow. However, for most of our

applications. we have found that the typical PC cannot concurrently do both adequately. Ifthe processes

are independent, the CPU can be fully dedicatedto each task separately. This allowsaccessto higher-rate

incoming data and provides greater data processing capability.

To compensate for the limitations imposed by the pc. two techniques can be used to effectively reduce

the quantity of incoming data to a manageable level. First, the PCM data streams can be periodically

sampledat a controllable rate. This allowsthe PC's CPU to selectively alternate betweendata acquisition

and processing. Second.data can be recordedto disk or memoryover a given durationof time'andthen

postprocessed.

34
TP-4655

These data reduction techniques impose restrictions that the user must be aware of, and they may not be

appropriate in certain situations. For example,transients may be missed,or aliasing could be introduced.

To provide data valuesrepresentative of existing conditions, the data segments should be stationarytime

history records (Bendat and Piersol, 1980). The Quick-Look program provides many features that allow

evaluation of time series data. It is up to the user to ensure that the data segments are sufficientlylong

and statistically meaningful to produce adequate results.

For most of our quick-lookrequirements, the limits imposed by the PC-based system are not of concern.

In our typical field experiments, we have found this system to be extremely useful, especially·for

monitoring current conditions and conducting channel calibrations. We do not, however,use this system

as a substitutefor full data processing. Usually, all PCM datastreams are recorded independently of this

system to provide complete data sets for comprehensive postprocessing, as shown in Figure 6-2.

6.3.3 Interfacing a PC to ·the PCM Data Streams

The main function of the Quick-Look program is to interface a PC with PCM data. This requires some

type of PCM decoding hardwarewith the ability to transfer data into a PC. The data transfer can be done

in a variety of ways, such as through a simple but slow serial communication port or complex but fast

DMA buffers. The PCM decoding hardware can be outside or inside the PC. This report assumes that

PCM dataare providedto the Quick-Look programthrough a PC-basedPCM-decoding hardware system

developedby NREL (Simms and Butterfield, 1990). The Quick-Look program could support other PCM

decoders if appropriate interfacedrivers were provided;however,some of the softwarefeatures described

here depend on unique capabilities provided by the NREL decoding system.

The NREL PC-PCM decoding system consists of printed circuit boards (APEX Systems, 1988) that fit

directly inside the chassis of a PCIAT or compatible computer and basic control software. PCM dataare

decoded on the board and DMA transferred to PC memory or disk. One board can decode one PCM

stream at a time. Up to four boards can tie installed into a PC, permitting data from four streams to be

simultaneously combined. The Quick-Look programbuilds all data files necessary for settingup PC-PCM

boards and overlays control software to accomplish data acquisition.

The full complementof four boards in a PC allows the Quick-Look program to manage datafrom up to

16 PCM streams. Each board has four inputs and can be quickly reconfigured to cycle through the input

to sampledatafrom differentPCM streams. Variouscombinations of cyclic or concurrentacquisitioncan

be used. Maximumdata collectionrates vary, depending on hardware limitationsand other variablesthat

are discussed below. The boards support standard-format IRIG-compatible PCM streams with bit rates

in the range of 1000 to 800,000 bits/sec and a maximum of 64 data words (including sync) per frame.

Based on 12-bit data resolution, channel sample rates from 1.3 to 33,000 Hz are possible.

The Quick-Look program assumes that each channel of input datais a time history record and that each

record has a constant sample rate. However, because data can originate from multiple PCM streams of

varying rates, channels may have different sample rates. Data are transmitted to the program through

arrays eitherin memory or on disk files. H multiplePC-PCMboards are used, datafrom up to four PCM

streams can be collected simultaneously. All incomingdataare meshedinto a single file. After they are

collected, they are decoded for display by the Quick-Look program. H a single PC-PCM board is used,

it is still possibleto cyclethroughand monitorup to four PCM streams,but simultaneous acquisition from

multiple streams is not possible. Software decoding of subcommutated or super-multiplexed PCM data

is not supported.

35
TP-4655

To keep track of up to 16 PCM input, the Quick-Look program provides a locationmatrixinto whichthe

user assigns incoming PCM streams to theirrespective input locations. When data are requested from a

particular PCM stream, the program uses the matrix to determine how to set up acquisition so that the

correctpcM streams are accessed.

During acquisition of PCM data, all values are based on raw counts, which are derived.from binary data

words that have been decodedfrom the PCM datastreams. Data resolution is determined by the number

of bits used to represent each measured data value. We typically use 12-bitresolution, which is 1 part

in 212, corresponding to count valuesranging from 0 to 4,095.

The Quick-Look program interprets the raw count values provided by the PCM decoding hardware and

converts them to engineering units. As described above, because of the potentially large amount of

incoming dataand the limitations of the PC, the Quick-Look program does not acquire and process the

data simultaneously. It uses techniques of contiguous or sampled acquisition to reduce the volume of

incoming data to a manageable level. These techniques are described below.

6.3.4 Contiguous Data Acquisition

In contiguous data acquisition, data streamsare recorded as time historyrecordblockswith no gaps. Data

from up to four streams can be acquired simultaneously to a disk file up to the limit of available disk

space. The datablocks are then postprocessed using features of the Quick-Look program or other data

analysis programs. .

While contiguous data collection is occurring, no other process can run. After the block of data is

acquired, summary statistics are presented on the monitor display. From these, the user can decide

whetherthe data set meets the necessary criteria.

The required number of samples is specifiedby the user as a time duration. The total resulting number

of data points depends on bit rate, numberof streams, and channels per stream. Large quantities of data

are not practical in this mode. Upward from 50,000 individual datavaluesstart to become difficult for

two reasons:

1. Disk storage resources are quickly exhausted. Raw data are input to the program in an efficient

binary integer format However, to produce practical data sets, they are converted to engineering units

and copied to an ASCII file in 80-column E12.3 format with corresponding time. This is very readable

(and printable) but not storage efficient

2. It takes a longtimetoprocess. It is CPUintensive to decode and sort the raw binarydata. especially

for multi-board acquisition. Data from the PCM streams are intermeshed in one binary file as they are

acquired. Each data valueis encodedwith a tag that identifies the streamand channel it came from. The

tag has to be removed from the data and used for sorting. The raw data valuesusuallyrequireconversion

to engineering units. Slower-rate data are interpolated to the rate of the fasteststream. The final data file

is chronologically organized as a time series,with eachrecordconsisting of a time value followed by data

values from each requested channel for that time.

6.3.5 Real·Time Data Monitoring

Sampleddata acquisition is used to provide a real-time data monitoring capability. The incoming PCM

streams are periodically sampled to acquiresmallsegments of contiguous data The segments are quickly

processed and displayed to show current conditions. The process is continuously repeated. Up to 135

channels from any combination of incoming PCM streams can be displayed. Each representative value

36
TP-4655

for each channel is determined by averaging 1 to 10,000 contiguous samples. The user selects channels

for display and defines an appropriate averaging interval.

Data monitoring is a cyclic repetitive process that is controlled by the Quick-Look program. This is

shown in Figure 6-7 and can be described in three basic steps:

1. PCM-stream data acquisition is initiated to obtain datasegments from each requested channel. The

. Quick-Look program overlays an independent data capture program that initializes the PCM decoding

boards, locks onto the PCM streams, and initiates datacapture. All PCM streams containing requested

channels are sampled to obtain enough contiguous data frames for the required averaging interval. Data

are written to RAM disk, and control is returned to the Quick-Look program.

2. The Quick-Look program reads data from RAM disk and sorts by requested channel. Mean and

standard deviations are calculated for each channel from thetotal number of samples in the sample period.

PCM data in units of counts can be converted to engineering units using the slope and offset from the

channel data base. If derived channels are requested, calculations are performed using equations from

the derived-channel data base. Any combination of derive channels and measured channels can be

displayed.

3. Resulting values are displayed on the screen in either raw PCM counts or engineering units. The main

reason for displaying counts is to conduct calibrations. The screen display is an alphanumeric

representation of the current conditions for the requested set of data channels. The program monitors in

pages of 15 channels each. Only one page is displayed at a time. The user can easily select from among

several pages by keying the desired page number. All pages are updated simultaneously after each set

of data is processed. Each channel is displayed beginning with channel number, name, and units from

the channel data base, followed by the current mean and standard deviation.

For example, selected channels would be displayed on the monitor in the following format:

201:Anemometer #1 (mls) .........................••... 1.067E+Ol (2.502E-Ol)

307:Power Supply (Volts) 2.502E+OO (6.745E-02)

402:Bending Moment (N-m) . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5.678E+02 (3.456E+Ol)

The first digit of the channel number identifies the PCM stream, andthe next two digits identify the data

word The mean and standard deviation values continuously change as data monitoring cycles. The

monitor display may lag behind real time by a few seconds, depending on calculation overhead. For the

Combined Experiment datastreams of Table 6-1, practical data monitor update rates of 1 to 10 sec were

easily achievable.

At any time during data monitoring, data collection can be initiated via a user-entered keystroke. This

causes monitor-displayed mean and standard deviation values to be permanently recorded in an ASCn disk

file, The data monitor will continue to update and will note that data collection is in progress. The

collection can be suspended and restarted at any time. Upon termination of data monitoring, collection

is stopped, and mean values for the entire period are calculated. These are inserted at the beginning of

the data file, and the file is closed and saved. The user is notified ofthe file name, is shown the file for

browsing, and has the option of printing a copy.

37

TP4655

6.3.6 Data Monitoring Features

Typically, the monitor displays current rapidly changing conditions. The current values are calculated by

averaging contiguous samples. Another level of averaging is also possible. A parallel monitor display

is available to show long-term averaged values that are determined from the current condition values.

Keystrokes are used to toggle between the long- and short-term displays. For long-term averaging, current

display values are summed for each channel (measured and derived) over the averaging period. At the

end ofeachperiod the sums are divided bythe number ofscans, and the average display is updated. The

user defines an appropriate long-term averaging period (typically in minutes).

Because up to 135 data channels can be monitored, it would beimpractical to expect the user to re-enter

the list of desired channels each time he or she wants to monitor data. To overcome this, the program

provides a means of defining and saving collections of display channels. A user-defmed name is

associated with each collection. The user assembles a collection of channels, and the Quick-Look program

adds it to a list of available selections. When data acquisition is initiated from the main menu, the user

is presented with a menu containing the list of all available collections of channels and selects the

appropriate one using the arrow keys. It is also possible to modify an existing collection, delete obsolete

ones, and define new ones.

For real-time datamonitoring, a range-check feature exists that highlights the display when a value is out

of range. The user enters the maximum and minimum allowable values for a particular channel in the

channel database. If a value is outside the range, it is displayed with a conspicuous red background.

Another type of real-time data monitor is provided in the form of a graphic bar chart display. This can

be invoked at any time during alphanumeric data monitoring via a user-entered keystroke. Up to 62

measured channel values are graphically displayed.as bar graphs on the screen. The Quick-Look program

sets up the bar chart display with the desired PCM stream configuration and channels. The bar chart

monitor shows datain units of counts and can be used on only one PCM stream at a time. Its display

update rate is very fast, typically many times per second. It is useful for quickly checking a large number

of channels at once because dead channels are readily detected and easily identified.

6.3.7 Factors Affecting Data Monitor Rates

The rate at which the datamonitor display updates itself is affected by many factors. Some depend on

which program options the user selects. Others are inherent in the hardware. Some of the factors are

1. CPU speed of the PC

2. Number of channels to display

3. Number of scans to average for each sample

4. Whether engineering unit conversion is done

5. Whether derived parameters are calculated

6. Overhead of the PC-PCM board capture software

7. Bit rate of the incoming PCM stream(s)

8. PCM stream consistency and quality

9. Whether data are captured to RAM or hard disk

10. Whether simultaneous or cyclic acquisition is used

11. Whether data collection is occurring.

39
TP-4655

6.3.8 Data Base of PCM Stream Configuration

TheQuick-Look program provides a form intowhich a setof configuration parameters defining eachPCM

stream can be input The parameters are then usedto set up decoding hardware to access streams whose

channels are requested. The configuration parameters are

1. PCM stream title

2. Number of data words per frame (data channels)

3. Number of sync words per frame

4. Binary sync bit pattern

5. Bit rate in bits/second

6. PCMdata format (Bi-phase L or NRZ)

7. Signal polarity

8. Bits/word

9. Samples to average.

6.3.9 Data Base of Channel Parameters

A data base is kept for each channel of each PCM stream. A maximum of 70 channels per stream is

allowed. The data base consists of a set of user-definable parameters and corresponding data. For the

Combined Experiment. the following parameters fields are used:

1. Channel description

2. Sensor location

3. Sensor type

4. Sensor ID number

5. Anti-alias filtersetting

6. Sample rate

7. Engineering data units

8. Slope (engineering units/count)

9. Offset (engineering units)

to. Range maximum

11. Range minimum

12. Reference channel for calibration

13. Low, zero (mid), and high calibration values

14. Flag to print mean values to a log file

15. Date and time of latestrevision.

Parameters 2 to 6 areavailable for bookkeeping purposes, andotherthanfor comprehensive printouts, they

are not used elsewhere in the program. Values do not have to be entered in these fields, Parameters 1

and7 to 14areusedin various otherplaces in the software. Values mayneedto be entered in thesefields

depending on the program option selected.

The channel data base option of the Quick-Look program provides access to these parameters for any

channel on any PCM stream. The user is presented with a form on the screen that displays current

parameter values, which can easily be updated or modified. If any changes are made, a new version of

the data base file is written and becomes the current version. Parameter 15 is updated automatically if

any changes are made in any field. •

40
TP-4655

Previous versions of the channel data base are retained so that a history of the channel, including

calibration coefficients, is available. The program allows previous versions to easily be recovered. nus

is especially useful for postprocessing raw PCM data recorded on tape, allowing ready access to data

values in correct engineering units.

6.3.10 Derived Channel Data Base

A data·base of all derived channels is .maintained by the Quick-Look program. A derived channel can

be a function of many channels from multiple PCM streams. When the user selects the derived-channel

data base option, a simple form is presented in which the channel description and derived equation are

entered. The equation may contain constants, functions, or measured channel numbers. Upon completion,

the derived-channel information is saved and made available for use either in monitoring or generating

data files.

6.3.11 Rapid Multi-Channel Calibration Capability

Only linear engineering unit conversions are provided, one slope and offset pair for each channel. The

slopes and offsets can be input manually into the channel data base, ifknown. They can also be generated

based on measured data obtained during "calibration runs" and automatically inserted into the channel data

base. It is possible to quickly generate and update calibration coefficients for many channels from many

PCM streams simultaneously. There are four options for calibration runs:

1. 3-level highlmidllow calibration data

2. 2-level highllow calibration data

3. I-level zero calibrations (determines offset only)

4. A function of another "reference" datachannel.

For the first two options, PCM count data are collected at the constant calibration levels for a short

duration of time and stored in a file. The channel data base contains a value in engineering units that

should coincide with the measured count value at each level. The count data are read from a file and

compared to the reference values. A least-squares regression line is generated from which a slope and

offset are found, and correlation statistics are calculated.

For the third option, count values corresponding to the channel zero (or any known level) are stored to

a file. The data base zero value is used as a reference, and a new offset is calculated.

.For the fourth option, engineering unit data are concurrently measured from a reference channel used to

generate coefficients for the channels to be calibrated. The relation between the reference channel and

the channel to be calibrated is limited to a simple user-defined mathematical function entered in the

channel data base. A least-squares regression line is generated to obtain the relation between the two

variables. This allows a ramp calibration to be done, in which the data values are distributed over a wide

range as opposed to discrete known levels.

Upon completion of a calibration run, the user is presented with a page of summary regression statistics,

other information pertinent to the least-squares fit, and new calibration values. The user can opt to accept

or decline the cal coefficients based on these statistics. He or she can also set up criteria that automate

the acceptance process using defined tolerances. For example, the user can identify acceptable ranges of

standard error and correlation coefficients. If the regression statistics are within the ranges, :cal

coefficients are automatically accepted and inserted in the data base. This Provides a means of quickly

41
TP4655

calibrating many channels. It has proven very useful in the Combined Experiment, in which calibrations

of 128 pressure channels are required every 5 min of testing.

6.3.12 Event Log File

The Quick-Look program provides a means for maintaining a log of events that occur during an

experiment The user can set up a log file at any time. The log feature automatically notes when data

acquisition occurred and summarizes channels used and mean data values during the interval. If any

changes are made in the channel database, it is noted in the log that a new version was generated. If any

channels are recalibrated, their new calibration coefficients and regression statistics are included in the log.

The user can easily enter comments, which will be time stamped.

6.3.13 Quick Review of Recorded Data

Upon completion of data collection to a file, the file is immediately available for review. It is presented

to the user and can be scanned and printed. Channel values can also be displayed easily using included

graphics programs. Two- (2D) or three-dimensional (3D) plot capability is available. Basically, all the

user has to do is select a datafile, plot type, and desired channels. Available plot types are as follows:

• 2D time series plots: Channel data are plotted on the ordinate axis with time on the abscissa. Axes'

maximum and minimum are automatically chosen based on datarange. Channel dataare plotted in

appropriate units. A legend that uses the channel name to identify each curve is automatically

included. Up to 10 channels of data can be displayed on one graph.

• 2D X-vs.-Yplots: Channel dataare plotted on both axes for comparison. A legend is generated from

the name of each Y-axis channel to distinguish among multiple comparisons. Up to 10 comparisons

can be displayed on one graph.

• Custom 2D plots: This option provides the user with some flexibility to generate custom-format plots.

• 3D plotsoftime-vs.-channel-vs.-tJata value: This option provides a quick way to look at time series

from many similar channels simultaneously. Time is plotted incrementally on the X axis. (It is

assumed that the scans occur at even intervals of time.) Selected channels are plotted on the Y axis

incrementally in the order in which they were selected. The datavalue magnitudes are plotted on the

Z axis. The XYZ values are shown as a surface in three dimensions. Any deviation among channels

is readily noticeable on the plot surface. Appropriate surface display depends on the particular data

set, and display options are available to improve the view.

6.4 Combined Experiment Data Processing

Data processing requirements depend on what the dataare to be used for. Data from the Combined and

Unsteady Aero Experiments are destined for a wide variety of different potential uses, and it is difficult

to specify generic requirements. There are certain in-house projects and applications that dictate initial

necessities. Some of the subcontractors have also specified their needs. A channel measurement may

require greater accuracy for some applications than for others. We have attempted to incorporate the

measurement needs from all potential sources and, in addition, anticipate what future dataanalyses might

require. These measurement requirements are summarized in Appendix B.

The main objective is to provide channel data measurements within the defmed tolerance ranges to the

specified levels of confidence. It would be impossible, however, to make all measurements to these levels.

42
TP-4655

With 239 total channels, there is always the potential for some to be out of commission, not working

properly, or not in calibration. It is therefore the test engineer's job to determine the severity of out-oftolerance data channels. This depends entirely on the objectives of the particular test It is the duty of

the test engineer to ascertain what channel measurements are critical for that test. Ifcritical measurements

are within required tolerances, the dataset is considered valid, and those channels that are out oftolerance

are listed and noted so that subsequent data users are aware of their status. For example, if a blade

.azimuth signal is out of tolerance, but the test requires non-rotating data, the azimuth signal accuracy is

not critical to the validity ofthe dataset If, however, critical channel measurements are out of tolerance,

the data set is considered invalid and is not used. It is important for the test engineer to be able to assess

this in the field so that he knows that it is necessary to re-acquire the data set

Most of the tests conducted under the Combined Experiment require that pressure channels be within

specified tolerances to a confidence level of one standard deviation. This pressure measurement accuracy

criteria is typically the determining factor for accepting or declining a data set because these measurements

demand the least allowable error. There are also varying requirements that certain other important data

channels be functioning properly. The test engineer weighs the results of the calibrations of the critical

channels while considering the objectives ofthe particular test to determine ifthe data set is worth further

postprocessing. The test engineer has many tools at his disposal in the field for assessing data quality and

can usually successfully identify valid data sets. Not only can he perform calibrations, but he can also

monitor conditions in real time, cross-check redundant measurements, check acceptability of derived

parameters, and scan channels for out-of-range data. This greatly reduces the amount of invalid data

submitted for subsequent time-consuming postprocessing.

6.4.1 Measurement Accuracy

Under no circumstances do we use the manufacturer-specified accuracy of any transducer, signal

conditioner, or PCM encoder. We also do not rely on manufacturer calibrations or manufacturerrecommended calibration intervals; Le., that transducers or equipment calibrated at recommended intervals

will unconditionally provide accurate results. Rather, accuracy is determined by conducting regular

periodic pre- and post-calibrations on the full data path of all measured channels. The results of the

calibrations are then used to specify measurement accuracy.

Pre- and post-calibration sequences were designedandare utilized to provide a direct measurement of data

accuracy. Pre- and post-calibrations are performed on the complete data path of each channel for each

data set Two criteria have to be met to ensure adequate calibrations. FIrSt,regression statistics resulting

from calculated coefficients of each calibration are required to lie within specified error limits. Second,

if the difference between the pre- and post-calibration coefficients exceeds the specified tolerance, data

collected during the interval between calibrations are considered out of tolerance for that channel.

Measurement tolerances and calibration procedures for all channels are shown in Appendix B.

.Calibrations for all channels are conducted at time intervals sufficient to ensure the accuracy of

intermediate data and were determined from test experience. These time intervals vary from minutes to

months, depending on the transducer or system component being calibrated and the required channel

accuracy. They are categorized according to calibration procedure and are listed in Section 6.4.3.

The objective in calibrating the full datapath is to measure the accuracy of all components of the data

acquisition system that affect data measurement This includes the transducer itself, connecting cables,

signal conditioner, and AID converter. Full data path calibrations are conducted on all channels. For the

Combined Experiment, they are performed in two basic ways:

43
TP-4655

1. Single-part or "end-to-end" calibriltWns: The most preferable way to calibrate a channel is to

directly measure the full-channel response using an external reference that produces a known result That

way, all the components along the data path are calibrated together, and the accuracy of the full system

can be calculated (i.e., blade pulls or reference pressure transducer).

Z. Two-part calibriltWns: For some channels, it is not possible -to calibrate the transducer in situ. For

these, full-channel accuracy is determined from two calibrations, an electronics calibration and a transducer

calibration. The electronics calibration is performed by replacing the transducer input signal with a known

- precision reference voltage. This measures the response of the electronic portion of the signal path

(mainly the signal conditioning and AID conversion systems), which is usually most prone to drift. The

accuracy of the transducer is determined by external pre- and post-calibration to ensure that it remained

within tolerance during use. A good example of this is the wind speed channels, where the electronics

are drift calibrated with each data set, but the anemometers themselves are calibrated seasonally in the

wind tunnel. In these cases, the root-mean-square (RMS) sum of the accuracy values from various

component calibrations determined the overall channel accuracy.

Procedures for performing calibrations to produce measurement accuracy within required statistical

significance levels are detailed in the calibration procedure column of Appendix B. Those channels in

which the transducer requires an external calibration (calibration procedure prefixed by an E) are two-part

calibrations. All other channels are calibrated with an end-to-end calibration. Some channels (such as

pressures and strain gages) require two end-to-end calibrations, one to calculate slope and another to

calculate offset

The pre- and post-calibration strategy assumes that the channel measurement stayed within calibration

during the intervening period. Obviously, this may not be the case, but because it is impossible to

continuously calibrate channels, some assumptions have to be made. We have conducted many calibration

studies to define appropriate calibration intervals necessary to ensure data accuracy. We have also devised

many built-in "sanity checks," which are used to periodically check the data validity ofimportant channels.

6.4.2 Features of the Custom Data Calibration System

It is the objective of the test engineer in the field to produce measurements that are within the tolerance

limits specified in Appendix B. It is very difficult, however, to completely ensure the accuracy of all

channels, considering the limited facilities and time available in the field. To guarantee that all channel

measurements are within the required error tolerance limits is no small task, especially when each 10 min

of operation requires re-calibration of at least 200 channels, some of them to extremely tight tolerance

limits (to calibrate pressure channels to .2% full-scale allowable error requires least-squares linear

regression calculations on hundreds of data points for each channel). For that reason, a custom data

calibration system was developed with the specific objective of assisting the test engineer in the field.

It provides a variety of tools to initially assess the accuracy of the data by performing calibrations and

examining important or critical channel measurements. This strategy has proven to bevery useful because

the test engineer can quickly identify and eliminate out-of-tolerance data. It saves having to spend a lot

of time and effort postprocessing data sets only to find that they contain worthless information. It also

lets the test engineer immediately know the status of the test matrix. Subsequent rigorous postprocessing

analyses are performed to provide final data accuracy values.

The custom data calibration system consists of 3 COmponents:

1. Microprocessor-controlled, rotor-mountedPSC: As seen in Appendix B, pressure measurements are

those that require the most stringent calibration tolerances. The PSC was designed and built to provide

44
TP-4655

in-flight National Institute of Science and Technology-traceable reference calibration pressures to all

pressure ports. While the machine is operating, the test engineer can initiate a command from the ground

that causes the pressure transducers to replace the measured tap pressures with reference calibration

pressure on all 128 ports simultaneously. The reference pressure ramps up and down across the

measurement range to allow acquisition and calibration of each channel to the required level ofstatistical

significance. The PSC also provides necessary anti-alias filtering and high-quality signal conditioning on

all incoming analog pressure measurements to minimize drift and ensure data accuracy.

2. High- and low-calibration shunt system: For some channels, it is impossible or unnecessary to

perform a completeend-to-end calibration in the field. A good example is wind speed. The anemometers

only require annual calibration in the wind tunnel. The electronics, however, from the output of the

transducers through the signal conditioning and data acquisition system, require more frequent calibration

to compensate for drift. This is done by periodically replacing incoming transducer voltages with a known

precision reference voltage. A single-point calibration is used to compensate for electronics drift by

providing a reference for re-calculating the channel offset in engineering units. A two-point calibration

can be used to provide a slope check.

3. PC-based Quick-Look automated calibration system: The experiment test environment rules out the

use of significant resources in the field to verify calibration results. We therefore developed the QuickLook system, which is a PC-based PCM data processing package. It simplifies the process of acquiring

selected sets of channel data during calibration intervals and then automates generating engineering unit

calibration coefficients and maintaining data bases of calibration histories. It also allows easy examination

and channel cross-checking in real time. The Quick-Look system combines custom-developed PCMdecoding hardware boards with a custom-written software analysis package. The hardware boards are

inserted into a PC to convert incoming PCM stream data to disk files. This capability is described in

detail in Simms (1990). The software was developed to provide the test engineer with a quick way to

conduct multi-channel calibrations in the field. It is described in Simms and Butterfield (1990).

It would have been impossible to conduct the frequent calibrations required by the Combined Experiment

and manage all the resulting information without custom data calibration system capabilities. In previous

experiments, we had to rely on laboratory-based postprocessing analyses to provide calibration results.

Often, by that time, it was too late to go back into the field if subtle or overlooked problems surfaced

when analyzing data. At the time of planning for the Combined Experiment, we only had a basic field

system that could display a limited number of channel data values. Cost-effective commercial systems

that could provide more comprehensive field analysis were not available. We therefore had no choice but

to develop our own system to satisfy specific field data verification requirements For that reason, the

Quick-Look system, in conjunction with PC-PCM decoding boards, was developed. Recently, low-cost

commercial PC-based systems have become available that provide expanded field display capability; these

might be useful in future tests.

6.4.3 Combined Experiment Calibration Sequences

The calibration sequences can be classified into three categories: automatic, manual, and external. The

sequences are performed at various time intervals to provide information necessary to compute

measurement accuracy. Specific procedures are defined that the test engineer must undertake in order to

perform the calibration sequences.

1. Automatic calibrations are those initiated by the test engineer in the test shed to automaticallyinvoke

the calibration sequence and cause data channels to measure calibration data Automatic calibrations are

used to calibrate the most sensitive channels (those that require the highest measurement tolerances). They

45
TP-4655

are usually conducted immediately before and after a dataevent and are directly recorded to the 14-track

data tape. There is not enough time to process the results of these calibrations during data acquisition

because the objective is to get the calibration sequences as close as possible in time to the actual data

event. The four types of automatic calibrations performed in the Combined/Unsteady Aero Experiments

are shown in Table 6-6.

Table 6-6. Automatic Calibration Procedures

procedure Description

A1 PCM 2&3 high and low shunt calibration

A2 Strain gage slow rotations

A3 Pressure system ramp calibration

A4 Pressure system short-line zero

calibration

Calibrate

Offset

Offset

Slope

Offset

2. Manual calibration requires the test engineer to set up and conduct the calibration in the field on the

transducers in situ. These calibrations should be performed within the specified time intervals. These are

done using the Quick-Look system, and all data are saved as PC data sets in units of raw counts. Two

sets, a pre- and a post-calibration, need to be done for each affected channel before fmal accuracy values

can be specified. The manual calibration procedures and recommended time intervals are shown in

Table 6-7.

3. Extemai calibration requires the transducer to be removed and calibrated in the calibration lab or in

the wind tunnel. These calibrations require more effort and are typically done on channels that are very

stable or require less measurement tolerance and do not need frequent calibration. The calibration results

are worked up to ensure that all measurements are within the required accuracy. Two sets, a pre- and

post-calibration, need to be done for each transducer before final accuracy values can be specified.

External calibration procedures are shown in Table 6-8. .

Table 6-7. Manual Calibration Procedures

Procedure Description Frequency Calibrate

M1 PCM 1 north MET electronics < 1 week Offset

, M2 AOA transducers < 1 week Slope & Offset

M3 Blade pitch angle < 1 week Slope & Offset

M4 Machine yaw angle potentiometer < 1 month Slope & Offset

M5 Blade azimuth angle potentiometer < 1 month Slope & Offset

M6 VPA wind directions < 1 month Slope & Offset

M7 VPA wind elevations < 1 month Slope & Offset

M8 Blade pulls for blade strain gages < 1 month Slope

M9 Tower pull for tower strain gates < 1 year Slope & Offset

M10 Yaw pull for yaw moment < 1 year Slope & Offset

46
TP-4655

Table 6-8. External Calibration Procedures

Procedure Description Frequency Calibrate

E1 Anemometer calibrations in wind tunnel < 1 year Slope

E2 Differential pressure sensor in calibration lab < 1 year Slope

E3 Absolute pressure sensorin calibration lab < 1 year Slope

E4 Differential temperature sensorin calibration lab < 1 year Slope

E5 Absolute temperature sensorin calibration lab < 1 year Slope

E6 Powertransducers in calibration lab < 1 year Slope

The recommended frequency of calibration intervalsis to be used only as a guide. The stated intervals

are based on test experience to provide required accuracy values. Exact timing is not critical because

calibrating at these intervals does not guarantee data accuracy. What is importantis to performpre- and

post-calibrations. It should be the objective of the test engineerto see that all channelsare pre- and postcalibrated at appropriate times as close as possible to when experiment data events are recorded.·

6.4.4 Field Data Recording and Processing Requirements

A data event consistsof 10 min of recorded data, during which all required parameters are measured. It

is boundedby calibration sequences designedto ensuredata validity. Allinformation necessary to conduct

requiredcalibrations is recordedso that calibration sequences can be reproduced. It is most preferable to

directly record raw PCM count data coming from channels during calibration sequences. From these,

count to engineering unit conversions are derived. Each 14-track tape should contain two data events,

preceded and followed by the appropriate automatic calibration sequences as defined in Table 6-9.

Calibrations 8 through 11 are optional if events 1 and 2 are done within an hour. The overall objective

is for all channels of each data event to have a pre- and a post-calibration sequence recorded on tape.

Over a longer term, manualand externalcalibrations shouldbe performed in a timely fashionto maintain

data base calibration coefficients up to date and to guarantee data accuracy. A hypothetical schedule is

shown in Table 6-10 that assumes an experiment conducted over a 6-monthperiod in which various sets

of data events are collected. The pre- and post-calibrations should be performed as close to the data

eventsas practical. All data are recordedon the Quick-Look systemand calibration coefficients generated

according to prescribedmethods. Some of the intermediate calibrations could be omittedif data sets are

recorded close enough together in time.

All information necessary to generate calibration coefficients for all measured channels is available to the

test engineerin the field. The calibration procedures are Performed by the test engineer at required time

intervalsto providethe information necessary to assessdata accuracy and to determine if the data sets are

valid or need to be re-acquired. The test engineer can work up the data at any convenienttime after a

data event or tape has been collected.

In addition to conducting calibration, other methods have been devised to ensure that critical data

measurements are valid. These methods depend entirely on the channels being measured and the .

availability of built-inredundancy or cross-checking measurements. For example, to ensurethat the VPA

anemometers are functioning correctly, we have found that long-termaverages to check horizontal wind

stratification will readily pinpointout-of-calibration anemometers. For verifying pressuremeasurements,

we have wind tunnel data from three independent sources in whichpressuredistributions as an AOA

47
TP-4655

Table 6-9. Event Acquisition Procedure

# Type

1. A1

2. A2

3. A3

4. A4

5.

6. A4

7. A3

8. A2

9. A1

10. A1

11. A2

12. A3

13. A4

14.

15. A4

16. A3

17. A2

18. A1

. Description

Pre-PCM 2&3 high and low calibrations

Pre-slow rotations

Pre-pressure systems ramp calibration

Pre-pressure system zero calibration

Post-pressure system zero calibration

Post-pressure system ramp calibration

Post-slow rotations

Post-PCM 2&3 high and low calibrations

Pre-PCM 2&3 high and low calibrations

Pre-slow rotations

. Pre-pressure system ramp calibration

Pre-pressure system zero calibration

Post-pressure system zero calibration

.Post-pressure system ramp calibration

Post-slow rotations

Post-PCM 2&3 high and low calibrations

Time

< 1 hour prior to event 1

< 1 hour prior to event 1

Immediately prior to event 1

Immediately prior to event 1

Event 1:10 min of run data

Immediately following event 1

Immediately following event 1

< 1 hour after event 1 (can sub 10 or

17)

< 1 hour after event 1 (can sub 9 or

18)

< 1 hour prior to event 2 (can sub 1

or 9)

< 1 hour prior to event 2 (can sub 2

or 8)

Immediately prior to event 2

Immediately prior to event 2

Event 2:10 min of run data

Immediately following event 2

Immediately following event 2

< 1 hour after event 2

< 1 hour after event 2

Table 6-10. Six-month Experiment Acquisition Procedure

# Type Description Time

1. E1 Pre-wind tunnel calibrations Up to 2 months before experiment

2. E2-E6 Pre-calibration lab transducer calibrations Up to 2 months before experiment

3. M9, M10 Pre-tower and yaw pull calibrations Up to 2 months before experiment

4. M4-M8 Pre-event set #1 in situ transducer calibrations Up to 2 weeks before event set #1

5. M1-M3 Pre-event set #1 critical calibrations Up to 3 days before event set #1

6. 1 week of Data Events set #1 (See Table 6-9)

7. M1-M3 Post-event set #1 critical calibrations Up to 3 days after event set #1

8. M4-M8 Post-event set #1 in situ transducer calibrations Up to 2 weeks after event set #1

9. M4-M8 Pre-event set #2 in situ transducer calibrations Up to 2 weeks before event set #2

10. M1-M3 Pre-event set #2 critical calibrations Up to 3 days before event set #2

11. 1 week of Data Events Set #2 (see Table 6-9)

12. M1-M3 Post-event set #2 critical calibrations Up to 3 days after event set #2

13. M4-M8 Post-event set #2 in situ transducer calibrations Up to 2 weeks after event set #1

n-2

n-1

n

M9, M10

E2-E6

E1

Post-tower and yaw pull calibrations

Post-calibration lab transducer calibrations

Post-wind tunnel calibrations

48

Up to 2 months after experiment

Up to 2 months after experiment

Up to 2 months after equipment
TP-4655

function are documented We have found that pressure dismbutiondata binned according to the AOA

is a good way to validate pressure measurements. These and other techniques are built into various

processing routines that are used to check and verify critical measurements.

6.4.5 Comprehensive Data Postprocessing

As stated above, final channel accuracy values cannot be calculated until all post-event calibration

procedures have been performed and processed. All post-calibrations should be performed as soon as

possible afterthe experiment has been completed Forthat reason, it is especially important to remove

anemometers or other transducers so that they are not damaged if they cannot immediately be postcalibrated. After post-calibrations, resultingmeasurement accuracies for all channelsshould be calculated

and incorporated'into thechannel data base for use in subsequentcomprehensive postprocessing analysis.

Many subsequentprocesses are appliedto the data sets duringthepostprocessing phase. All channel data

are reduced to sample rates, shown in Appendix C, by decimation and filtering. This requires the use of

variouscomputersystemsand softwarepackages,as shownin Figure 6-8. These proceduresare described

further in other reports and are summarized below:

1. Record PCM streams and time code to I4-track analog tape.

2. Perform Quick-Look display and analysis in the field

3. Generate calibration coefficients for all channels using Quick-Looksystem.

4. Associate and assemble appropriate calibrationcoefficientswith each channel for each Io-min data

set

5. Make two passes through the NREIlFairchild-Weston PCM Telemetry Data Reduction System to

reduce and combine PCM streams into two groups of three streams each; output binary data sets to

digital 9-track tape.

6. Load digital tape stream sets into UNIX system.

7. Use custom UNIXlCsoftwareto combinetwo groupsof three streamseach into one continuoustime

series that contains all six streams combinedto I-msec precision.

8. Use custom·UNIXlC software to

a. Convert counts to engineering units

b. Convert multi-rate data to common rate of 1.92 msec (520.83 Hz)

c. Generate secondary derived parameters

d Smooth azimuth angle signal for azimuth averaging

e. Store data sets to optical media.

9. Use GENPRO'to

a. Low-pass filter all channels to 4O-Hz bandwidth

b. Low-pass filter all channelsto Io-Hz bandwidth

c. Low-pass filter all channelsto I-Hz bandwidth

d, Interpolate and smooth low-rate data to higher rates

e. Generate power spectra for selected channels

f. Generate statistics for all data sets.

49
TP-4655

10. Use PC-based data base (File Express) on PC-NFS network to maintajn,summary statistics data base

of selected channels from all processed data sets and provide on-line access for other users.

11. Provide data sets on optical media data base for analysis by other users.

6.4.6 Dynamic Effects

All calibrations and datapostprocessing methods are designed to verify the accuracy ofsteady-state data

measurements. Other considerations that result from the effects of the dynamic response oftransducers

also affect data accuracy. These are difficult to assess and cannot be measured directly from the abovedescribedcalibration procedures. Basedon previous test experience, we have estimated thatmeasurements,

may be susceptible to accuracy deficiencies because ofdynamic effects and have identified them in various

reports. Oneofthe objectives of conducting these types of experiments is to discover and document such

potential sources of error. Further postprocessing analyses may also reveal other areas that need to be

considered. This information will be useful in designing future tests and providing fleld-basedmeans for

identifying problems and conducting calibrations.

Two major areas of concern associated with dynamic effects were originally identified and addressed

during experiment planning. F.1!St was the dynamic frequency response ofthe pressure system. An "organ

pipe" effect could exist in the tubing needed to connect pressure transducers to the surface tapes. This

would cause gain amplifications and phase effects that occur as a function of frequency and tube length.

Special test apparatus were developed to measure the actual dynamic response ofthe system. ID. addition,

Akins (1987) used an independent system to measure and document the effects. Results showed that no

significant phase or gain effects were evident given the configuration of the system up to frequencies of

80 Hz. Because all processed data sets show no appreciable pressure information above 40 Hz, we have

concluded that the frequency response of pressure system measurements are valid

The second source of potential dynamic effect error is aliasing. Aliasing is inherent in all digital data

processing that is preceded by analog-to-digital conversion. Aliasing errors are a function of sample rate

and filter set point. In the CombinedlUnsteady Aero Experiment tests, data channels are sampled at

various rates, depending on required bandwidth, and are anti-alias filtered with 4-pole low-pass

Butterworth analog filters (see Appendix C). For all channels on a givenPCM stream, the sample rate is

dictated by the channel(s) with the maximum required bandwidth. All channels are over-sampled by at

least a factor of 5 over the required bandwidth. Factor of 5 over-sampling, in conjunction with 4-pole

Butterworth anti-alias filters, results in an RMS aliasing error of 2%. Lower-bandwidth channels, which

are further over-sampled, have even smaller errors. For example, pressure measurements are anti-alias

filtered with a 4-pole l00-Hz Butterworth filter and sampled at 520 Hz. This results in aliasing errors that

are less than 2% in the range of 0- to l00-Hz bandwidth. In reality, there is very little pressure

information above 40 Hz, and resulting aliasing errors in this range are less than .1% (Strock, 1983).

One additional source of dynamic error may exist in prop-vane measurements. Analyses conducted to

study differences between prop-vane and sonic anemometersindicate that wind-speed measurements made

in turbulent conditions in the wake of a wind farm may show significant dynamically induced errors.

These effects are currently under study, and it is not known if the turbulence at site 3.3 would produce

similar effects.

50
TP-4655

North Vertical Local Strain/ 30t & 63%&

Met. Plane Metl SO% 47% Pressure

Tower Array Turbine Pressure Pressure & AOA's

11 2

1

3

1

4 Is 1

9

PCM Data streams

•

14-Track

Analog

Tape

Playback

PCM Data Streams

-

PC Quick-Look~--------~

System

Setup

Files

(cals)

QuickLook

Data

Display

Data

verification

PCM Data Reduction: - 1/2 Tape speed (15 ips) - 5-minute record blocks - 2-pass process - output digital values

Fairchild/Weston

PCM Telemetry

EXPERT System

Data Archive:

- Raw binary integers: - 234 Channels - 93,444 samples/sec - 11.2 Mbyte/min

Combine I------t Processi---tf------foptical

Data Data Archive

Pass 1 passl2

PCM 4,8,1 PCM 9,2,3

9-track 9-track

tape tape

I

MASSCOMP

UNIX

System

Intermediate

Data Storage/

Transfer

I

Figure 6-8. Combined experiment phase II data processing plan

51
TP-4655

7.0 Wind Tunnel Testing

Wind tunnel data were used as reference data sets to compare with wind turbine data because this is the

type of datathat is used by designers as input to performance and structural design codes. For this reason,

it was important to have an extensive data base for all operating conditions tested in the field. It was also

important that this data base correspond to the exact airfoil under test. The wind tunnel data should

represent the same chord, Reynolds number range, AOA range, pressure tap locations, and surface

imperfections. Unfortunately, meeting all these criteria with one dataset measured from one wind tunnel

was not possible. For this reason, several wind tunnel tests were run; each one satisfied a different aspect

of the required reference data set These different wind tunnel test programs are described in this section.

The airfoil chosen for the Combined Experiment was the S809, as mentioned earlier. This airfoil was

chosen because;it was developed specifically for wind turbine applications, there was a wind tunnel data

base available from the Delft wind tunnel in The Netherlands, and NREL had extensive airfoil design

analysis results from the Eppler design code (Somers, 1989).

7.1 DELFT Tunnel Tests

. .

The objectives of the Delft wind tunnel tests were to confirm the analytical design of the airfoil and to

calibrate the analysis code used to perform the design. To meet these Objectives, an extremely accurate

600.Q-mm (23.6-in.) chord model was fabricated from aluminum and buffed to a surface finish thatwas .

within 0.1 mm (0.004 in.) of the specified airfoil coordinates. Pressure taps were staggered on upper and

lower surfaces at 108 locations. This level of model accuracy was necessary for model validation but was

not practical for operating field tests on the Combined Experiment rotor. Butterfield (I989a) describes

the differences between the accurate Delft model and the model used in field tests and in Ohio State

University wind tunnel tests.

Appendix D contains a summary of Somers (1989). This summary includes a brief description ofthe test

setup and a subset of the total results from these tests.

7.2 Ohio State University (OSU) Wind Tunnel Tests

Airfoil test data can be affected by surface irregularities, pressure tap locations, trailing edge accuracy, and

many other test setup details. It was important that the reference data set represent the exact airfoil and

instrumentation configuration, so that differences detected between the rotating blade data and the wind

tunnel data could be attributed·to rotating blade effects. It was also important to establish an unsteady

(dynamic stall) reference data set

For these reasons, a second series of wind tunnel tests was conducted. These tests used a 2D model that

was fabricated using the same molds used to make the test blade. This assured that the same surface

irregularities, trailing edge accuracy, chord length, and pressure tap locations would exist on the wind

tunnel test model. The same pressure measurement instrumentation was used in the wind tunnel as on

the test turbine. The same AOA probe was used during these tests to assure any effects of the probe

would be included in the reference data sets.

The OSU wind tunnel was an open-eircuit type with a .92 m x 1.5 m (3 ft x 5 ft) testsection. The model

had a O.46-m (I8-in.) chord length and spanned the O.92-m dimension of the tunnel. The pressure tap

locations and pressure measurement instrumentation used was the same as that used on the Combined

52
TP-4655

EXperiment rotor that was described earlier. Appendix E contains a description,of the test setup arid

results from this test program.

7.2.1 Steady Tests

Constant wind-speed tests were run for Reynolds numbers rangingfrom 1,000,000 to 2,000,000. During

these tests, pressure measurements were recorded.and integrated using the method described by Rae and

Pope (1984)~ The AOA probe was calibrated at the same time by recording the airfoil geometric angle

and the flag angle'on the probe simultaneously. The discrepancy between thetwo angles was assumed

to be due toupwash, as described in Section 5.2. Because oftunnel blockage effects, the AOA range was

limited to '20 deg. A Pitot tube was used to measure the total drag using the wake momentum deficit

approach described by Rae and Pope (1984).

The results of these tests agreed with the Delft data in general. Figure 7-1 shows a comparison of lift

coefficient data from all three wind tunnels. The slope ofthe OSU data is 12% greater than the Delft data

for AOAs less than 5 deg. ' The maximum lift coefficient (CL(max» is 8% less than the Delft data.

Regardless of the small quantitative differences, the qualitative differences. were judged to be reasonable

for the purposes of this test program. These differences could be due to model differences and wind

tunnel differences. The pressure distributions appeared to be quantitatively and qualitatively similar in

terms of the stall progression and pressure profiles.' Comparison pressure distributions shown in

Appendices D and E demonstrate the similarity. For this reason it was felt that the OSU data represented

the Combined Experiment airfoil better than the Delft data, but both would be used for comparisons with

rotating blade data.

7.2.2 Unsteady Aerodynamics Tests

Because wind turbines operate in an unsteady aerodynamic environment, an unsteady aerodynamic

reference data base was required. The OSU wind tunnel dynamic stall tester was used to oscillate the

1.2

1.0

0.8

0.6

----Q)

0 0.4

U

......

-- 0.2 :.:i

0.0

-0.2

-0.4

-5

[3B8B€] Delft Data Re= 1 million

GeeeE) OSU Data Re= 1 Million

CSU Data Re=650.000

o 5 10 15 20

Alpha (degrees)

Figure 7-1. Wind tunnel data comparison

S3
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model AOA in a sinusoidal manner. Various amplitudes and frequencies of oscillation were tested, and

the results are described in Appendix E.

7.2.3 Rough Airfoil Performance

Stall-controlledwind turbines suffer performance losses when the blade leading edges accumulatedebris

from insect impacts and airborne particulates. To document the sensitivity of the S809 to leading edge

roughness, buildup tests were conducted at OSU. Appendix E describes steady and unsteady airfoil

performance tests with roughness added to the leading edge of the model. The results of these tests

provided a reference data set for the rough blade tests conducted on the Combined Experiment turbine.

The results of these tests are discussed in section 8.0.

7.3 Colorado State University Wind Tunnel

The Delft and OSU test data were limited to AOAs less than 22 deg and 20, respectively. Blockage

effects beyond these angles resulted in unacceptable errors. The Combined Experiment was focused on

stall and deep stall airfoil performance that occurs at AOAs from IS to 30 deg. For this reason, an

additional wind tunnel test was conducted at the Colorado State University (CSU) Environmental Wind

Tunnel. Thelarge 3.66 m (12 ft) x 1 m (39 in.) test section availablein this tunnel significantlyreduced

the blockage effects during high AOA testing.

7.3.1 Wind Tunnel Test Setup

The CSU Environmental Wind Tunnel was originally designed for studying flow over models of cities

and buildings. The test section was reduced to 3.66 m (12 ft.) x I m (39 in.), which allowed a I-m airfoil

test section to be inserted across the narrow dimension. This resulted in a wide test section that would

minimize the blockage effects. The solid blockage was 0.28% using Thom's method (Rae and Pope,

1984). Figure 7-2 shows the general layout of the tunnel and the modifications that were made for this

test. The modified,open-circuittunnel was capableof a maximumvelocityof 27 m/sec (a8 ftlsec), which

resulted in a Reynolds number, based on the 0.46-m (1.5-ft) chord, of 650,000. This Reynolds number

value is lower than the HAWT test conditions of 880,000 at the 80% blade span, but it was felt that

previous wind tunnel data would accuratelydescribe the airfoil performancefor Reynolds number values

from 750,000 to 3 million for AOA values less than 20 deg. Pressure distribution measurements were

made on the model along with pitot tube measurements 2 chord lengths displaced from each side of the

model and 1 chord length upwind of the model leading edge. Tunnel temperature, probe total pressure,

local flow angle at 0.6 chord ahead of the leading edge, and model pitch angle relative to the tunnel axis

were also measured.

Normally, airfoil drag is measured by measuring the velocity profile in the wake of the airfoil and then

equating the momentum deficit in that wake to the total drag. This requires a movable Pitot tube or a

wake rake positioned downwind of the airfoil. These measurements were not possible to make on the

rotating wind turbine blade. There is also evidence that this technique is inaccurate when large-scale

separationis present due to rotationalflow in the wake. Because NREL's focus was stall behavior, where

large-scale separationis always present, it was decided that only pressure drag (CDn> would be measured

BecauseCDp is determinedfrom pressure distributionintegrations(Rae and Pope, 1984),wind tunnel data

could be compared with HAWT data directly,

54
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----------~3 ..---------- -------17.42PI-------

T~st S~ctlon

T~"

0.30 PI ." .:"'."..:

PLAN

ELEVATION

a

---- Scale-, I"l

5

----'

Figure 7·2. Colorado State University environmental wind tunnel

Tunnel turbulence level was a major concern. High-frequency turbulence can affect the airfoil boundary

layer, which will affect the performance. To address this concern, a Pitot tube traverse test and a hot-wire

traverse test were conducted. The traverses were performed across the test section mid-span in the same

location as the model. The results of the first test, shown in Figure 7-3, describe a 6-cm (2.S-in.)

boundary layer at the tunnel wall and an acceptable flat velocity distribution across thetunnel. The results

of the second hot-wire traverse confirmed the location ofthe boundary layer. A value of 1% turbulence

intensity was measured at the mid-span of the test section. This is a high value for airfoil testing, but the

important consideration is the scale of the .turbulence. Ifthe scale is close to that of the airfoil boundary

layer, it can trip laminar flow into turbulent flow and thus modify performance. Ifthe scale is large, there

should be little effect Figure 7-4 shows a plot of the power spectral density (PSD) of the hot-wire data

at the tunnel mid-span at a tunnel speed of 24.5 m1sec (80 ftIsec) e : The PSD has been multiplied by

frequency and normalized by the standard deviation squared. The area under the curve is unity and

represents the measured turbulent intensity of 1%. Itis clear that the majority ofthe energy is below 1 Hz

(24-m scale). This scale ofturbulence is much larger than the boundary layer and therefore should have

minimal effect on the performance ofthe airfoil. These fluctuations were due to small changes in average

tunnel.speed control. -

The airfoil model was 99 em (39 in.) long with a chord of 45.7 em (18 in.). This model was the same

one used in the OSU wind tunnel tests described in section 7.2. It was placed in the wind tunnel, bridging

the narrow dimension (99 em). This allowed the wake of the airfoil to expand across the 3.67-m

dimension of the tunnel. A rubber seal was placed between the wall of the tunnel and the end of the

model to prevent leaks. The model was fabricated from the blade molds used to build the blades. This

was done to assure that the model would accurately represent the HAWT blade. Pressure taps were

installed inside the model using 25- to 38-cm-Iong, I-mm-inside-diam. stainless steel tubing. Each tube

led from the airfoil surface to a pressure transducer mounted inside the model. The 31 pressure tap

locations and installations were identical to the HAWT blade installation.

55

TP-4655

The model also included an LFA probe and a total pressure probe mounted on the leading edge

(Section 5.2). A 5-cm-(2-in.)-long, lightweightfiberglass flag was used to sense local flow angles. The

same probe was mounted on the HAWT blade. To accurately account for the induced upwash effect on

this LFA probe, measurements were taken during the wind tunnel tests and compared with previous

measurements made at a Reynolds number of 1 million. Section"5.2 describes the LFA probe and

previous calibration measurements of this probe in the OSU wind tunnel.

Each data channel was filtered with a roll-off frequency of 100 Hz and then sampled at'520 Hz using a

PCM encoder. The PCM stream was recorded on a Honeywell 101 tape recorder and later decoded and

analyzed. The pressure system instrumentation and recording equipment is described in detail in

Section 5.1.

7.3.2 Data Analysis

The wind tunnel data were steady and therefore needed no special processing. Pressure measurements

were normalizedby local tunnel dynamicpressure to get pressure coefficients (CP>. Pressure coefficient

distributions were integrated around the airfoil to obtain values of normal force coefficient(CJ, tangent

force coefficient (Cr), and pitching moment coefficient (Cm). These were used along with AOA

measurements to calculate.lift and pressure drag coefficients (CL, Cop>, using the method described by

Rae and Pope (1984).

7.3.3 Wind Tunnel Results

A comparisonof CLdata recordedfrom the three differentwind tunnelswas made first to establisha baseline validity check on the CSU windtunnel data. As can be seen from Figure 7-1, the curves do not all

look exactly alike. The Reynolds numbers for all three are not the same, which could be one of the

explanations, but in general the-comparisonis reasonable. The slope of each curve is approximately the

same, the zero lift angle is similar, and CL(max) is similar but decreasing with ttW Reynolds number.

Figure 7-5 shows how CL(max) decreases with the Reynolds number and comparesthe general trend with

the NACA4412 and NACA 64-418 airfoils. This comparisonshowsthat it is reasonableto expect a drop

in CL(max) in the CSU data because of the Reynoldsnumber. Additional data will be presentedin Section

8.0.

From these comparisons, it was felt that the CSU data did not match previous wind tunnel data perfectly,

but they were the best to use in HAWT comparisons becausetheyrepresentedthe performance of an exact

copy of the airfoil and instrumentation of the HAWT blade. Any differences betweenthis set of data and

the HAWT data wouldmostlikely be due to real differences occurring between2D windtunnel conditions

and 3D wind turbine aerodynamics. The CSU data also containedvalues of AOA up to 90 deg. Previous

wind tunnel test data only had values up to 20 deg. High values of AOA were needed to compare deep

stall HAWT data to wind tunnel data. Figure 7-6 shows the results of the high AOA datafor a tunnel

speed-of 26 mlsec (88 ftIsec) and a Reynolds number equal to 650,000.

Appendix F through Appendix L contain the completeresultsfrom the CSU wind tunneltest The results

include C, C1" lift, pressure drag, CL, CDP' CM, and pressuredistributions. 'Three tunnel speeds were run

corresponding to Reynolds numbers of 350,000, 500,000, and 650,000.

57


TP-4655

8.0 Rough Airfoil Performance Tests

8.1 Background

Blade surfaceroughness has been observed to decrease the efficiency of stall-controlled windturbines by

as much as 40% (Yekutieli and Clark, 1987). Most of the degradation can typically be attributed to

premature stalling of the airfoil, which lowers the maximum lift coefficient Figure 8-1 illustrates the

effect this can have on stall-controlled rotors. It shows a dramatic difference in the peak power

performance for an Enertech 6Q-kW wind turbine before and after a rain shower. A smaller decline in

rotor performance caused by leading edge roughness is experienced at lower AOAs, which can be a

significant factor in determining energy capture for pitch-controlled wind turbines (Holtz, 1988).

70.---------------------,

60

50

o '([0-00-

,.

C? C!.9 C!.9 Clean Blades .;0

~Unclean Blades 0"0

•

9'

?

18 20

o

8 10 12 14 16

Wind Speed (m/s)

l'

r?

d

/

QlD ° /

6

O-+----r--~-__r--.___-_._-__r--.,._---i

4

10

20

L..

(l)

30 o

0...

Figure 8-1. 6o-kilowatt HAWT performance

Leading edge roughness on wind turbine blades is a universal problem that affects virtually every

configuration of wind turbine. It has contributed significantly to producing lower energy, fouling wind

turbine control algorithms, and making loads more difficultto predict Traditional airfoils, such as the

NACA44XXor 23XXX, are beingdiscarded by wind turbinebladedesigners as they becomemore aware

of the high degree of roughness sensitivity that these airfoils have. Newer airfoil designs such as the

NREL airfoil families and the LS-l series from the National Aeronautics and Space Administration are

becoming more popular largely because of their relativeinsensitivity to roughness.

The effectsof roughness on airfoils are most commonly inferredby examining the influence on the rotor's

power curve. This method is accurate and reliable for determining the impact on energy capture for a

60
TP4655

specific HAWT configuration, but it does not provide much information about changes to the aerodynamic

properties of the airfoil. Wind tunnel tests may be used to predict performance degradations caused by

roughness in the sub-stall regions, but stalled airfoil behavior is radically different on a rotating blade.

The problem is that the stalled airfoil performance on a rotating wing is modified by 3D flow effects

(Madsen, Rasmussen, and Pedersen, 1988). It is common for wind turbine designers to underestimate

peak performance and loads using wind tunnel airfoil data. Measurements taken directly off the rotating

airfoil are the only accurate way to completely determine the effect of roughness on airfoil properties.

8.2 Roughness Description

Most airfoil roughness problems experienced by HAWTs have been caused primarily by insects

accumulating on the surface near the leading edge ofthe blade. The distribution is generally non-uniform,

with larger particle sizes and particle densities distributed near the leading edge, rapidly declining toward

the trailing edge. In general, particle size usually increases and particle density decreases when

progressing from the tip toward the root 'of the blade.

The NACA standard roughness was created to simulate the typical roughness distribution experienced by

aircraft, This standard consists of a uniform distribution of particles between the leading edge and the 8%

chord line on the upper and lower surfaces of the airfoil (Bragg and Gregorek, 1989). Particle size is

defined by the non-dimensional ratio of the particle diameter (k) divided by the chord length (c). The k1c

value for the NACA standard roughness is .00046, which corresponds to grit sizes of .21 mm (.0083 in.)

for the Combined Experiment rotor.

Operating conditions for wind turbines are quite different than for aircraft, however. Wind turbines

operate closer to the ground and at lower Reynolds numbers and are cleaned less frequently.

Consequently, the NACA standard roughness is not severe enough to represent the actual accumulation

ofinsects observed by the authors. In order to do a realistic test ofrough airfoil performance on the S809,

it was necessary to create a roughness Pattern that was more appropriate for wind turbine applications.

A "simulated insect" roughness was developed and applied to all three blades over the outer 3.35 m

(11 fi). Coarse grit particles ranging in size from 0.5 to 1.0 mm (.020 to .040 in.) were distributed onto

a 20.3-cm-wide (8-in.) strip of 3M #444 double-coated tape, 0.05-mm thick, that was centered on the

leading edges of each blade. The grit was scattered randomly by dropping it onto the leading edge tape

from above while the blade was horizontal with the leading edge positioned upward This created grit

patterns of.varying density that approximated the natural accumulation of insects and dirt on the blades.

Grit densities were highest at the leading edge where 62 particleslcm2 (400 particlesJin2.) were counted

and dropped off to zero particles near the aft edge ofthe tape. A photograph ofthe roughness distribution

used is shown in Figure 8-2. The resulting k1cvalues ranged from .0011 to .0022, or roughly 2 to 4 times

the NACA standard roughness size. Although the grit densities tapered offtoward the trailing edge, some

grit particles were scattered back as far as 20% chord

Particle size and placement on the low-pressure surface of the airfoil are the two leading factors in

determining the severity of roughness (Bragg and Gregorek, 1989). When compared to NACA standard

roughness, the NREL roughness distribution was more severe. This was an important factor in comparing

the data from this test with other airfoil data.

61
TP-4655

Figure 8-2. Roughness distribution on leading edges of test turbine blades

8.3 Roughness Testing

All the wind turbine roughness testing was conducted during Phase I of the Combined Experiment in

May 1989. Windtunnel roughness tests were conducted at CSUin September 1989. Windturbine tests

wereconducted over windspeeds ranging from5 m1sec (11.2 mph) to 30 m1sec (67.1 mph). Rough rotor

data of 3.5 h wererecorded. Electrical power, shafttorque, andnineprop-vane anemometer signals were

the primary signals used for the performance comparisons; however, the active pressure, bladeload, and

inflow signals were used to determine the aerodynamic effects of roughness on the airfoil. Most of the

analysis and data reduction techniques used follow the procedures described in the previous sections, but

some small changes were introduced for simplicity. The interested reader is referred to Musial,

Butterfield, and Jenks (1989) and Musial and Butterfield (1990).

8.4 Rough Performance Results

A fifth-order polynomial was fit through each data set of rough and smooth data to obtain an accurate

evaluation of the roughrotorperformance effects. Thesecurves are compared in Figure8-3 from 5 m1sec

(11.2 mph) to 22 m1sec (49.2mph). Bothcurves have approximately the sameShape, but the rough data

62
TP4655

25~----~-~---------------------,

_ _ Measured Rough Data ( Curve Fit )

. Measured Smooth Data ( Curve Fit )

IJ-&+oEHI PROPPC ( OSU Smooth wr Data )

20

10 15 20 "25 30 35

Wind Speed (m/s)

5

O-t----~--___r---____.---....,._---.,...._--__..,.....---_1

o

L.-

G)

3:

o 10

(L

5

Figure 8-3. Combined experiment wind turbine performance

curve is about 10% lower than the smooth data curve for most of the low to moderate wind speeds. At

about 15 mlsec (33.6 mph), the two curves converge, and at 19 mlsec (42.5 mph), they cross.

Another way to look at this degradation is shownin Figure 8-4, where two normalized power curvesare

plotted on the same graph. Both are plots of rough rotor performance normalized againstsmooth rotor

performance for the range of windspeedstested. A valueof 1.0on this curve wouldindicate no effective

change caused by roughness. The percent of degradation caused by roughness is greatest at low wind

speedsfor these curves. Asindicated, one curve is mechanical power, and one curveis electrical power.

Because data for these two curves were measured using independent transducers, their agreement is

presented here to validate the accuracy of the measurement

In Figure 8-3,the measured roughand smoothmechanical powercurvesare also compared to a predicted

power curve that was generated using PROppe performance code with 2D lift and drag data. Lift

coefficients from the OSU wind tunnel tests that were used to generate the predicted power curve are

shown in Figure 8-5. The smooth measured data match the analytical predictions very closely until

approximately 15 m1sec (33.6 mph), wherethe analytical power curves reach a maximum value at about

15 kW and begin to roll off. The measured smooth power curve continues to increase beyond 18 kW

without leveling off. At low wind speeds below 15 mlsec (33.6 mph), the smooth, predicted curves

exceed the rough data, as expected. As seen previously in Figure 8-4, the rotor experiences an average

63
TP-4655

1.1

(1) 1.0

3:

o

0.. 0.9

...c

+-'

o

E0.8

(f)

<, 0.7

(1)

3:

o

0.. 0.6

..... --------------------- K

...c

01

::J 0.5

o

0:::

...- - Generator Power

• • • • • Mechanical Power

0.4

10.00 15.00 20.00 25.00

Windspeed M/S -

0.3 -t-----.------r--------,.-------1

5.00

Figure 8-4. Normalized power output--combined experiment

decline of 10% in power production because of the leading edge roughness, but the rough and smooth

measured power curves diverge from the predicted curve and continue to increase without reaching an

upperlimit. 'This is a familiar problem thatrelates to the stall characteristics of windturbines ratherthan

a roughness phenomenon. '

The effects of roughness on the Combined Experiment windturbine were examined aboveby comparing

roughand smooth powercurves. It is clearthatroughness had a negative effectoilperformance overmost

of the operating range, but this rotor did not experience the drop-offin peak power that is usually seen

on stall-controlled rotors. It was not clear what caused this effect.

'This windturbine differs from mostcommercial stall control windturbines because of its constant chord,

zero-twist rotor. Therefore, muchof the inboard sections of the rotor operate in the stall region even at

low to moderate wind speeds. Much of the peak power performance is dictated by the deep stall

characteristics of the airfoil and not by the low AOAsection properties (AOA = 0-10 deg). In order to

understand what is happening on this rotor, it is necessary to look at the stalled airfoil properties.

8.5 Rough 5809 Airfoil Characteristics

To studythe effect of roughness on airfoil properties, aerodynamic pressure measurements taken at 80%

span were used. Figure 8-6 shows the rough and smooth C1 versus AOA curves for the rotating (wind

turbine) and non-rotating (wind tunnel) cases out to 25-deg AOA. All four curves are in goodagreement

for very low AOA (0-3 deg). At 3 deg the roughdata for both the 2D and 3D casesbeginto drop off

64
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1.2 -r------------------------.

5 10 15 20

of Attack (degrees)

.......... OSU Wind Tunnel Data

-0.4 T-.;t----...----r------r---~---~

-5 0

Angle

-0.2

-+-J

C

(1) 0.6

U

:::= 0.4

(1) .

· 0

U 0.2

1.0

0.8

Figure 8-6. S809 OSU wind tunnel data

from the smooth airfoil curves. The two rough and the two smooth curves continue to maintain reasonable

agreement, respectively, until 11 deg, where the rough 2D datareach a peak of .73 and drop to about .63,

but the rotating data flatten out at about .75.

Meanwhile, both of the smooth data curves continuously increase monotonically through about 15 deg.

The smooth wind tunnel data stalls abruptly at 17 deg after reaching a CL(mu) of .96. This would be

expected from previous static tests. The rotating smooth data reached its peak at about the same AOA

but did not drop off, exhibiting delayed stall characteristics.

Although the smooth wind tunnel data stall sharply at 17 degt the rough wind tunnel data recover

unexpectedly from the drop-off measured between 11 and 16 deg and increase to a CL(mu) of about .98

at an AOA of 18 deg. This secondary peak is sustained until 2O-deg AOA where it decreases back to a

value of CL(mu) near 0.7. The secondary peak experienced by the rough wind tunnel data actually

exceeded the smooth airfoil performance but at a higher AOA. One probable explanation is that the added

boundary layer turbulence, induced by the leading edge roughness, caused energy from the outer flow to

be introduced into the boundary layer. This added energy modified the boundary layer velocity

distribution, resulting in a delayed separation. This would account for the higher CL values measured

It should be noted that this secondary recovery peak in the rough wind tunnel data was only present at

a Reynolds number of 650,000.

65
TP-4655

1.0

0.8

-+.-J

C

Q)

.-

.U q.6

'+-

'+-

Q)

o

UO.4

-+-'

'+-

0.2 00000 CL CSU Smooth ••••• CL CSU Rough

......... C, Rotating Rough Tape55

.t&AAAA CL Rotating Smooth Tape20

0.0 +-----,.---.----,.---..,...-----l

o 5 10 15 20

Geometric Angle-of-Attack

25

Figure 8-6. Comparison of rough and smooth CL data from rotating and

nonrotating airfoil tests

At higher AOAs, near 20 deg, the smooth rotating CLvalues are sustained at levels about equal to the

rough rotating airfoil data. However, notethat it is even moresignificant than the effectof roughness for

both the rough and smooth rotating data curves, where they exceed the smooth wind runnel CLdata by

25% because of delayed stall.

The effects of roughness on maximum lift coefficient are seen in Figure 8-7. For both the rotating and

non-rotating cases,roughness on the leading edge of this airfoil lowered CL(III8lt) by 22%. This decrease

in CL(mu) was greater than expected; however, when compared to data from other airfoils, the S809

roughness sensitivity effects were actually smaller. Figure 8-7 (Bragg and Gregorek, 1989)shows the

effect of standardNACAroughness on CL(mu) as a function of the airfoil thickness for the NACA44XX

and the NACA230XXairfoil families. The data point corresponding to the 22% changein CL(mu) for the

S809 airfoil used on the Combined Experiment rotor is included on this plot for comparison. It can be

seen that the S809 is a significant improvement over both NACAairfoils. It should be pointed out that

the roughness used to generate the data for the NACA airfoils was the standard NACA roughness. The

roughness used to test the S809 was the simulated insect roughness. As discussed earlier, the simulated

insects have klc values 2 to 4 times greater than the standard NACA roughness. On the NACA 0012

airfoil, Hoerner (1975)shows that this higher degree of roughness wouldhave doubled the reduction in

CL(mu). Unfortunately, the magnitude of CL(mu) change because of increasing roughness size was not

available for the airfoils in Figure 8-7, but the trend established by Hoerner (1975) wouldindicate that

rough performance improvements experienced by the S809 over the 44XX and the 230XX airfoils are

probably conservative.

66
TP-4655

0.6 ~-------------------

-+-'

c

Q) 0.5 e_

U

'+-

'+-

Q)

00.4

U

.......,

'+-

:..J 0.3

X

o

0°·2

-+-'

Q)

o

0.1

o

AAAAA. NACA 230XX Airfoil -Standard Rough a:a::E> NACA 44XX Airfoil -Standard Rough

I I I I I I SERI S809 Airloil -Simulated Insects

5 10 . 15 20 25

.Airfoil Thickness (percent)

Figure 8-7. Change in CL(max) caused by NACA standard roughness and airfoil thickness

. for typical wind turbine airfoils .

The rough and smooth CL versus AOA curves for the LS(I)-0413 airfoil (unmodified) from Bragg and

Gregorek (1989) are shown in Figure 8-8. As with the NACA airfoils in Figure 8-7, these data show the

effect of NACA standard roughness on the LS(l)-0413. From these data a 28% decrease in CL(max) can

be seen.

'This result is contradicted by other wind tunnel test data that have been presented for the LS(l) airfoils

as well as for the NREL airfoils (Somers, 1991; Miley, 1982, McGhee and Beasley, 1981; McGhee,

Beasley, and Somers, 1977). These reports indicate very small changes in airfoilperformance for the

LS(1) series and NIffiL airfoils when roughness was applied to the airfoil. However, all of these tests

were performed using only a smalllocaI disturbance at about .075 xJc to fix boundary layer transition near

the leading edge. This was much less severe than the wraparound roughness cases used at NREL and

OSU (NACA standard) and caused the roughness sensitivity characteristics to appear mild.

When comparing the data from Bragg and Gregorek (1989) with the S809 curves in Figure 8-6, it can be

seen that there is a slight improvement in roughness sensitivity for the S809 airfoil over the LS(l).

However, several cautions should be noted when comparing these two data sets. FlI'St, the LS(I) data

were taken at Reynolds number=3,000,000, but the S809 datawere taken at Reynolds number=650,000.

In Hoerner (1975), a lowering of the Reynolds number was shown to lower CL(max). However, when

standard NACA roughness was applied to the NACA 4412 and NACA 64-418 airfoils, the reduction in

CL(max) remained constant with a decreasing Reynolds number. It is probable that the LS(I) series will

be affected in the same way. Second, NACA standard roughness was used on the LS(l) tests but largersized, simulated insect roughness was used on the S809 tests. The effect ofroughness size was discussed

earlier. Finally, the LS(l)-0413 has a tic ratio of .13 compared to .21 for the S809. It is not known if

this difference in the airfoil thicknesses is significant

67
TP-4655

1.8

1.6

1.4

1.2

-+oJ

c 1.0

Q)

.-

0 0.8 .-

'+-

'+-

Q) 0.6

0

U 0.4

-+oJ

'+- 0.2 :....J

0.0

-0.2 (m:!)LS(1)-0413 Smooth - Re=3 Million

I •••• LS(1)-0413 Std Rough - Re=3 Million

5 10 15 20

of Attack (deg rees)

-0.4 ;-----r----,-----r---.-------I

-5

Figure 8-8. LS(1)0413 smooth and rough airfoil performance

No wind tunnel testing has been done on the modified LS(l) airfoils using realistic wind turbine

roughness, so it is not known how those airfoils compare to the S809.

8.6 Wind Tunnel and Rotating Comparisons of Rough Airfoil Data

Studying sectioncoefficients, such as CL in the abovediscussion, gives a more complete pictureof how

roughness changes the airfoil properties. In orderto understand the specifics of whatis happening on the

airfoils, it is necessary to examine the pressure distributions across the airfoil section. A complete

compilation of all the wind tunnel test pressure distributions is contained in Appendix H.

In Figure 8-6, there were at least three ADAs wheredistinctly different and interesting phenomena were

identified on the CL versusADA curves. At 11 degthe two roughairfoil curvesreach an initialmaximum

value; at 14 deg the rough curveshave droppedoff but the two smoothcurveshave reacheda maximum;

and at 18 deg the rough wind tunnel data have recovered butthe smooth wind tunnel data have stalled.

At each of these ADA cases, airfoil pressure distributions were plotted for each of the four curves in

Figure 8-6. These three pressure distribution plots are shown in Figures 8-9 through 8-11.

In Figure 8-9,the pressuredistributions are shown at about ll-deg ADA. At this angle, the rough wind

tunnel (solid circles in Figure 8-9) and rough wind turbine (solid triangles) data agree along the high

pressure or upwind side (lower curves in the figure). 1bey also agree from the leading edge to .40 x1c

on the low-pressure side (upper curves). From.4O x1c on the low-pressure side to the trailing edge, the

pressure distribution is characterized by a flat regionthat is causedby separation of the flow from the

68

TP-4655

-4-,----------------------,

-3

...

c

Q)

o

-2

Q)

o

U

Q)

::J -1

en

(J)

Q)

L.-

n,

o

1

0.0

G8E3E3E) CSU WT - Smooth 18.0 Deg C1=0.639

••••• CSU WT - Rough 18.1 Deg C.=O.956

.A •••• HAWT - Rough 18.5 Deg C.=O.77 ••••• HAWT - Smooth 18.5 Deg C1=0.849

0.2 0.4 0.6 0.8

Blade Chord X/C

1.0

Figure 8-11. A comparison of pressure distributions for 180 angle of attack

airfoil. On close examination, one can see that the rough wind turbine pressure data meet that flat region

about .10 xlc further toward the trailing edge than the non-rotating case. This implies that slightly delayed

separation may result from blade rotation.

Both smooth curves (open symbols) in Figure 8-9 show significantly lower (i.e., higher negative) pressures

in the low-pressure, leading edge region. Again, the rotating wind turbine blade data show a delayed

separation when compared to the wind tunnel data. The lower pressures in the leading edge region on

the smooth airfoils caused higher smooth lift coefficients. Both smooth curves resulted in CLs that were

25% higher than the rough cases (see legend in Figure 8-9 for values of Cr).

Figure 8-10 shows pressure distributions for 14-deg AOA. Here, a larger difference in leading suction

peak and separation point can be seen. The smooth curves show a Cp of -4.3 and -4.8 for the rotating

blade and the wind tunnel, respectively. Both rough cases show a maximum negative peak Cp of -3.3.

Again, the separation point was delayed about .10 xlc for the rotating blade cases over their respective

wind tunnel cases. As would be predicted from Figure 8-6, both smooth cases show higher negative

pressures over the first half of the low-pressure side ofthe airfoil. This difference is due to attached flow

extending further toward the trailing edge for the smooth cases. For the wind tunnel cases, this resulted

in a CL that was 40% greater for the smooth case than the rough case. For the rotating cases, the

difference between rough and smooth CL was only 25%.

At 18-deg AOA (Figure 8-11), the smooth wind tunnel data show a complete loss of suction peak. The

distribution of pressures on the low-pressure side of the airfoil is nearly flat from the leading edge to the

trailing edge. This is caused by complete flow separation starting at the leading edge.

70
TP-4655

On the other three curves, high, negative pressures associated with high-velocity attached flow are evident.

The rough wind tunnel data still show a strong suction peak, explaining the high CL at 18 deg in

Figure 8-6. Now, CL for the rough case is 49% higher than the smooth case. It is probable that

turbulence resulting from roughness at the leading. edge has caused energy from the outer flow to be

introduced into the inner boundary layer flow at this Reynolds number. This energy modified the

boundary layer velocity profile, making it similar to the effect of a vortex generator. The modified

velocity profile appears to have delayed flow separation and maintained the pressure peak at the leading

edge well beyond the normal stall angle.

. For the smooth rotating blade, the separation point appears to be further aft than the rough rotating case,

but no sharp transition from attached flow (decreasing pressures) to separated flow (flat pressures) is

visible in these curves. This may be an anomaly of the averaging process, or it may be caused by 3D

rotational effects. Further research is under way that is targeted at understanding the rotational and

unsteady effects of these pressure measurements and will be the subject of future reports.

Further efforts to quantify the differences in roughness sensitivity between LS(1) and the NREL airfoils

should be made using the same roughness conditions under similar conditions. It is important that a

realistic roughness distribution, appropriate for wind turbines, be used in these experiments.

71
TP-4655

9.0 References

Akins, R E., 1987, Evaluation of SERUPSC Pressure System (Unpublished), NREL, Golden, CO.

APEX Systems, Inc., 1988, PCM Decoder Card Manual, APEX Systems, Inc., Boulder, CO.

Bendat, 1. S., and Piersol, A. G., 1980, Engineering Applications of Correlation and Spectral Analysis,

A Wiley-Interscience Publication, John Wiley & Sons, New York.

Bragg, M. B., and Gregorek, G. M., 1989, "Environmentally Induced Surface Roughness Effects on

Laminar Flow Airfoils: Irilplications for Flight Safety," Proceedings ofAIAA, Aircraft Design, Systems

and Operations Conference, Seattle, WA, July 31-Aug. 2, 1989, published by AIAA, 370 L'Enfant

Promenade, S.W., Washington, D.C. 20004.

Butterfield, C. P., Scott, G. N., and Musial, W., 1990, Comparison of Wind Tunnel Airfoil Performance

Data with Wind Turbine Blade Data, 'IP-254-3799, NREL, Golden, CO.

Butterfield, C. P., 1989b, Three-Dimensional Airfoil Performance Measurements on a Rotating Wing,

'IP-217-3505, NREL, Golden, CO.

Butterfield, C. P., Jenks, M. D., Simms, D. A., and Musial, W. P., 1990, Aerodynamic Pressure

Measurements on a Rotating Wind Turbine Blade, 'IP-257-3695, NREL, Golden, CO.

Butterfield, C. P., 1989a, "Aerodynamic Pressure and Flow Visualization Measurements from a Rotating

Wind Turbine Blade," Proceedings of the Eighth ASME Wind Energy Symposium, Houston, TX,

January 22-25, 1989, Vol. 7, pp. 245-255.

Butterfield, C. P., and Nelson, E. N., 1990, Aerodynamic Testing of a Rotating Wind Turbine Blade,

'IP-257-3490, NREL, Golden, CO.

Fairchild Weston Systems, Inc., 1985, PCM Data Collection and Reduction System for the Solar Energy

Research Institute: Operating Manual, Fairchild Weston Systems, Inc., Sarasota, FL.

Gregorek, G. M., Hoffman, M. J., and Mulh, K.. E., 1991, Wind Tunnel Tests of the S809 Airfoil Model,

NREL, Golden, CO.

Hoerner, S. F., 1975, Fluid-Dynamic lift. Hoerner Fluid Dynamics, Brick Town, NJ.

Holtz, R., 1988, "The Effect of Blade Surface Roughness on the Lead-Lag Bending Moments of a U.S.

Windpower 56-100 Wind Turbine," Proceedings of the Seventh ASME Wind Energy Symposium,

American Society of Mechanical Engineers, New Orleans, Louisiana, Jan. 10-13, 1988, pp. 95-99.

Irwin, H., Cooper, K. R, and Hirard, R, 1979, "Correction of Distortion Effects Caused by Tubing

Systems in Measurements of Fluctuating Pressures," Journal ofIndustrial Aerodynamics 5, pp. 93-107.

Lenschow, D. H., 1971, "Vanes for Sensing Incidence Angles of the Air from an Aircraft," Journal of

Applied Meteorology, Vol. 10, No.6, pp. 1339-1343. .

72
TP-4655

Lora! Instrumentation, DIPAD Mark II Manual, Loral Instrumentation, San Diego, CA.

Madsen, H. A., Rasmussen, F., and Pedersen, T. F., 1988, Aerodynamics ofa Full-Scale HAWT Blade,

Riso National Laboratory, Roskilde, Denmark.

McGhee, R. J., Beasley, W. D., and Somers, D. M., 1977, Low-Speed Aerodynamic Characteristics of a

13-Percent-Thick Airfoil Section Designed for General Aviation Applications, NASA TM X-72697,

Langley Research Center, Hampton, VA.

McGhee, R. J., and Beasley, W. D., 1981, Wind Tunnel Results for a Modified 17-Percent Thick LowSpeed Airfoil Section, Technical Paper 1919, National Aeronautics and Space Administration, Houston,

TX.

Miley S. J., 1982, A Catalog ofLow Reynolds Number Airfoil Data for Wind Turbine Applications, RFP3387, U.S. Department of Energy, Washington, D.C.

Musial, W. D., Butterfield C. P., and Jenks, MD., 1989, Effects ofLeading-edge Roughness on S809

Airfoil Rotor Performance, TP-217-3563, NREL, Golden, CO.

Musial, W., and Butterfield, C. P., 1990, A Comparison ofTwo- and Three- Dimensional S809 Airfoil

Properties for Rough and Smooth HAWT Rotor Operation, TP-257-3603, NREL, Golden, CO.

Rae, H. W., and Pope, A., 1984, Low-Speed Wind Tunnel Testing, Second Edition, John Wiley & Sons,

New York.

Rae, W. H., Jr., and Pope, A., 1984, Low-Speed Wind Tunnel Testing, Second Edition, John Wiley &

Sons, New York, p. 133.

Simms, D. A., and Butterfield, C. P., 1990, Unsteady Aero Experiment "[est Plan (Unpublished), NREL,

Golden, CO.

Simms, D. A., 1990, PC-Based PCM Telemetry Data Reduction System Software, '):P-257-3663, NREL,

Golden, CO.

Simms, D. A., and Butterfield, C. P., 1990, PC-Based PCM Telemetry Data Reduction System Hardware,

TP-257-3662, NREL, Golden, CO.

Somers, D. M, 1989, Design and Experimental Results for the S809 .Airfoil (Unpublished), NREL,

Golden, CO.

Somers, D. M., 1991, Design and Experimental Results for the S809 Airfoil, NREL report, to be

published

Strock, O. J., 1983, Telemetry Computer Systems: An Introduction, Prentice-Hall, Inc., Englewood Cliffs,

NJ. -

Tangler, J. L., 1983, Horizontal-Axis Wind System Rotor Performance Model Comparison - A

Compendium, RFP-3508, Rockwell International.

73
TP-4655

Vitema, L. A., and Corrigan, R. D., 1981, "Fixed Pitch Rotor Performance ofLarge Horizontal Axis Wind

Turbines," DOEJNASA Workshop on Large Horizontal Axis Wind Turbines, Cleveland, OH, July 28-

30. .

Yekutieli, 0., and Clark, R. N., 1987, "Influence ofBlade Surface Roughness on the Performance ofWind

Turbines," Proceedings ofthe Sixth ASME Wind Energy Symposium, pp. 181-187, American Society

of Mechanical Engineers, Dallas TX, Feb. 15-18, 1987.

74
Appendix A

Combined/Unsteady Aero Experiment

High and Low Cal Setups for PCM600

A-I
Combined/Unsteady Aero Experiment

Hig~ and Low Cal Setups for PCM600

Data Stream #1

Low Cal High Cal

PCM Input Input Output Input Output

Ch # Description Range Voltage Counts Voltage Counts Gain Offset Filter

1 20m Hot Film (Not Used) 0-10 V OV SO +10 V 4049 1 -S V 10 Hz

2 18m Sonic A (Not Used) +/-S V OV 20S0 +S V 4049 1 OV 10 Hz

3 18m Sonic B (Not Used) +/-S V OV 20S0 +S V 4049 1 OV 10 Hz

4 18m Sonic C (Not Used) +/-S V OV 20S0 +S V 4049 1 OV 10 Hz

S SmWD O-SV OV SO +S V 4049 2 -S V 1 Hz

6 SmWS O-S V OV SO +S V 4049 2 -S V 1 Hz

7 10mWD O-S V OV SO +S V 4049 2 -S V 1 Hz

8 10mWS O-SV OV SO +S V 4049 2 -S V 1 Hz

9 20mWD O-S V OV SO +S V 4049 2 -S V 1 Hz

10 20mWS O-SV OV SO +S V 4049 2 -S V 1 Hz

11 SOmWD O-S V OV SO +S V 4049 2 -S V 1 Hz

12 SOmWS O-SV OV SO +S V 4049 2 -S V 1 Hz

13 Sm Air Tempereture 0-5 V OV SO +S V 4049 2 -S V 1 Hz

14 Delta Temp(TSO-TS) O-S V OV SO +S V 4049 2 -S V 1 Hz

lS Sm Dew Point (Not Used) +/-S V OV 20S0 +SV 4049 1 OV 1 Hz

16 Baro Pressure O-S V OV SO +S V 4049 2 -S V 1 Hz

Note: All voltages are RDCRunless otherwise stated.

Bit Rate = 7.Sk bits/second (1.92MHz/2S6)

Sample Rate = 34.72 samples/second

BitslWord = 12

Words/Frame = 18 (16 data channels + 2 frame sync)

Frame Sync Code =000 110 101110 010 100011 010

A-2
Combined/Unsteady Aero -Experiment

High and low Cal Setups for PCM600

Data Stream #2

Low C.I High C.I

PCM Input Input Output Input Output

Ch # Description Range Voltage Counts Voltase Counts Gain Offset Filter

1 Propvane Anem. WS1 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

2 Propvane Anem. WS2 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

3 Propvane Anem. WS3 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

4 Propvene Anem. WS4 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

5 Propvane Anem. WS5 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

6 Propvane Anem. WS6 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

7 Propvane Anem. WS7 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

8 Propvene Anem •.WS8 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

9 Propvane Anem. WS9 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

10 Propvane Anem. W09 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

11 Bivane WS12 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

12 Bivane WD12 0-2 V OV 50 +2.5V 4049 4 -5 V 2 Hz

13 Bivane WE12 0-2 V OV 50 +2.5V 4049 4 -5 V 2 Hz

14 Bivane WS13 0-10 V OV 50 +10 V 4049 1 -5 V 2 Hz

15 Bivane WD13 0-2 V OV 50 +2.5V 4049 4 -5 V 2 Hz

16 Bivane WE13 0-2 V OV 50 +2.5 V 4049 4 -5 V 2 Hz

Note: All voltages are "DC" u,nless otherwise stated.

Bit Rate ZI 15k bits/second (1.92MHz/128)

Sample Rate = 69.44 samples/second

BitslWord = 12

Words/Frame = 18 (16 data channels + 2 frame sync)

Frame Sync Code =000 110 101 110 010 100011 010

A-3
Combined/Unsteady Aero Experiment

High and Low Cal Setups for PCM600

Data Stream #3 '

Low Cal High Cal

PCM Input Input Output Input Output

Ch # Description Range Voltage Counts Voltase Counts Gain Offset Filter

1 Propvane Anem. WS10 0-10V OV 50 +10 V 4049 1 -5 V 2 Hz

2 Propvane Anem. WS11 Q.l0 V OV 50 +10 V 4049 1 -5 V 2 Hz

3 LSS Azimuth 0-5 V OV 50 +5V 4049 2 -5 V· 130 Hz

4 Yaw Bending +/- 24.75 mV -24.75 mV 50 +24.75 mV 4049 202 OV 40 Hz

5 Tower Bending N-S +/- 5.05 mV -5.05 mV 50 +5.05 mV 4049 990 OV 40 Hz

6 Towar Bending E-W +5.03/-5 mV -5 mV '50 +5.03 mV 4049 997 OV 40 Hz

7 Yaw Angle 0-10 V OV 50 +10 V 4049 1 -5 V 10 Hz

8 Generator Power +/- 5 V OV 2050 +5 V 4049 1 OV 55 Hz

9 LSS Speed (Not Used) 0-10 V OV 50 +8 V 3277 1 -5 V 10 Hz

10 TSI X-Film 1X (Not Used) 2.1-5.7 V 3.9 V 2048 +5.0 V 3277 2.778 -10.8 V 55 Hz

11 TSI X-Film 1Y (Not Used) 2.1-5.7 V 3.9 V 2048 +5.0V 3277 2.778 -10.8 V ·55 Hz

12 TSI X-Film 2X (Not Used) 2.1-5.7 V 3.9 V 2048 +5.0 V 3277 2.778 -10.8 V 55 Hz

13 TSI X-Film 2Y (Not Used) 2.1-5.7 V 3.9 V 2048 +5.0 V 3277 2.778 -10.8 V 55 Hz

14 Sonic U-Axis (Not Used) +/- 5 V OV 2048 +3 V 3277 1 OV 12 Hz

15 Sonic V-Axis (Not Used) +/- 5 V OV 2048 +3 V 3277 1 OV 12 Hz

16 Sonic W-Axis (Not Used) +/- 5 V OV 2048 +3 V 3277 1 OV 12 Hz

Note: All voltages are wDC· unless otherwise stated.

There ere onlv 8 of 16 channels installed in this PCM Stream (3) the signal conditioners are removed until there is a need for

channels 9-16.

Bit Rate

Sample Rate

BitslWord

Words/Frame

Frame Sync Code

:: 60k bits/second (1.92MHz/321

:: 277.78 samples/second

:: 12

= 18 (16 data channels + 2 frame sync)

= 000 110 101 110 010 100011 010

A-4
Combined/Unsteady Aero Experiment

High and Low Cal Setups for PCM600

Data Stream #4

Low C.I High C.I

PCM Input Input Output Input Output

Ch # Description Range Voltage Counts Voltage Counts Gain Offset Filter

1 Root Flap "RTFBM-A" ±6.25 mV OV 2048 800 OV 40 Hz

2 Root Flap "RTFBM-B" ±5.0 mV OV 2048 1000 OV 40 Hz

3 Root FI Blade 2 "RTFBM-2" ±5.0 mV OV 2048 1000 OV 40 Hz

4 Root Fl Blade 3 "RTFBM-3" ±6.25 mV OV 2048 800 OV 40 Hz

5 20% Flap "20FBM" ±5.0 mV OV 2048 1000 OV 40 Hz

6 40% Flap"4OFBM" ±10.0mV OV 2048 500 OV 40 Hz

7 50% Flap "50FBM" ±7.0 mV OV 2048 700 OV 40 Hz

8 60% Flap "60FBM" (Not Used) •

9 70% Flap "70FBM" ±S.O mV OV 2048 1000 OV 40 Hz

10 75% Flap "75FBM"(Not Used) -

11 80% Flap "80FBM" (Not Used) -

12 85% Flap "85FBM" (Not Used) -

13 90% Flap "90FBM" ±2.5 mV OV 2048 2000 OV 40 Hz

14 Root Edge "RTEBM-A" ±6.2S mV OV 2048 800 OV 40 Hz

15 20% Edge"20EBM" ·± 7.0 mV OV 2048 700 OV 40 Hz

16 50% Edge"50EBM" ±10.0 mV OV 2048 500 OV 40 Hz

17 70% Blade Torque "70Ta" ± 2.5 mV OV 2048 2000 OV 40 Hz

18 85% Edge "85EBM" (Not Used)-

19 Root Torque (Unk) "RTTa" ± 2.5 mV OV 2048 2000 OV 40 Hz

20 50% Torsion "SOTa" ±2.5 mV OV 2048 2000 OV 100 Hz

21 X-X LSS "LSSX-X" ± 10.0 mV OV 2048 500 OV 40 Hz

22 V-V LSS "LSSY-Y" ± 10.0 mV OV 2048 500 OV 40 Hz

23 LSS Torque "LSSTa-A" ±5.0 mV OV 2048 1000 OV 40 Hz

24 LSS Torque "LSSTa-B" ±5.0 mV OV 2048 1000 OV 100 Hz

25 85% RTD (Not Used)

26 Load Cell for Blade Pull Testing (Cal Only)

'27-58 Pressure Taps ±S.OV 1 OV 100 Hz

59 Absolute Pressure 0-5 V 2 :'5 V 1.5 kHz

60 Ca' Pressure ±2.5 V 2 OV 1.5 kHz

61 Pitch ·Angle 0-5 V 1 OV

62 PCM Voltage Monitor 0-28 V .2 OV

Note: All voltages are "DC" unless otherwise stated.

Bit Rate ::II: 400k bits/second

Sample Rate = 520.83 samples/second

BitslWord = 12

Words/Frame - 64 (62 data channels + 2 frame sync)

Frame Sync Code - 111110101 111 001 100 100000

A-5
Combined/Unsteady Aero Experiment

High and Low Cal Setups for PCM600

Data Stream #8

PCM

Ch#

1

2

3

4-62

Description

Absolute Pressure

Cal Pressure

Spare

Pressure Taps

Input

Range

0-5 V

±2.5 V

±5.0 V

Low Cal

Input Output

Voltage Counts

Data Stream #9

High Cal

Input Output

Voltage Counts Gain Offset Filter

2 -5 V 1.5 kHz

2 0 V 1.5 kHz

o V 100 Hz

PCM

Ch#

1·34

35

36

37

38

39

40

41

42-45

46

47-52

53

54

55-62

Description

Pressure Taps

86% AOA

Spare

67.3% AOA

Spare

Spare

Spare

34% AOA

Spare

50.6% AOA

Spare

Absolute Pressure

Cal Pressure

Spare

Input

Range

±5.0 V

± 10.0 V

± 10.0 V

±10.0 V

± 10.0 V

0-5 V

±2.5 V

Low Cal

Input Output

Voltage Counts

High Cal

Input Output

Voltage Counts Gain

1

2

2

Offset Filter

o V 100 Hz

OV

OV

OV

OV

-5 V 1.5 kHz

o V 1.5 kHz

Note: All voltages are "DC" unless otherwise stated.

Bit Rate

Sample Rate

BitslWord

Words/Frame

Frame Sync Code

= 400k bits/second

= 520.83 samples/second

= 12

= 64 162 data channels + 2 frame sync)

= 111110101111 001100100000

A-6
Appendix B

Unsteady Aero Experiment Measurement Tolerances

B-1
Unsteady Aero Experiment Measurement Tolerances *

Quick Cal Measurement Range Allowable Accuracy Max std

Look Description Procedure Max Calibrated Error Req'd error

Number # (EU) (EU) (%) (±EU) (EU)

PCM1: North Met Tower (7.5 Kb/s, 34.72 Hz, 28.8 ms):

101 20 M Hot Film (Not Used)

102 18 M Sonic Channel A (Not Used)

103 18 M Sonic Channel B (Not Used)

104 18 M Sonic Channel C (Not Used)

105 5 M Wind Direction (Not Used)

106 5 M Wind Speed (m/s) M1,E1 Oto90 oto 25 1.1 .5 .25

107 10 M Wind Direction (Not Used)

108 10 M Wind Speed (m/s) M1,El Oto 90 Oto 25 1.1 .5 .25

109 20 M Wind Direction (Not Used)

110 20 M Wind Speed (m/s) Ml,El Oto90 oto 25 1.1 .5 .25

111 50 M Wind Direction (Not Used)

112 50 M Wind Speed (m/s) ·Ml,E1 oto 90 oto 25 1.1 .5 .25

113 5 M Air Temperature (C) Ml,ES ±50 ±50 2.0 1.0 .5

114 Delta Temperature (C) Ml,E4 -4.4 to 6.7 -4.4 to 3.3 1.8 .1 .05

115 5 M DP (Not Used)

116 Baro Pressure (mb) M1,E3 700 to 930 711 to 914 1.7 2.0 1.5

PCM2: Vertical Plane Array (15.0 Kb/s, 69.44 Hz, 14.4 ms):

201 VPA Prop Vane WS-1 (m/s) Al,El oto 37 Oto25 2.7 .5 .25

202 VPA Prop Vane WS-2 (m/s) Al,El Oto 37 oto 25 2.7 .5 .25

203 VPA Prop Vane WS-3 (m/s) Al,El oto 37 oto 25 2.7 .5 .25

204 VPA Prop Vane WS-4 (m/s) Al,E1 oto 37 Oto 25 2.7 .5 .25

205 VPA Prop Vane WS-5 (m/s) Al,E1 oto 37 oto 25 2.7 .5 .25

206 VPA Prop Vane WS-6 (m/s) Al,E1 oto 37 Oto 25 2.7 .5 .25

207 VPA Prop Vane WS-7 (m/s) Al,El Oto 37 oto 25 2.7 .5 .25

208 VPA Prop Vane WS-8 (m/s) A1,E1 Oto 37 oto 25 2.7 .5 .25

209 VPA PV Hub Height WS-9 (m/s) Al,El oto 37 01025 2.7 .5 .25

210 VPA PV Hub Height WD-9 (deg) Al,M6 0 to 360 112 to 292 .56 (f) 2.0 1.0

211 VPA Bi-Vane WS-12 (m/s) A1,E1 oto 37 oto 25 2.7 .s .25

212 VPA Bi-Vane WD-12 (deg) A1,M6 0 to 360 112 to 292 .56 (f) 2.0 1.0

213 VPA Bi-Vane Wa-12 (deg) A1,M7 ±50 ±20 2.0 .5 .25

214 VPA Bi-Vane WS-13 (m/s) A1,E1 oto 37 oto 25 2.7 .s .25

215 VPA Bi-Vane WD-13 (deg) A1,M6 0 to 360 112 to 292 .56 (f) 2.0 1.0

216 VPA Bi-Vane Wa-13 (deg) A1,M7 ±50 ±20 2.0 .5 .25

PCM3: VPA, Local Met, Tower, Turbine (60.0 Kb/s, 277.78 Hz, 3.6 ms):

301 VPA Prop Vane WS-lO (m/s) A1,E1 oto 37 oto 25 2.7 .5 .25

302 VPA Prop Vane WS-11 (m/s) A1,E1 oto 37 oto 25 2.7 .5 .25

303 LSS Azimuth Angle (deg) A1,M5 0 to 360 90 to 270 .28 (f) 1.0 .5

304 Yaw Moment (NT-m) A1,M10 ±3500 5.0 175 88

305 Tower Bending E-W (NT-m) A1,M9 ±55000 ±5200 5.0 2750 1375

306 Tower Bending N-S (NT-m) A1,M9 ±55000 ±5200 5.0 2750 1375

)07 Yaw Angle (deg) A1,M4 0 to 360 112 to 292 .56 (f) 2.0 1.0

308 Generator Power (Kw) A1,E6 ±40 ±80 1.25 .5 .25

309 LSS Speed (Not Used)

310 TSI (South) X-Film U (Not Used)

311 TSI (South) X-Film W (Not Used)

312 TSI (North) X-Film U (Not Used)

313 TSI (North) X-Film W (Not Used)

314 Sonic Anemometer Ch A (Not Used)

315 Sonic Anemometer Ch B (Not Used)

316 Sonic Anemometer Ch C (Not Used)

B-2
Unsteady Aero Experiment Measurement Tolerances* (continued)

Quick Cal Measurement Range Allowable Accuracy Max std

Look Description Procedure Max Calibrated Error Req'd error

Number # (EU) (EU) (%) (±EU) (EU)

PCM4: Rotating Strain Gages, 80% Pressures (400.0 Kb/s, 520.83 Hz, 1.92 IDS):'

401 Root Flap Bending WRTFBM-AW(NT-m) A2,MS ±3200 oto IS00 5.0 160 80

402 Root Flap Bending wRTFBM-Bw (NT-m) A2,MS ±3200 O.to IS00 5.0 160 80

403 Root Flap Blade 2 wRTFBM-2w(NT-m) A2,MS ±3200 oto IS00 5.0 160 SO

404 Root Flap Blade 3 wRTFBM-3w(NT-m) A2,MS ±3200 oto.lS00 5.0 160 SO

405 20 % Flap Bending w20FBMw(NT-m) A2,MS ±3000 oto 1555 5.0 150 . 75

406 40%Flap Bending -4OFBM- (NT-m) A2,M8 ±2300 oto 1150 5.0 115 58

407 50% Flap Bending "SOFBM" (NT-m) A2,MS ±1400 oto 950 5.0 70 35

40S 60% Flap Bending w60FBMw (Not Used)

409 70% Flap Bending "70FBMw(NT-m) A2,MS ±SOO oto 550 5.0 40 20

410 75 % Flap Bending "75FBMw (Not Used)

411 SO% Flap Bending "SOFBMw(Not Used)

412 S5% Flap Bending "85FBMw(Not Used)

413 90% Flap Bending w90FBMw(NT-m) . A2,MS ±300 oto 145 5.0 15 S

414 Root Edge Bending "RTEBM-A W(NT-m) A2,MS ±3200 oto 1800 5.0 160 80

415 20 % Edge Bending w20EBMw(NT-m) A2,MS ±3000 oto 1555 5.0 150 75

416 50% Edge Bending "50EBMw(NT-m) A2,MS ±1400 oto ·950 5.0 70 35

417 70% Blade Torque "70TQ" (NT-m) A2,MS ±1100 oto 550 5.0 55 2S

418 S5'% Edge Bending wS5EBM" (Not Used)

419 Root Torque (Link) wRTTQw (NT-m) A2,MS ±205 oto 4S0 5.0 10 5

420 50% Torsion w50TQ" (NT-m) A2,M8 ±300 oto 480 5.0 15 8

421 X-X LSS Bending "LSSX-X" (NT-m) A2,MS ±13000 5.0 650 325

422 y-y LSS Bending WLSSY-Y" (NT-m) A2,MS ±13000 5.0 650 325

423 LSS Torque "LSSTQ-A" (NT-m) A2,MS ±6500 oto 2000 5.0 325 163

424 LSS Torque "LSSTQ-B" (NT-m) A2,MS ±6500 oto 2000 5.0 325 163

425 85 % RTD (Not Used)

426 Load Cell for Blade Pull Testing (NT) A2,M8 0-900 oto 900 2.0 (f) 18 9

427 Pressure #1 StaPTIO, 100% trailing (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

428 Pressure #2 StaPTIO, 92% upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

429 Pressure #4 StaPTIO, SO% upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

430 Pressure #6 StaPTI0, 68 % upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

431 Pressure #S StaPTI0, 56% upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 . .00347

432 Pressure #10 StaPTI0, 44% upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

433 Pressure #11 StaPTI0, 36% upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

434 Pressure #12 StaPTIO, 2S % upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

435 Pressure #13 StaPTI0, 20% upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

. 436 Pressure #14 StaPTI0, 14% upper (psi) A3,A4 ±1.2 ±O.3 .579 .00695 .00347

437 Pressure #15 StaPTI0, 10% upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

43S Pressure #16 StaPTI0, 8% upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

439 Pressure #17 StaPTIO, 6% upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

440 Pressure #IS StaPTI0, 4% upper (psi) A3,A4 ±1.2 ±O.3 .579 .00695 .00347

441 Pressure #19 StaPTI0, 2 % upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

442 Pressure #20 StaPTI0, 1.% upper (psi) A3,A4 ±1.2 ±0.3 ·.579 .00695 .00347

443 Pressure #21 StaPTI0, 0.5 % upper (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

444 Pressure #22 StaPTI0, 0% leading (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

445 Pressure m StaPTI0, 0.5 % lower (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

446 Pressure #24 StaPTI0, 1% lower (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

447 Pressure #25 StaPTI0, 2% lower (psi) A3,A4 ±1.2 ±O.3 .579 .00695 .00347

448 Pressure #26 StaPTI0, 4% lower (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

449 Pressure #28 StaPTI0, S% lower (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

450 Pressure #30 StaPTI0, 14% lower (psi) A3,A4 ±1.2 ±O.3 .579 .00695 .00347

451 Pressure #32 StaPTI0, 2S% lower (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

452 Pressure #34 StaPTI0, 44% lower (psi) A3,A4 ±1.2 ±O.3 .579 .00695 .00347

B-3
Unsteady Aero Experiment Measurement Tolerances" (continued)

Quick Cal Measurement Range Allowable Accuracy Max std

Look Description Procedure Max Calibrated Error Req'd error

Number # (BU) (BU) (%) (±EU) (BU)

PCM4: Continued (400.0 Kb/s, 520.83 Hz, 1.92 ms)

453 Pressure #36 StaPT10, 68 % lower (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

454 Pressure #38 StaPT10, 92 % lower (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

455 Pressure #1~ StaPT9, 4% upper (psi) A3,A4 ±1.2 ±0.3 .500 .00600 .00300

456 Pressure #11 StaPT9, 36% upper (psi) A3,A4 ±1.2 ±0.3 .500 .00600 .00300

457 Pressure #11 StaPT8,36% upper (psi) A3,A4 ±1.2 ±0.3 .439 .00527 .00264

458 Total Pressure Probe, 86 % span (psi) A3,A4 ±1.2 ±0.3 .579 .00695 .00347

459 Absolute Reference Pressure (mb) E3 800-1100 711-914 2.0 3.0 1.5

460 Calibration Pressure (psi) (Cal Only) E2 ±0.3 ±0.5 .222 (f) .00133 .00044**

461 Pitch Angle (degrees) M3 -106 to 71 -10 to 20 1.0 1.0 .5

462 PCM Voltage Monitor (Quick-Look Only) ±140 10 14 7

PCM8: Rotating 30% and 40% Pressures (400.0 Kb/s, 520.83 Hz, 1.92 ms):

801 Absolute Reference Pressure (Not Used)

802 Calibration Pressure (Cal Only) E2 ±0.3 ±0.5 .222 (f) .00133 .00044**

803 Spare

804 Pressure #1 StaPT1, 100% trailing (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

805 Pressure #4 StaPT1, 80% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

806 Pressure #6 StaPT1, 68% upper (Psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

807 Pressure #8 StaPT1, 56 % upper (Psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

808 Pressure #10 StaPT1, 44% upper (psi) A2,A3 ±0.43 ·± 0.3 .310 .00133 .00067

809 Pressure #11 StaPT1, 36% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

810 Pressure #13 StaPT1, 20% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

811 Pressure #14 StaPT1, 14% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

812 Pressure #15 StaPT1, 10% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

813 Pressure #16 StaPT1, 8% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

814 Pressure #17 StaPT1, 6% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

815 Pressure #18 StaPTl, 4% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

816 Pressure #19 StaPT1, 2% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

817 Pressure #21 StaPTl, 0.5% upper (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

818 Pressure #22 StaPTl, 0% leading (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

819 Pressure #23 StaPT1, 0.5% lower (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

820 Pressure #24 StaPT1, 1% lower (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

821 Pressure #2S StaPT1, 2 % lower (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

822 Pressure #26 StaPT1, 4% lower (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

823 Pressure #28 StaPTl, 8% lower (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

824 Pressure #30 StaPT1, 14% lower (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

825 Pressure #31 StaPTl, 20% lower (psi) A2,A3 ±0.43 ±0.3 .•310 .00133 .00067

826 Pressure #34 StaPT1, 44% lower (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

827 Pressure #36 StaPT1, 68 % lower (Psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

828 Pressure #38 StaPT1, 92%' lower (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

829 Pressure #18 StaPT2, 4% upper (psi) A2,A3 ±0.43 ±0.3 .404 .00174 .00087

830 Pressure #11 StaPT2, 36 % upper (psi) A2,A3 ±0.43 ±0.3 .404 .00174 .00087

831 Pressure #11 StaPT3, 36% upper (psi) A2',A3 ±0.43 ±0.3 .495 .00213 .00106

832 Total Pressure Probe, 34 % span (psi) A2,A3 ±0.43 ±0.3 .310 .00133 .00067

833 Pressure #1 StaPT4, 100% trailing (psi) A2,A3 ±0.43 ±0.3 .620 .00267 .00133

834 Pressure #2 StaPT4, 92% upper (psi) A2,A3 ±0.43 ±0.3 .620 - .00267 .00133

835 Pressure #4 StaPT4, 80% upper (psi) A2,A3 ±0.43 ±0.3 .620 .00267 .00133

836 Pressure #6 StaPT4, 68% upper (psi) A2,A3 ±0.43 ±0.3 .620 .00267 .00133

837 Pressure #8 StaPT4, 56 % upper (psi) A2,A3 ±0.43 ±0.3 .620 .00267 .00133

838 Pressure #10 StaPT4, 44% upper (psi) A2,A3 ±0.43 ±0.3 .620 .00267 .00133

839 Pressure #11 StaPT4, 36 % upper (psi) A2,A3 ±0.43 ±0.3 .620 .00267 .00133

840 Pressure #12 StaPT4, 28 % upper (psi) A2,A3 ±0.43 ±0.3 .620 .00267 .00133

B-4
Unsteady Aero Experiment Measurement Tolerances* (continued)

Quick Cal Measurement Range Allowable Accuracy Max std

Look Description Procedure Max Calibrated Error Req'd " error

Number # (EU) (ED) (%) (±EU) (EU)

PCM8: Continued (400.0 Kb/s, 520.83 Hz, 1.92 ms):

841 Pressure #13 StaPT4, 20% upper (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

842 Pressure #14 StaPT4, 14% upper (Psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

843 Pressure #15 StaPT4, 10% upper (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

844 Pressure #16 StaPT4, 8 % upper (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

845 Pressure #17 StaPT4, 6 % upper (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

846 Pressure #18 StaPT4, 4% upper (psi) A2,AJ ±0.43 . ±0.3 .620 .00267 .00133

847 P~#19 StaPT4, 2 % upper (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

848 Pressure #20 StaPT4, 1% upper (Psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

849 Pressure #21 StaPT4, 0.5 % upper (psi) ~,AJ ±0.43 ±0.3 .620 .00267 .00133

850 Pressure #22 StaPT4, 0% leading (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

851 Pressure #23 StaPT4, 0.5 % lower'(psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

852 Pressure #2S StaPT4, 2% lower (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

853 Pressure #26 StaPT4, 4% lower (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

854 Pressure #27 StaPT4, 6% lower (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

855 Pressure #28 StaPT4, 8% lower (psi) - A2,AJ ±0.43 ±0.3 .620 .00267 .00133

856 Pressure #30 StaPT4, 14% lower (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

857 Pressure #32 StaPT4, 28% lower (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

858 Pressure #34 StaPT4, 44 % lower (psi) A2,A3 ±0.43 ±0.3 .620 .00267 .00133

859 Pressure #36 StaPT4, 68 % lower (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

860 Pressure #38 StaPT4, 92 % lower (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

861 Pressure #18 StaPT3, 4% upper (psi) A2,AJ ±0.43 ±0.3 .495 .00213 .00106

862 Total Pressure Probe, 50.6 % span (psi) A2,AJ ±0.43 ±0.3 .620 .00267 .00133

PCM9: Rotating 63% Pressures, Angle of Attack (400.0 Kb/s, 520.83 Hz, 1.92 ms):

901 Pressure #11 StaPTS, 36 % upper (psi) A2,AJ ±1.2 ±0.3 .262 .00317 .00159

902 Pressure #18 StaPT5, 4% upper (psi) A2,AJ ±1.2 ±0.3 .262 .00317 .00159

903 Pressure #1 StaPT7, 100% trailing (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

904 Pressure #2 StaPT7, 92 % upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

905 Pressure #4 StaPT7, 80 % upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

906 Pressure #6 StaPT7, 68 % upper (psi) A2,A3 ±1.2 ±0.3 .372 .00447 .00223

907 Pressure #8 StaPT7, 56 % upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

908 Pressure #10 StaPT7, 44% upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

909 Pressure #11 StaPT7, 36 %upper (psi) A2,A3 ±1.2 ±0.3 .372 .00447 .00223

910 Pressure #12 StaPT7, 28 % upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

911 Pressure #13 StaPT7, 20 % upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

912 Pressure #14 StaPT7, 14% upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

913 Pressure #15 StaPT7, 10 % upper (psi) A2,A3 ±1.2 ±0.3 .372 .00447 .00223

914 Pressure #16 StaPT7, 8 % upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

915 Pressure #17 StaPT7, 6% upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

916 Pressure #18 StaPT7, 4% upper (psi) A2,A3 ±1.2 ±0.3 .372 .00447 .00223

917 Pressure #19 StaPT7, 2 % upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

918 Pressure #20 StaPT7, 1% upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

919 Pressure #21 StaPT7, 0.5 % upper (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

920 Pressure #22 StaPT7, 0% leading (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

921 Pressure #23 StaPT7, 0.5% lower (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

922 Pressure #24 StaPT7, 1% lower (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

923 Pressure #2S StaPT7, 2 % lower (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

924 Pressure #26 StaPT7, 4 % lower (psi) A2,A3 ±1.2 ±0.3 .372 .00447 .00223

925 Pressure #28 StaPT7, 8 % lower (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

926 Pressure #30 StaPT7, 14% lower (psi) A2,AJ ±1.2 ±O.3 .372 .00447 .00223

927 Pressure #32 StaPT7, 28 % lower (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223 .

928 Pressure #34 StaPT7, 44 % lower (psi) A2,AJ ±1.2 ±0.3 .372 .00447 .00223

B-5
Unsteady Aero Experiment Measurement Tolerances* (continued)

Quick Cal Measurement Range Allowable Accuracy Max std

Look Description Procedure Max Calibrated Error Req'd error

Number # (EU) (EU) (%) (±EU) (EU)

PCM9: Continued (400.0 Kb/s, 520.83 Hz, 1.92 ms):

929 Pressure #36 StaPTI, 6~ % lower (Psi) A2,A3 ±1.2 ±0.3 .372 .00447 .00223

930 Pressure #38 StaPTI; 92% lower (psi) A2,A3 ±1.2 ±0.3 .372 .00447 .00223

931 Pressure #18 StaPT6, 4% upper (psi) . A2,A3 ±1.2 ±0.3 .321 .00386 .00192

932 Pressure #18 StaPT8, 4% upper (psi) A2,A3 ±1.2 :to.3 .439 .00527 .00264

933 Pressure #11 StaPT6, 36 % upper (Psi) A2,A3 ±1.2 ±0.3 .321 .00386 .00192

934 Total Pressure Probe, 67.3 % span (psi) A2,A3 ±1.2 ±0.3 .372 .00447 .00223

935 Angle-of-Attack, 86% span (degrees) M2 -22 to 55 -20 to 40 2.6 1.0 .5

936 Ground

937 Angle-of-Attack, 67.3 % span (degrees) M2 -22 to 55 -20 to 40 2.6 1.0 .5

938 Ground

939 Do Not Use (Bad channel)

940 Ground

941 Angle-of-Attack, 34% span (degrees) M2 -22 to 55 -20 to 40 2.6 1.0 .5

942 Ground

943 Nitrogen Pressure (psi) (Quick-Look Only) ±2000 10 200 100

944 +15 Volt Power Monitor (V) (Quick-Look Only)- ±20 10 1.5 .8

945 -15 Volt Power Monitor (V) (Quick-Look Only) - ±20 10 1.5 .8

946 Angle-of-Attack, 50.6 % span (degrees) M2 -22 to 55 -20 to 40 2.6 1.0 .5

947 DC Ground Monitor (counts) (Quick-Look Only) - oto 4095

948 Spare

949 Spare

950 Spare

951 Spare

952 Spare

953 Absolute Reference Pressure E3 800-1100 711-914 2.0 3.0 1.5

954 Calibration Pressure (Cal Only) E4 ±0.3 ±0.5 .222 (f) .00133 .00044**

955 Spare

956 Spare

957 Spare

958 Spare

959 Spare

960 Spare

961 Spare

962 Spare

Notes

* All measured channels and their corresponding calibration requirements are listed here. The first column

shows channel ID number as it is referenced by the Quick-Look system. The first digit is the PCM stream

number and the next two digits are the PCM frame number. Column 2 contains channel descriptions and units.

Each channel has defined calibration procedures identified in column 3 which are performed to measure the end to

end accuracy of all channels. The procedures are identified by the letter A, E or M, followed by a number. The

letter designates 3 basic types of calibrations An WEWdesignates those channels in which the transducer requires

an external calibration, such as anamometers in the wind tunnel. An WAWdesignates an automatic calibration in

which many incoming signals can be automatically placed in a known calibration state. An wMw designates

calibrations which require manual placement of transducers into a position to enable calibrating. The number

which follows identifies a specific procedure to be followed in order to calibrate that channel. These are

described in detail in Appendix D. Channels with type wEwcalibrations are done in two parts in which the

transducer and electronics are calibrated separately, then RMS summed to determine overall channel accuracy.

All other channels are end-to-end calibrated to directly measure the full channel response. Some channels (such as

pressures and strain-gages) require two end-to-end cals, one to calculate slope, and another to calculate offset.

B-6
The next two columns show the measurement range. Column 4 shows the full data range by identifying estimated

data extremes over which accurate measurements can be made. Column 5 shows the range over which the channel

transducer is typically calibrated. Since all incoming signals are linear, calibration coefficients are theoretically

accurate over the full measurement range. However, a higher level of confidence is associated with measurements

of demonstrated accuracy made within the calibration range.

Channel measurement tolerances can be defined in terms of required absolute measurement accuracy. For

example, it could be specified that temperature measurements made over the range of Ymin to Y_ be accurate to

± degrees C. Column 7 shows the required overall measurement accuracy ± for each channel in

engineering units over the data range of column 4. The requirements are based on subsequent processed data

needs.

It may not always be desirable to express measurement tolerances in engineering units. It is often necessary to

quantify the accuracy of intermediate processes which occur prior to engineering unit conversion. For this

reason, measurement tolerances are also specified in terms of percent acceptable error over a given measurement

range. For example, wind speed measurement errors can be specified not to exceed ±o.r percent of a given '

measurement range. Column 6 lists the maximum allowable error ±Q., for each channel. Q., is' specified as a

percentage of either half or full measurement range.

Most channels are set up to provide data measurements over a large range to cover all possible conditions.

Typical values, however, occur only within a small portion of the full range. Excursions to range extremes can

be measured, but seldom occur. It is therefore not practical to base calibration requirements on the full data

range. Rather, measurement errors for these types of channels are defined not exceed ±<4n percent of half the

measurement range of 11.z(Y_-Ymm>. Examples are wind speed and blade pressure measurements. Most of the

channels in the table use the half-range error criteria. Some channels, however, require the specified accuracy

across the full measurement range. For these, the required accuracy is ±o.r percent of the full range of Y~­

Ymin. Examples of channels using the full-range criteria are azimuth angle and wind direction, and are identified

with by a (f) in column 6.

The relationship between <4n and is a function of the measurement range, and is defined as:

= Q., Ih(Y_ - Y.,)

= <4n (Y_ - YrmJ

for half-range accuracy

for full-range accuracy

To check acceptable channel drift tolerances, the error level in column 6 defines maximum allowable slope

difference between results of two successive slope calibration sequences. Typically, for each data interval, a pre

and post calibration sequence is conducted. If the percent difference between slopes calculated at each time has

not changed beyond the specified level, then the drift is not significant, and the data is considered valid.

Similarly, maximum allowable offset difference is defined by the maximum measurement accuracy value in

column 7.

All calibration measurements should be made within the required accuracy to a 95% or greater statistical degree of

confidence. This means that there should be at least a .95% probability that calibration measurements fall within

the specified error band. The 95.45% range is defined as ±2Sya where Sya is the standard error (also called the

sample standard deviation). This identity is used to determine the acceptable error range. Maximum allowable

standard errors to achieve the 95% confidence level are shown for each channel in the last column, and were

calculated from:

s = o..m

ya 2

The Unsteady Aero Experiment requires many calibrations to be quickly conducted in the field. To ensure

accuracy and verify calibration results, standard error values from column 8 are compared to those calculated in

the field during Quick-Look calibration sequences. This provides test engineers with an immediate estimation of

calibration validity. A full rigorous statistical analysis could also be conducted in order to provide additional

useful calibration information, including confidence limits for the regression coefficients and individual mean

sample values. Due to limitations imposed by PC-based processing, this is not done in the field, but could be

B-7
post-calculated if required. 95 % confidence limits for least-squares regression slope value m are determined

from:

t.

m S_ m±--~ ..JiM. S..

where t.lnS is the student t distribution for N samples at the .975 level (use 5% significance I 2), and S.. is the

standard deviation ofthe measured X values. Similarly, 95 % confidence limits for the mean sample values can be

determined using standard statistical techniques:

I oc,-X>, Yo ± _ S1" 1+ S 2

-vN-2 ..

where X is the mean of the measured X values and Yo is the predicted value of Y at X = Xo using the resulting

calculated regression slope m and offset b, ie, Yo = mXo + b.

•• For calibrating pressures, the refrence transducer is calibrated to a 99 % confidence level that measurements

can be made to a required accuracy of ± ,(>0133 psi accros the full calibration range of ± .3 psi. The 99.73 %

level is defined as ± 3S1'" which is typically used when calibrating reference transducers from which other

calibrations are derived. For pressure calibrations, required pressure measurement accuracy is 10% of the total

induced pressure.

B-8
Appendix C

Unsteady Aero Experiment Channel Data Rates

C-l
Unsteady Aero Experiment Channel Data Rates

QuicklEXP Filter DeclBW Sample No. Per

Lookrrag Description Setting (NthSeql) Rate DT 144 msec

Number (Hz) (Hz) (Hz) (msec) record

PCM1: North Met Tower (7.5 Kb/s, 34.72 Hz, 28.8 ms):

10111301 20 M Hot Film (Not Used) 5/1 6.94 144.0 1

102/1302 18 M Sonic Channel A (Not Used) 5/1 6.94 144.0 1

103/1303 18 M Sonic Channel B (Not Used) 5/1 6.94 144.0 1

104/1304 18 M Sonic Channel C (Not Used) 5/1 6.94 144.0 1

105/1305 5 M Wind Direction (Not Used) 1 5/1 6.94 144.0 1

106/1306 5 M Wind Speed 1 5/1 6.94 144.0 1

107/1307 10 M Wind Direction (Not Used) 1 5/1 6.94 144.0 1

108/1308 10 M Wind Speed 1 5/1 6.94 144.0 1

109/1309 20 M Wind Direction (Not Used) 1 5/1 6.94 144.0 1

110/1310 20 M Wind Speed 1 5/1 6.94 144.0 1

111/1311 50 M Wind Direction (Not Used) 1 5/1 6.94 144.0 1

112/1312 50 M Wind Speed 1 5/1 6.94 144.0 1

113/1313 5 M Air Temperature 1 5/1 6.94 144.0 1

114/1314 Delta Temperature 1 5/1 6.94 144.0 1

115/1315 5 M DP (Not Used) 5/1 6.94 144.0 1

116/1316 Baro Pressure 1 5/1 6.94 144.0 1

PCM2: Vertical Plane Array (15.0 Kb/s, 69.44 Hz, 14.4 ms):

20110201 VPA Prop Vane WS-l 2 5/2 13.9 72.0 2

202/0202 VPA Prop Vane WS-2 2 5/2 . 13.9 72.0 2

203/0203 VPA Prop Vane WS-3 2 5/2 13.9 72.0 2

204/0204 VPA Prop Vane WS-4 2 5/2 13.9 72.0 2

205/0205 VPA Prop Vane WS-5 2 5/2 13.9 72.0 2

206/0206 VPA Prop Vane WS-6 2 5/2 13.9 72.0 2

207/0207 VPA Prop Vane WS-7 2 5/2 13.9 72.0 2

208/0208 VPA Prop Vane WS-8 2 5/2 13.9 72.0 2

209/0209 VPA PV Hub Height WS-9 2 5/2 13.9 72.0 2

210/0210 VPA PV Hub Height WD-9 2 5/2 13.9 72.0 2

21110211 VPA Bi-Vane WS-12 2 5/2 13.9 72.0 2

212/0212 VPA Bi-Vane WD-12 2 5/2 13.9 72.0 2

213/0213 VPA Bi-Vane Wa-12 2 5/2 13.9 72.0 2

214/0214 VPA Bi-Vane WS-13 2 5/2 13.9 72.0 2

215/0215 VPA Bi-Vane WD-13 2 5/2 13.9 72.0 2

216/0216 VPA Bi-Vane Wa-13 2 5/2 13.9 72.0 2

PCM3: VPA, Local Met, Tower, Turbine (60.0 Kb/s, 277.78 Hz, 3.6 ms):

30110301 VPA Prop Vane WS-lO 2 20/2 13.9 72.0 2

302/0302 VPA Prop Vane WS-11 2 20/2 13.9 72.0 2

303/0303 LSS Azimuth Angle 32 0/54 277.78 3.6 40

304/0304 Yaw Moment 40 0/54 277.78 3.6 40

305/0305 Tower Bending E-W 40 0/54 277.78 3.6 40

306/0306 Tower Bending N-S 40 0/54 277.78 3.6 40

307/0307 Yaw Angle 10 5/11 55.56 18.8 8

308/0308 Generator Power 54 0/54 277.78 3.6 40

309/0309 LSS Speed (Not Used) 40/1 6.94 144.0 1

310/0310 TSI (South) X-Film U (Not Used) 40/1 6.94 144.0 1

311/0311 TSI (South) X-Film W (Not Used) 40/1 6.94 144.0 1

312/0312 TSI (North) X-Film U (Not Used) 40/1 6.94 144.0 1

313/0313 TSI (North) X-Film W (Not Used) 40/1 6.94 144.0 1

314/0314 Sonic Anemometer Ch A (Not Used) 40/1 6.94 144.0 1

315/0315 Sonic Anemometer Ch B (Not Used) 40/1 6.94 144.0 1

316/0316 Sonic Anemometer Ch C (Not Used) 40/1 6.94 144.0 1

C-2
Unsteady Aero Experiment Channel Data Rates (Continued)

QuicklEXP Filter DecfBW Sample No. Per

Look !fag Description Setting (Nth Seq/) Rate DT 144 msec

Number (Hz) (Hz) (Hz) (msec) record

PCM4: Rotating Strain Gages, 80% Pressures (400.0 Kb/s, 520.83 Hz, 1.92 ms):

40111101 Root Flap Bending ~RTFBM-A" 100 0/104 520.83 1.92 75

40211102 Root Flap Bending "RTFBM-B" 100 0/104 520.83 1.92 75

403/1103 Root Flap Blade 2 "RTFBM-2· 100 01104 520.83 1.92 75

404/1104 Root Flap Blade 3 "RTFBM-3" 100 0/104 520.83 1.92 75

40511105 20% Flap Bending "20FBM" 100 0/104 520.83 1.92 75

40611106 40% Flap Bending "4OFBM" 100 0/104 520.83 1.92 75

40711107 50% Flap Bending "50FBM" 100 0/104 520.83 1.92 75

408/1108 60% Flap Bending "60FBM" (Not Used) 75/1 6.94 144.0 1

409/1109 70% Flap Bending "70FBM" 100 0/104 520.83 1.92 75

410/1110 75% Flap Bending "75FBM" (Not Used) 75/1 6.94 144.0 1

411/1111 80% Flap Bending "80FBM" (Not Used) 75/1 6.94 144.0 1

412/1112 85% Flap Bending "8SFBM" (Not Used) 75/1 6.94 144.0 1

41311113 90% Flap Bending "90FBM" 100 01104 520.83 1.92 75

414/1114 Root Edge Bending "RTEBM-A" 100 0/104 520.83 1.92 75

415/1115 20 % Edge Bending "20EBM" 100 0/104' 520.83 1.92 75

416/1116 50% Edge Bending "SOEBM" 100 0/104 520.83 1.92 75

41711117 70% Blade Torque "70TQ" 100 0/104 520.83 1.92 75

418/1118 85% Edge Bending "8SEBM" (Not Used) 75/1 6.94 144.0 1

41911119 Root Torque (Link) "RTTQ" 100 0/104 520.83 1.92 75

42011120 50% Torsion "SOTQ" 100 0/104 520.83 1.92 75

42111121 X-X LSS Bending "LSSX-X" 100 01104 520.83 1.92 75

42211122 Y-Y LSS Bending "LSSY-Y" 100 0/104 520.83 1.92 75

42311123 LSS Torque "LSSTQ-A" 100 0/104 520.83 1.92 75

424/1124 LSS Torque "LSSTQ-B" 100 0/104 520.83 1.92 75

425/1125 85% RTD (Not Used) 75/1 6.94 144.0 1

426/1126 Load Cell for Blade Pull Testing (Cal Only) 7511 6.94 144.0 1

42711127 Pressure #1 StaPTI0, 100% trailing 100 0/104 520.83 1.92 75

42811128 Pressure #2 StaPTI0, 92% upper 100 0/104 520.83 1.92 75

429/1129 Pressure #4 StaPTI0, 80% upper 100 0/104 520.83 1.92 75

430/1130 Pressure #6 StaPTI0, 68 % upper 100 0/104 520.83 1.92 75

431/1131 Pressure #8 StaPTI0, 56% upper 100 01104 520.83 1.92 75

432/1132 Pressure #10 StaPT10, 44% upper 100 0/104 520.83 1.92 75 · 433/1133 Pressure #11 StaPTI0, 36% upper 100 0/104 520.83 1.92 75

434/1134 Pressure #12 StaPTI0, 28% upper 100 0/104 520.83 1.92 75

435/1135 Pressure #13 StaPTI0, 20% upper 100 0/104 520.83 1.92 75

436/1136 Pressure #14 StaPTI0, 14%upper 100 0/104 520.83 1.92 75

437/1137 Pressure #15 S~10, 10% upper 100 0/104 520.83 1.92 75

438/1138 Pressure #16 StaPTI0, 8%upper 100 0/104 520.83 1.92 75

43911139 Pressure #17 StaPTI0, 6% upper 100 0/104 520.83 1.92 75

440/1140 Pressure #18 StaPTI0, 4% upper 100 0/104 520.83 1.92 75

441/1141 Pressure #19 StaPTI0, 2% upper 100 01104 520.83 1.92 75

442/1142 Pressure #20 StaPTI0, 1% upper 100 0/104 520.83 1.92 75

443/1143 Pressure #21 StaPTI0, 0.5 % upper 100 0/104 520.83 1.92 75

444/1144 Pressure #22 StaPTI0, 0% leading 100 0/104 520.83 1.92 75

445/1145 Pressure #23 StaPTI0, 0.5% lower 100 0/104 520.83 1.92 75

446/1146 Pressure #24 StaPTI0, 1% lower 100 0/104 520.83 1.92 75

447/1147 Pressure #2S StaPTI0, 2 % lower 100 0/104 520.83 1.92 75

448/1148 Pressure #26 StaPTI0, 4% lower 100 0/104 520.83 ·1.92 75

449/1149 Pressure #28 StaPTI0, 8% lower 100 0/104 520.83 1.92 75

450/1150 Pressure #30 StaPTI0, 14% lower 100 0/104 520.83 1.92 75

45111151 Pressure #32 StaPTI0, 28% lower 100 0/104 520.83 1.92 75

C-3
Unsteady Aero Experiment Channel Data Rates (Continued)

QuicklEXP Filter DeclBW Sample No. Per

Look fI'ag Description Setting (NthSeql) Rate DT 144 msec

Number (Hz) (Hz) (Hz) (msec) record

PCM4: Continued (400.0 Kb/s, 520.83 Hz, 1.92 ms):

452/1152 Pressure #34 StaPf10, 44 % lower 100 0/104 520.83 1.92 75

"453/1153 Pressure #36 StaPf10, 68 % lower 100 0/104 520.83 1.92 75

454/1154 Pressure #38 StaPf10, 92 % lower 100 0/104 520.83 1.92 75

455/1155 Pressure #18 Sta.PT9, 4% upper 100 0/104 520.83 1.92 75

456/1156 Pressure #11 Sta.PT9, 36% upper 100 0/104 520.83 1.92 75

457/1157 Pressure #11 StaPf8, 36 % upper 100 0/104 520.83 1.92 75

458/1158 Total Pressure Probe, 86 % span 100 0/104 520.83 1.92 75

459/1159 Absolute Reference Pressure 100 0/104 520.83 1.92 75

460/1160 Calibration Pressure (Cal Only) 75/1 6.94 144.0 1

461/1161 Pitch Angle 100 0/104 520.83 1.92 75

462/1162 PCM Voltage Monitor (Quick-Look Only) 75/1 6.94 144.0 1

PCM8: Rotating 30% and 40% Pressures (400.0 Kb/s, 520.83 Hz, 1.92 ms):

801/1201 Absolute Reference Pressure (Not Used) 75/1 6.94 144.0 1

802/1202 Calibration Pressure (Cal Only) 75/1 6.94 144.0 1

803/1203 Spare 75/1 6.94 144.0 1

804/1204 Pressure #1 StaPf1, 100% trailing 100 01104 520.83 1.92 75

805/1205 Pressure #4 StaPf1, 80% upper 100 0/104 . 520.83 1.92 75

806/1206 Pressure #6 StaPf1, 68% upper 100 0/104 520.83 1.92 75

807/1207 Pressure #8 StaPf1, 56 % upper 100 0/104 520.83 1.92 75

808/1208 Pressure #10 StaPf1, 44% upper 100 01104 520.83 1.92 75

809/1209 Pressure #11 StaPT1, 36% upper 100 0/104 520.83 1.92 75

810/1210 Pressure #13 StaPT1, 20% upper 100 0/104 520.83 1.92 75

811/1211 Pressure #14 StaPf1, 14% upper 100 0/104 520.83 1.92 75

812/1212 Pressure #15 StaPT1, 10% upper 100 01104 520.83 1.92 75

813/1213 Pressure #16 StaPf1, 8 % upper 100 01104 520.83 1.92 75

814/1214 Pressure #17 StaPf1, 6% upper 100 0/104 520.83 1.92 75

815/1215 Pressure #18 StaPT1, 4% upper 100 0/104 520.83 1.92 75

816/1216 Pressure #19 StaPf1, 2% upper 100 0/104 520.83 1.92 75

817/1217 Pressure #21 StaPf1, 0.5% upper 100 0/104 520.83 1.92 75

818/1218 Pressure #22 StaPf1, 0% leading 100 01104 520.83 1.92 75

819/1219 Pressure #23 StaPf1, 0.5% lower 100 0/104 520.83 1.92 75

820/1220 Pressure #24 StaPT1, 1% lower 100 0/104 520.83 1.92 75

821/1221 Pressure #2S StaPf1, 2% lower 100 0/104 520.83 1.92 75

822/1222 Pressure #26 StaPT1, 4% lower 100 0/104 520.83 1.92 75

823/1223 Pressure #28 StaPf1, 8% lower 100 0/104 520.83 1.92 75

824/1224 Pressure #30 StaPf1, 14% lower 100 0/104 520.83 1.92 75

825/1225 Pressure #31 StaPT1, 20% lower 100 01104 520.83 1.92 75

826/1226 Pressure #34 StaPf1, 44% lower 100 0/104 520.83 1.92 75

827/1227 Pressure #36 StaPT1, 68% lower 100 0/104 520.83 1.92 75

828/1228 Pressure #38 StaPf1, 92% lower 100 0/104 520.83 1.92 75

829/1229 Pressure #18 StaPT2, 4% upper 100 0/104 520.83 1.92 75

830/1230 Pressure #11 StaPT2, 36 % upper 100 0/104 520.83 1.92 75

831/1231 Pressure #11 St.aPT3, 36% upper 100 0/104 520.83 1.92 75

832/1232 Total Pressure Probe, 34 % span 100 0/104 520.83 1.92 75

833/1233 Pressure #1 StaPf4, 100% trailing 100 0/104 520.83 1.92 75

834/1234 Pressure #2 StaPT4, 92% upper 100 0/104 520.83 1.92 75

835/1235 Pressure #4 StaPf4, 80% upper 100 0/104 520.83 1.92 75

836/1236 Pressure #6 StaPf4, 68 % upper 100 0/104 520.83 1.92 75

837/1237 Pressure #8 StaPT4, 56% upper 100 0/104 520.83 1.92 75

838/1238 Pressure #10 StaPT4, 44% upper 100 0/104 520.83 1.92 75

839/1239 Pressure #11 StaPT4, 36 % upper 100 0/104 520.83 1.92 75

C-4
Unsteady Aero Experiment Channel Data Rates (Continued)

QuicklEXP Filter DeclBW Sample No. Per

Look rrag Description Setting (Nth Seq/) Rate DT 144 msec

Number (Hz) (Hz) (Hz) (InSec) record

PCM8: Continued (400.0 Kb/s, 520.83 Hz, 1.92 ms):

840/1240 Pressure #12 StaPT4, 28% upper 100 0/104 520.83 1.92 75

84111241 Pressure #13 StaPT4, 20% upper 100 0/104 520.83 1.92 75

84211242 Pressure #14 StaPT4, 14% upper 100 0/104 520.83 1.92 75

84311243 Pressure #15 StaPT4, 10% upper 100 0/104 520.83 1.92 75

844/1244 Pressure #16 StaPT4, 8% upper 100 0/104 520.83 1.92 75

845/1245 Pressure #17 StaPT4, 6% upper 100 0/104 520.83 1.92 7S

84611246 Pressure #18 StaPT4, 4% upper 100 0/104 520.83 1.92 75

84711247 Pressure #19 StaPT4, 2% upper 100 0/104 520.83 1.92 75

848/1248 Pressure #20 StaPT4, 1%upper 100 01104 520.83 1.92 75

849/1249 Pressure #21 StaPT4, 0.5% upper 100 01104 520.83 1.92 75

850/1250 Pressure #22 StaPT4, 0% leading 100 0/104 520.83 1.92 75

85111251 Pressure #23 StaPT4, 0.5% lower 100 0/104 520.83 1.92 75

85211252 Pressure #25 StaPT4, 2 % lower 100 0/104 520.83 1.92 75

853/1253 Pressure #26 StaPT4, 4% lower 100 0/104 520.83 1.92 75

854/1254 Pressure #27 StaPT4, 6 % lower 100 0/104 520.83 1.92 75

855/1255 Pressure #28 StaPT4, 8% lower 100 0/104 520.83 1.92 75

85611256 Pressure #30 StaPT4, 14% lower 100 0/104 520.83 1.92 75

857/1257 Pressure #32 StaPT4, 28% lower 100 01104 520.83 1.92 75

858/1258 Pressure #34 StaPT4, 44% lower 100 0/104 520.83 1.92 75

859/1259 Pressure #36 StaPT4, 68% lower 100 0/104 520;83 1.92 75

86011260 Pressure #38 StaPT4, 92% lower 100 0/104 520.83 1.92 75

86111261 Pressure #18 StaPT3, 4% upper 100 0/104 520.83 1.92 75

862/1262 Total Pressure Probe, 50.6% span 100 0/104 520.83. 1.92 75

PCM9: Rotating 63% Pressures, Angle of Attack (400.0 Kb/s, 520.83 Hz, 1.92 ms):

90l/0101 Pressure #11 StaFfS, 36% upper 100 01104 520.83 1.92 75

902/0102 Pressure #18 StaPT5, 4% upper 100 0/104 520.83 1.92 75

903/0103 Pressure #1 StaPT7, 100% trailing 100 01104 520.83 1.92 75

904/0104 Pressure #2 StaPT7, 92% upper 100 0/104 520.83 1.92 75

90510105 . Pressure #4 StaPT7, 80% upper 100 0/104 520.83 1.92 75

906/0106 Pressure #6 StaPT7, 68% upper 100 0/104 520.83 1.92 75

907/0107 Pressure #8 StaPT7, 56% upper 100 0/104 520.83 1.92 75

908/0108 Pressure #10 StaPT7, 44% upper 100 0/104 520.83 1.92 75

909/0109 Pressure #11 StaPT7, 36% upper 100 01104 520.83 1.92 75

910/0110 Pressure #12 StaPT7, 28% upper 100 0/104 520.83 1.92 75

91110111 Pressure #13 StaPT7, 20% upper 100 0/104 520.83 1.92 75

912/0112 Pressure #14 StaPT7, 14% upper 100 0/104 520.83 1.92 75

913/0113 Pressure #15 StaPT7, 10% upper 100 01104 520.83 1.92 75

914/0114 Pressure #16 StaPT7, 8% upper 100 0/104 520.83 1.92 75

915/0115 Pressure #17 StaPT7, 6% upper 100 0/104 520.83 1.92 75

916/0116 Pressure #18 StaPT7, 4% upper 100 0/104 520.83 1.92 75

917/0117 Pressure #19 StaPT7, 2% upper 100 01104 520.83 1.92 75

918/0118 Pressure #20 StaPT7, 1% upper 100 0/104 520.83 1.92 75

919/0119 Pressure #21 StaPT7, 0.5% upper 100 0/104 520.83 1.92 7S

920/0120 Pressure #22 StaPT7, 0% leading 100 01104 520.83 1.92 7S

92110121 Pressure #23 StaPT7, 0.5 % lower 100 0/104 520.83 1.92 75

922/0122 Pressure #24 StaPT7, 1% lower 100 0/104 520.83 1.92 75

923/0123 Pressure #25 StaPT7, 2 % lower 100 0/104 520.83 1.92 7S

924/0124 Pressure #26 StaPT7, 4% lower 100 01104 520.83 1.92 75

925/0125 Pressure #28 StaPT7, 8% lower 100 0/104 520.83 1.92 75

926/0126 Pressure #30 StaPT7, 14% lower 100 01104 520.83 1.92 75

927/0127 Pressure #32 StaPT7, 28% lower 100 0/104 520.83 1.92 75

C-5
Unsteady Aero Experiment Channel Data Rates (Continued)

QuicklEXP Filter DeclBW Sample No. Per

Look trag Description Setting (NthSeql) Rate DT 144 msec

Number (Hz) (Hz) (Hz) (msec) record

PCM9: Continued (400.0 Kb/s, .520.83 Hz, 1.92 ms):

928/0128 Pressure #34 StaPTI,. 44 % lower 100 0/104 520.83 1.92 75

929/0129 Pressure #36 StaPTI, 68 % lower 100 0/104 520.83 1.92 75

930/0130 Pressure #38 StaPTI, 92% lower 100 0/104 520.83 1.92 75

93110131 Pressure #18 StaPT6, 4% upper 100 0/104 520.83 1.92 75

932/0132 Pressure #18 StaPT8, 4% upper 100 0/104 520.83 1.92 75

933/0133 Pressure #11 StaPT6, 36 % upper 100 0/104 520.83 1.92 75

934/0134 Total Pressure Probe, 67.3 % span 100 0/104 520.83 1.92 75

935/0135 Angle-of-Attack, 86% span 100 0/104 520.83 1.92 75

936/0136 Not Used (Ground) 75/1 6.94 144.0 1

937/0137 Angle-of-Attack, 67.3 % span 100 0/104 520.83 1.92 75

938/0138 Not Used (Ground) 75/1 6.94 144.0 1

939/0139 RTD 50% span (Not Used) 100 0/104 520.83 1.92 75

940/0140 Not Used (Ground) 75/1 6.94 144.0 1

94110141 Angle-of-Attack, 34% span 100 0/104 520.83 1.92 75

942/0142 Not Used (Ground) 75/1 6.94. 144.0 1

943/0143 Nitrogen Pressure (Quick-Look Only) 75/1 6.94 144.0 1

944/0144 +15 Volt Power Monitor (Quick-Look Only) 75/1 6.94 144.0 1

945/0145 -15 Volt Power Monitor (Quick-Look Only) 75/1 6.94 144.0 1

946/0146 Angle-of-Attack, 50.6 % span 100 0/104 520.83 1.92 75

947/0147 DC Ground Monitor #1 (V) (Quick-Look Only) - 75/1 6.94 144.0 1

948/0148 Spare 75/1 6.94 144.0 1

949/0149 Spare 75/1 6.94 144.0 1

950/0150 Spare 75/1 6.94 144.0 1

95110151 Spare 75/1- 6.94 144.0 1

952/0152 Spare 75/1 6.94 144.0 1

953/0153 Absolute Reference Pressure 100 0/104 520.83 1.92 75

954/0154 Calibration Pressure (Cal Only) 75/1 6.94 144.0 1

955/0155 Spare 75/1 6.94 144.0 1

956/0156 Spare 75/1- 6.94 144.0 1

957/0157 Spare 75/1 6.94 144.0 1

958/0158 Spare 75/1 6.94 144.0 1

959/0159 Spare 75/1 6.94 144.0 1

960/0160 Spare 75/1 6.94 144.0 1

96110161 Spare 75/1 6.94 144.0 1

962/0162 Spare 75/1 6.94 144.0 1

C-6
Appendix D

Design and Experimental Results for the 5809 Airfoil

D-l
AIRFOIL§). ][NOORPORATED

61T WILLOW OAKS BOULEVARD

RAMPI'ON. VIRGIlinA a3600

(1104) .1-9338

DESIGN AND EXPERIMENTAL RESULTS rOR THE sao, AIRFOIL

Dan M. SO.lrs

larch un

ABSTRACT

A Zl-perc.nt-tblck, la.lnar-flow airfoil for horllontal-aal. wlndturbln. application., the sao,. ha. bl.n d••lvn.d and analyl.d

thlor.tlcally and ••rlfl.d 'Ip.rl••ntally In lh. low-lurb.l.nc. wind tunnel

of th. D.lft Unh.rslt, of T.chnolog, Low Spud Laboratory, Th.

Nlth.rland•. Thl two prl.ar, ob'.ctl••s of r••traln.d .all.a. 11ft,

In ••n.lti•• to roughnls" and low profl1. drag ha •• b••n achi'.ld. The

airfoil al.o elhlblt. a docl1 ••tall. Co.parl.on. of th. th.or.tlcal and

••p.rl.ental r••ult••how·good agr••••nt. Co.part.on. with oth.r airfoil.

111u.trat. thl re.traln.d .aal.ua 11ft co.fflcl.nt a. will a. the 10w.r

profll.-drag co.fflcl.nt•• thus conflr.lng the achl•••••nt of the prl.ary"

ob'ecthes.

INTRODUCTION

Th•••,orlty of the airfoil. In a.e on borllontal-aal. wind lurblne.

today w.re originally .e••loped for airplane.. The de.lgn requlr•••nt. for

th••• airfoil•• prl.arll, National Ad.l.ory Co..ltt•• for A.ronaallc.

(NACA) and National A.ronaatlc. and Spac. Ad.lnl.tratlon (NASA) alrfol11

(refs. 1 throagh U, art .1gnlficantl, dlfftrtnt fro. thou lor 'wl ndturbln. airfoils. Accordingly. two .It. of thick airfoil. wlrl d•• lgn.d,

. a s i n, the ••thod of rlflrencls 7 and •• ,plcifically for horllontal-alll

wind-tarblne application•. (511 rlf. ,.) Th. aa'or, di.tlngai.hing

f •• tur. betw••n the two ••t. il the aaliaaa 11ft co.fflci.nt. of the

~lrfolll for the oatboard portion of the wlnd-turbln. blad.. Th. flr.t I.t

produc •• r.l.tl••l, low (-r••trained-) .aal.ua 11ft eo.fflcl.nt. oatboard

whereal the .Icond I.t produci' .a.lau. lift co.ffici.nt. outboard which

are a.z hlghlr than tbol. produc.d b, thl fir.t I.t.

In con'unctlon with thl••ffort, the prlaary airfoil (0.7S blad.

radial Itatlon) of thl flr.t ••t was ••1.ct.d fOf ••p.rl••ntal

••rlflcatlon. An In."tlgatlon wa. conduct.d in the low-tarbal.nc. wind

tunnel of the Delft Unl••r.lty of T.chnolo,y Low Sp••d Laboratory

(rd . 10). Th. N.thuland•• to obtain the baslc, loW-lp••d, two-dl••n.tona1

a.rod,namic charact.ri.tlc. of this alffoi1. Thl r••alt. ha •• b••n

co.pared with th. pr.dlctlon. fro. th•••thod ot r.f.r.nci. 7 and. and

a1.0 with data fro. anoth.r low-tarbal.nc. wind tann.l for oth.r alrtoll•.

Th. Ip.clflc taskl p.rfor••d andlr thl••tady art dl.crlbld in ·Solar

Ener,y Re5.arch In.tltat. (SERI) Subcontract Na.blr HI-6-0607S-1.

D-2
EIPERI"ENTAL PROCEDURE

WIND TUNNEL

Thl low-turbulinci wind tannll (rlf: 10) of thl Dilft Uni.lrlity of

Tlchnology Low Sp'ld Laboratory, Thl Nlthlrland., 1. I ClO.ld-throlt,

11.011-return, at.olphlrlc tunnll tflg. 3). Thl turbulinci 11•• 1 in thl

t.lt I.ction .arl•• froa J.D~ p.rclnt at 10 .1. (33 ft.I.) to 0.04 p.rclnt

at 60 .,. (200 ft.II).

Th. octagonal t.lt I.ctloa 1. 110.0 ca (7D.17 In.) wid. by 125.D e.

(4'.21 In.) high. Ellctrically actaatld tarntablll pro.ldl pOlltloninq IDd

Ittachalnt for thl two-dl.lnllonl! aod.l. Th. tarntahl•• ar. flush with

the top Ind botto. tunn.l Willi Ind rotltl with thl .od.l. Thl ali. of

rotltlon colncldld with thl quart.r chord of the aod.1 which wal .ountld

.Irtlcally bltw.ln the tarnta~I••. CSII fig. 4.) Thl 9api bltw.ln thl

.odel Ind the turntlbll. wlrl ••al.d.

KDDEL

Th. Ila.lnua, wlnd-tannll aodll WI. conltruct.d b, the D.utlchl

Forlchungl- und Vlrlach.lnstllt fair taft- und lavaflhrl •. v. (DrVLR),

Braun.ch••lg, Fldlral R,publlc of Glraany. Thl aod.l had a chord of

'00.10 •• (~3.'~~ In.Joand a .pan of 1~41 _ (.'.13 In.L Chordwl••

orlflc•• wlr. loclt.d in the upp.r Ind low.r lurfac'l to on. Iidl of the

.ld.pln at lh. Itlgg.r.d pOlltlons 11st.d In·tabl. III. Spanwll' orlfie.s

w.rl locatld In thl upp.r larfaci only In ordlr to aonltor lh. twodi.I•• Ionlllty of the flow It hl0h anolll of attact. All the oriflc'l vlre

0.4D .. (0.01' In.) In dll••t.r with thllr a ••• plrp.ndlculaf to the

surflCI. Thl a.llur.d aod.l contoar wa. o.nlrally within 0.1 a.

(0.004 In.) of lh. prl.crib.d shap•.

VAlE RAIE

A total-pr'llur., • Italic-pr•••ur., and an I~t.grlting watl flte

Wlrl aountld on I Itrut ••tw.en thl tunnll Ildlwalll (figl. 4 and 5). Thl

Itrut coald bl po.ltlon.d Ipanwil' and .tr.aawill in thl tl.t I.ction.

Mo••••nt of thl .trut ,ro,lded pOlltlonlno of the watl rat•• noraal to thl

Ildlwalll. Th. tip. of thl total-pre••ar. tub'l wire locatld

down.tr.a. of thl trailing Id91 of the .odll. Thl d.tail. of thl watl

rat•• arl Ihown In flgur •• , Ind 7. Thl lnt.,ratln, wat. rat. WI. not ulld

in thl. in.l.tlgatlon.

INSTR1R'1ENTAT ION

"11.arl••ntl of thl basle tunn.l prlssar.l, the Itatic prlssurl. on

thl aodll lurfacl., and the watl-ratl prls.ar.1 were aade by a aultitub.

aaDo••tlr whleh was read .aato.atically a.lng photoel.ctric cIIII. Dati

wlr. obtaln.d and record.d by an Illctronlc dala-acqaisltlon IYlt••.

D-3
KETHODS

Thl .tatic-prlssurl •• asur •••nt. on thl .odll surface were reducld to

.tandard prl••url cOlfficilnt. and nU.lrically intlgratld to obtain .ection

normal-force coefficients and section pitehing-ao.ent coefficients about

thl quarter-chord point. Section profil.-drag coefficients were computed

froa the wake-rake total and .tatic pressures by the method of

reflrencl 11. Standard, low-Ipe.d, wind-tunnll boundary corrections

(ref. 13) ha., beln applied to thl data. Thl folloWing procldurl was used.

The uncorrect.d for~., aoa.nt, and prl.sarl cOlffici.nt. are r.f,rrld to

th. apparent dynamic pressurl as ••asur.d tunnel ••pty at the .odll

position. Th. lift, profil.-drag, pitching-aoment, and airfoil pressure

coefficients and the angl. of attack art th.n corr.et.d by the aethod of

r.ference 13. Thl corrlctld .alaes arl plottld. Finally, as a check, the

corr.ctld airfoil pr.s5url distribution is nU.lrically intlgrated to obtain

th. eorrlcted nor.al-forc. (and pitching-aoaent) cOlffici.nt which,

toglther with the correctld profil.-drag co.fficilnt and angl. of attack,

yi.1ds the corr.ct.d 11ft cOlffl~lent (and chord-fDrc. co.fflcilnt).

At high ang II. of·· a t tack, thl wah b.co... widlr than the wake rake.

Vh.n this occurs, the drag is obtain.d fro. a parabolic ••trapolation of

the aeasurld watt prlslur.s. At 1.ln highlr ang1.s of attack, the totalprelsurl co.fflclent••Ia.ur.d In the watt blco•• n.gati•• , .ating .

calculation of the drag i~polsibl.. In thIS' cas.s, an uncorr.cted

prof ill-drag co.fficl.nt of 0.3 (.sti.at.d froa rlf. 14) is alsumld.

TESTS

Thl aod.1 was t.stld at R.ynolds nu.b.rs bas.d on aJrfoll chord froa

1,000,000 to 3,000,000. Thl .od.1 wa. tlst.d s.ooth (transition frel) and

with transition fi.ld by roughn.ss at 1.02c on thl upplr surfacI and 0.05c

on the low.r surfac.. Thl grit roughnlss was liSld by the ••thod of

rlferencI 15 and spars.1y distributld along 3-.. (O.l-ln.) wide Itrlps

applied to the aode1 with lacqu.r. (SI. tabl. IV.)

Starting froa lero degrels, thl angll of attack was increasld until

the .ntire upp.r surfacI was slparatld and th.n d.crlasld In order to

d.termine hysterlsil. Th••a•• proc.durl was follow.d for the nlgati.1

ang1 •• of attack. For the R.ynold. nuablrs of 2,500,000 and 3,000,000, the

.tatic prlssarl. on thl upp.r lurfac. could not b•••asur.d by the

.anoa.ter at high angl.1 of attact b.caul. the diff.r.nc.1 b.twe.n thai'

pr.ssur.s and thl fr ••-str.a. static pr ••sur. wlr. too gr.at.

For ••••ral t.st runs, thl _odll lurface. w.rl coatld with oil to

determin. the location. al well al the natur., of the boundary-lay.r

transition froa laainar to turbulent flow (r.f. 16). Tran.itlon was also

located using a probe containing a .icrophonl, which was positioned near

the llading Idge and then aO.ld .lowly downstr.a. along the aod,l .urflce.

Two span stations. corrllponding to the watl-rakl position and thl

chordwisl orificl row, wert lur.lyed. The beginning of the turbulent

boundary layer wal d.t.ct,d II an incr•••• in noill 1••• 1 o.lr that for the

1aainar boundary lay.r which wal '5~lntial1, si1lnt. (SI. ref. 17.)

D-4
Two turbulator., li9-lag tap. (rlf. tl>, wI.rl placid on thl model,

one betweln O.43c and O.4'c on thl upplr .urfaci and thl other betwlln

O.42c andO.44c on the low.r surface, In ord.r to detlrminl their efflct on

laminar s.paration b~bbl.s and s.ction characteristics. The d.tairs of the

0.2'-a. (O.DtO-ln.) thict tape are Ihown in the followin9 stitch.

J_-.A.

I ''''ftI

1

PRESENTATION OF RESULTS

Thl principal r.lult. of thl. In.lstigation arl prlslntld in thl

following fi9urls:

PreSlurl distributions for R • 2,000,000. Arrows indicatl dir.ction

of angl.-of-attack chang. (for dltlr.inatlonof hyst.rlsi.)

Oil-flow photographl of upplr lurfaci for R • 1,000,000

Oil-flow photograph. of upplr lurfaci for R • 2,000,000

Oil-flow photographs of upp.r surfaci for R • 3,000,000

Oil-flow photographl of lowlr lurfaci for R • l,aOO,ooo .... Oil-flow photographs of lowlr lurfac. for R • 2,000,000

Oil-flow photographs of lowlr lurfaci for R • 3,000.000 ....

Transition location. Bar. I.tlnd fro. b.ginning ~o .nd of

transition. . . . . . . . .. . •..•

Spanwisl drag co.fflcl.ntl for R • 2,000,000 ..

Section eharactlrl.t(cs .....•...

Effect of roughnll. on Iletion charaetiristici ..

Eff.ct of ·.turbulators on drag cOlfflcilnt. . . . . ...

Efflct of turbulator. on .'lction charact.ristici for R • 1,000,000 .

Co.parllon of theorltical and I.plrl••ntal prll.url di.trlbutions

Co.parllon of th.oriticiland I.plri.lntal 'Ictlon charlctiriitici

with trlnsltion frel ...............•.......

Co.plrl.on ofthlor.tlcil and I.plri.lntal ••ctlon charactlri.tlc.

with tran.ltion fi.ld .. . . . . . . . . . •. . .

Co.parllon of .Ictlon chlractlriltlcs of SI09 and NACA 4421 airfoil.

for R • 3,000,000 ..•..•....•......•...

Comparl.on of s.ction charactlrl.tic. of SI09 and NACA 23021

airfoil. for R • 3,000.000 ..••..••.••......

D-S

Fi9ure

I

,

10

1t

12

13

14

IS

16

17

11

19

20

21

22

23

24

25














Appendix E

Wind Tunnel Tests of the 8809 Airfoil Model

E-l
T . H . E

OHIO

SlATE

UNIVERSITY

Aeronautial and Astronautical

Research Laboratory

WIND TUNNEL TESTS OF

THE S809 AIRFOIL MODEL

G. M. GREGOREK

M. J. HOFFMANN

K. E. KULH

2300 West Case Road

Columbus.OH 43235-1949

Phone 614-292-5491

THE AERONAUTICAL & ASTRONAUTICAL RESEARCH LABORATORY

THE OHIO STATE UNIVERSITY

COLUMBUS. OHIO

APRIL 1991

Prepared for: SOLAR ENERGY RESEARCH INSTITUTE

MIDWEST RESEARCH INSTITUTE

CONTRACT XL-9-19011-1

E-2
FOREWARn

This is the. Final Report on Midwest Research Institute Grant

XL-9-19011-1 Entitled ''Wind Tunnel Testing on the 8809 Airfoil Model".

(OSU Research Foundation Project 721623). Hr. Sandy Butterfield was

the Technical Monitor for the Solar Energy Research Institute for the

period November 1988 to June 1989.

E-3
TABLE 01' CONTENTS

ABSTRACT

I. INTRODUCTION

II. RESEARCH PROGRAM

A. Test Program

B. Experimental Facilities

C. Data Acquisition And Reduction

III. RESULTS AND DISCUSSIONS

A. Steady State Test Sequence

B. Vane Calibration

C. Unsteady Vane Measurements

IV. SUMMARY

APPENDICES

E-4

page

iii

1

3

3

3

5

6

6

8

10

12
I ·

FIGURE j

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

LIST ·OP PIGURES

LOW SPEED WIND TUNNEL SCHEMATIC

OSCILLATORY SYSTEM DESIGN

5809 MODEL SCHEMATrC

DATA ACQUISITION AND REDUCTION SYSTEM

S809 SURFACE PRESSURE DISTRIBUTIONS

S809 LIFT COEFFICIENT VS ANGLE OF ATTACK

S809 MOMENT COEFFICIENT VS ANGLE OF ATTACK

S809 DRAG COEFFICIENT VS ANGLE OF ATTACK

S809 DRAG POLAR

CALIBRATION OF ANGLE OF ATTACK PROBE VS

MODEL ANGLE

PROBE ANGLE VS TIME AT Real.OX106

PROBE ANGLE VS TIME AT Re=O.74xl0 6

PROBE AND MODEL ANGLE OF ATTACK VS TIME

AT 0.2 Hz

PROBE AND MODEL ANGLE OF ATTACK VS TIME

AT 0.6 Hz

PROBE AND MODEL ANGLE OF ATTACK VS TIME

AT 1.2 Hz

E-5

PAGE
ABSTRACT

A wind tunnel test program to calibrate a vane-type angle of

attack senso~ that is in use on the rotor of the HAWT undergoing ,

field tests at Rocky Flats was conducted in the 3'x 5' Subsonic

Wind Tunnel of The Ohio state University. The sensor was mounted

on a boom extending from the leadinq edge of an 18" chord, twodimensional model of the S809 airfoil. static calibration of the

vane produced two distinct linear relationships between vane

angle and model angle of attack. Between a model angle of attack

from -5· to +7-, this linear calibration is represented by:

Qmodel=0.590* Qprobe + 0.4-;

while the model angle reqion from ,+7 - to +15- is represented by:

Qmodel=0.799 * Qprobe - 2.0-.

'When the vane was disturbed from it's equilibrium position during.

tunnel tests with the model at a fixed anqle of attack a damped

oscillation with period of 0.10 seconds was recorded, with time

to damp to half amplitude of 0.073 seconds. Vane response was

also measured as the model was sinusoidally oscillated ±3- about

a mean angle at frequencies of 0.2, 0.9, and 1.2 Hz. To extend

the data base on the S809 airfoil, surface pressures and wake

total pressure surveys were measured durinq the steady state

calibration of the vane. These pressures were integrated to

yield lift pitchinq moment and total draq coefficients at the

test condition of Re=1.0xl06•

E-6
I. INTRODUCTION

The 5809 airfoil is an airfoil tailored for Horizontal Axis

Wind Turbine (HAWT) rotors. It is presently being used on the

HAWT at Rocky Flats and .i s undergoinq extensive field tests.

This rotor on the field test machine has a vane projecting from '

the leading edge of the airf~il to 'be used as an anqle of attack

measuring device. The upwash from the airfoil alters the flow

field of the vane, necessitating a calibration .of the vane versus

model angle of attack. The purpose of the experimental program

conducted at the Aeronautical and Astronautical Research Laboratory (AARL) of The Ohio state University (OSU) reported here, is

to provide this calibration for both steady and unsteady flow

conditions. In addition, during the steady state tests, surface

pressures are obtained and wake pressures measured to supplement

the existing data base on the aerodynamic characteristics of the

S809 airfoil.

The OSU 3 1x 51 Subsonic Wind Tunnel was used for the test

program. Test conditions were at a Reynolds number of 1x106

based on an 18" model chord. Steady state pressures were measured at angles of attack from.-S- to +15- and were reduced to

lift and pitching moment coefficients_ A wake survey probe

provided total drag for the steady state test sequence. Unsteady

information was obtained by 'oscillating the model with a sinusoidal wave form of amplitude ±3-. During the oscillations both

vane angle and model angle of attack were recorded. These data,

coupled with the steady state calibration of the vane versus

model angle of attack provide the needed calibration.

E-7
A description of the e~perimental program, wind tunnel and

model, fabricated earlier from the same mold ·used to produce the

HAWT rotor being field tested, follows. Results of the test are

presented in .both tabular and graphic form and include a short

test sequence of the dynamic response of the vane. An Appendix

includes the airfoil coordinates and location of the pressure

taps on the model to complete the report.

&8
II. RESEARCH PROGRAK

A. Test proqram

The main purpose of the present test program was the calibration of the angle of attack vane relative to the airfoil angle of

attack. These calibrations were to be performed in steady state

and in an unsteady condition with the airfoil oscillating sinusoidally at a nominal ±3- angle of attack. During the steady

state tests, surface pressures were to be recorded as well as

airfoil and vane angle of attack to provide pressure distributions which could be integrated to lift, moment and pressure drag

coefficients. A wake survey would also be conducted to determine

the total drag of the airfoil. These steady state data were to

supplement data obtained from the model in an earlier test series.

All tests were conducted at a nominal Reynolds number of 1xl06

based on the 18" model chord.

B. Experimental Pacilities

The Subsonic Wind Tunnel at AARL is shown schematically in

Figure 1. It is an open-circuit, atmospheric wind tunnel of the

Eiffel type, powered by a 125 hp AC motor driving an 8' diameter,

6 blade fan. · The blade angle can be set, manually, to produce

velocities from 20 to 200 ft/sec. Test section turbulence level

is low; four 40 mesh seamless stainless steel screens and a 4

inch thick honeycomb of 1/4 inch cells upstream of the contraction maintains' a turbulence level measured below 0.1%_·

The test section geometry is rectangular, with filleted corners; dimensions of the test section are 55" wide and 39" high.

E-9
Because of ' this .or i e nt at i on , two dimensional airfoil models are

mounted vertically in the facility. A horizontally traversing

single total pressure probe is used to survey the wake behind the

airfoil to measure total airfoil drag • . Wind tunnel test conditions are monitored by a single total probe mounted off the wall

and by two static ports mounted in each side wall as shown in the

schematic.

Two pressure sensing systems can be used to measure airfoil

pressure distributions. For steady state measurements a single

pressure transducer is coupled to a 48 port scanning system

located outside of the wind tunnel to make the surface measurements. When unsteady pressure are required, two electronically

scanned pressure modules can be mounted inside the model to

reduce the length of pressure tubing and to provide the necessary

rapid response.

These unsteady airfoil tests are performed on pressure tapped

airfoil models mounted on the oscillating rig shown in Figure 2.

The rig is driven by a 5 hp AC motor that is controllable over a

wide range of frequencies. Because large airfoil models are

being studied, frequencies from 0.1 to 2 Hz are pertinent for the

wind turbine applications of interest. Amplitude and wave form

during the oscillation are controlled by specially designed face

cams. Sinusoidal wave forms and other more complex wave shapes

are available.

The two dimensional model of 18" chord studied in this experimental series has the specially designed S809 contour. It's

coordinates are listed in Table I of the appendix. Table II in

the appendix gives the location of the 31 pressure taps used in

the steady state surface pressure measurements. A sketch of the

&W
model showing the location of the total pressure probe and the

angle of attack vane is presented in .Figure 3.

c. Data Acquisition ADd Reduction

As noted in Fiqure 4, the data from each test run was recorded

by an IBM PC-XT and processed by the AARL Harris Haoo computer.

The output from the wind tunnel pressure transducers, vane and

model angle of attack sensors, electronically scanned pressure

module, and wake probe pressure and position were recorded on the

PC disc for each test run. Prior to the start of each run a

calibration ~f -all the pressure instrumentation was also printed

Qn the disc. A test run for this test program consisted of one

of two modes: a steady state mode in which the surface pressures

and wake total pressure survey were obtained at a fixed model

angle of attack, and an unsteady mode d~ring which the model ·was

oscillated ±3- about a mean angle of attack at a specific frequency and the angle of attack sensors measured as a function of

time. During the unsteady test mode, the surface pressures were

not measured.

As a series of test runs are completed and stored on disc, for

example, after 5 steady state angles of attack or frequencies of

oscillation, the electronic data was processed by the Harris H~OO

into engineering units to produce the required hard copy tables

and plots of the test results. These surface p~essure distributions, lift, drag, and pitching moment coefficients as a function

of angle of attack for the steady case and vane and model angle

of attack time-histories were available within a few minutes of

completion of a test sequence.

B-11
xxx_ RESULTS AND DXSCUSSXOHS

A_ Steady State Test Sequence

sixteen surface pressure distributions taken during an angle

of attack sweep from a nominal -8- to +19- are presented in

Figure 5. A legend accompanies each distribution to give the

angle of attack, test Reynolds number, lift coefficient, pressure

drag coefficient and pitching moment coefficient. Note that the

triangles with the vortex pointing up represent the upper surface

pressures while the triangular symbols with the downward pointing

vortex are the lower surface pressures.

The pressure distributions can provide insight into the aerodynamic behavior of the airfoil. For example, Run 558, the first

distribution presented is at a negative angle of attack (-8.1-)

so the lower surface pressures are negative yielding a negative

lift coefficient (Cl=-0.57). Further, the airfoil is near its

stall at this negative angle as determined by the constant pressure plateau of Cp=-0.3 representing flow separation for the aft

50% of chord. When the angle of attack increases 2- to -6.1·,

the lower surface pressure is now attached, with the pressure

plateau eliminated and the trailing edge pressure becoming positive. As the angle of attack becomes more positive, the lower

surface leading edge pressure spike gradually decreases, disappearing near -2- and providing smooth pressure distributions on

both upper and lower surfaces, favoring natural laminar boundary

layer development for the forward 45' of airfoil chord. The

favorable pressure gradients persist on both surfaces until

nearing 5·, where a pressure spike begins to develop in the upper

surface leading edge. This pressure peak increases with angle of
attack. At 7.1· the flow is attached up to the trailing edge,

but by 9.2· the flow has separated past the 55t chord of the

upper surface. In spite of this flow separation the low pressure

spike' continues to increase, with a corresponding modest increase

in lift coefficient until complete separation occurs on the upper

surface as shown at angle of attack 16.8·, and the lift coefficient falls.

The integrated surface pressure distributions are presented in

Figures 6 to 9. Figures 6 and 7 'indicate the lift and pitching

moment coefficient versus angle of attack. The total drag coefficient obtained from integration of the momentum deficit in the

wake is illustrated in Figure 8; the pressure drag coefficient

is not shown since the pressure taps- on the model were not felt

to be sufficient to determine a reliable value of pressure drag.

A drag polar is given in Figure 9. From this information, perti-·

nent aerodynamic characteristics for this airfoil are summarized

in Table I below:

'1'ABLB I

5809 Measured Aerodynamic Coefficients At Re= 1.05 x 106

Clmax 0.91 @ 0=7· , 1.03 @0=15·

dCl/da 0.121 '

alo -1.0

CMo -0.035

Cdmin 0.0069 @ a=5·

(Cl/Cd)mx 107 @a=5·

-0.57 @a=-S·

E-13
Table II lists the complete aerodynamic coefficients as a function of model angle of attack. The table includes the vane angle

of attack.

TABLB XX

SERI Steady State Reduced Data

RUN tI °model °vane Cl Cdw em Rexl06

557 3.5 5.42 0.545 0.0078 -0.0449 1.07

558 -8.1 -13.38 -0.574 0.0742 0.0028 1.06

559 -6.1 -10.66 -0.547 ------ 0.0161 1.06

560 -4.2 ~7.75 -0.416 0.0117 -0.0176 1.06

561 -2~6 -4.98 -0.198 0.0114 -0.0266 1.06

562 -0.5 -1.45 0.056 0.0109 -0.0341 1.06

563 1.5 1.70 0.286 0.0102 -0.0373 1.06

564 3.6 5.33 0.535 0.0091 -0.0426 1.06

565 5.1 7.87 0.737 0.0069 -0.0510 1.05

566 7.1 11.41 0.914 0.0088 -0.0385 1.05

567 9.2 13.96 0.946 0.0525 -0.0396 1.05

568 11.2 16.50 0.967 ------ -0.0314 1.04

569 12.7 18.34 1.000 ------ -0.0279 1.04 ·

570 14.9 21.17 1.029 ------ -0.0440 1.05

571 16.8 22.76 0.723 ------ -0.1272 1.04

572 18.6 24.33 0.726 ------ -0.1268 1.03

B. Vane Calibration

Steady state Calibration

From the steady state tests described above, the calibration

of the sensed angle of the vane compared to the geometric angle

of attack can be obtained. Figure 10 presents this data for the

angle of attack ranging from -8- to +19-_ It can be noted that

this curve appears to have two distinct linear portions, represented by the two equations below:

From -5-<0<+7- 0model - .590*Oprobe + 0.4

From +7·<0<15- 0model = .799*ap r obe - 2.0

E-14
••

The two equations represent the experimental data with to.1· in

their range of applicability.

The two segment behavior of the vane calibration is related to

the loss of circulation as the flow separates from the airfoil.

Referring back to th~ pressure distributions, the angles of

attack between -5· and +7· all have positive pressures at the

trailing edge, indicating attached flow to the trailing edge and

a corresponding linear increase in lift with angle. At angles

above 7·, up to 14.9·, a low pressure plateau exists on the upper

aft airfoil surface with a leading edge pressure spike increasing

with angle. The pressure spike collapses at "16.8· and, again,

the vane calibration re~~ects this flow behavior by departing

from the linear equation. A similar separation pattern exists at

the negative angles of attack when the angle exceeds -5·, with

the vane calibrations again becoming non-linear.

Vane Response

A limited test sequence ~as per£ormed to examine the response

of the vane. With the model fixed at an angle of attack and the

tunnel operating, a clip restraining the vane was released,

allowing the vane to respond to the flow field about the airfoil.

Figures 11 and 12 illustrate the probe angle of attack as a

function of time. The vane responds with a damped oscillation as

shown. Two other trials at this wind tunnel test condition were

made, then two more such vane response checks were made at a

lower speed, corresponding to Re c O.74X106• Table III summarizes this response data.

~lS
TABLB X:tJ:

VANE RESPONSE

RUN I PERIOD AMPLITUDE TIME TO 1/2 AMP.

(sec) (deg) (sec)

574 0.107 9.35 0.072

575 0.100 9.25 0.075

576 0.097 7.0 0.073

579 0.120 9.5 0.103

The average of the three trials at Re= 1x106 yields an oscillation period of 0.101 seconds; frequency of 9.9 Hz with 0.073

seconds and 0.·72 cycles to damp to half amplitude • . Only one of

the vane response tests at the lower speed was recovered (Run

- 579). This single vane test indicates a period of 0.120 seconds

with a frequency of 8.33 Hz and 0.103 seconds and 0.85 cycles

required to damp to half amplitude.

The ~longer period and decreased damping of the vane found

during the lower speed tests are attributed to the decrease in

dynamic pressure. Although vane inertia about the near frictionless period remains the same, the restoring aerodynamic moment is

decreased.

c. Unsteady Vane Xeasurements

Four tests were made with the airfoil oscillating ±3· about a

7· mean angle of attack. The frequency of this sinusoidal motion

was varied from 0.2, 0.6, 0.9 and 1.2 Hz. Those of the time

histories of model and vane angle of attack are shown in Figures

13, 14, and 15; the data for the 0.6 Hz test run could not be

recovered because of instrumentation problems.

In all three cases the vane angle lags the sinusoidal oscillaE-16
••

.t i ons of the models. Examination of the digital data for each

test case indicates a phase lag of approximately 0.28 seconds for

the 0.2 Hz test, 0.05 seconds for the 0.9 Hz test and 0.03 seconds for the. 1.2 Hz case. These values for phase shift of the

vane time-history must be taken as approximate times; 'however,

since both angle of attack sensor outputs appear to"have a sizable noise level. The follower on the face cam that drives the

model angle of attack causes some ·chatter" in the model angle of

attack signal. When that "chatter" is coupled with the motion of

the vane that has the damped oscillation noted earlier, the vane

and model outputs are difficult to interpret.

Attempts to use the steady state calibrations of Fiqure '10 to

predict the model angle of attack from the vane output met with

mixed success. By applying the phase shift, using the static

ca~ibration and the vane measured angle, the model angle of

at~ack many times could be predicted within to.2· of the measured

model angle. At other times, the predicted values were more than

1·- off, usually due to noise in the digital output~ It appears

that a smoothing routine must be applied to the vane output to

reduce the scatter in the vane output data. As of this writing

it does appear that the static calibrations may be used to predict the model angle of attack when the frequency dependent phase

lag of the vane is used to adjust prediction•
xv_ SUHKARY

A two dimensional model of the S809 airfoil has been tested in

the asu 3 1x 51 Subsonic Wind Tunnel. The experimental program

was performed to calibrate an angle of attack vane mounted on the

model and to provide additional aerodynamic data on the S809

characteristics.

Under steady state conditions, the vane angle versus model

angle resolved into two linear regions. In the model angle of

attack range from -5- to +7-,

Qmodel= 0.590 * Qprobe + 0.4

In the model angle of attack range from +7- to +15-

Qmodel= 0.799 * Qprobe - 2.0

In terms of probe angle measurements, the first equation applies

from a probe angle of -9- to +11-, the latter equation applies

when probe output is +11- to +21-. outside these angle of attack

ranges, the calibrations are non-linear.

Unsteady tests measured the dynamic response of the vane when

freed sUddenly. from a restraint while the tunnel was operating

and the model held at a ·fixed angle of attack. The period of the

damped oscillating response averaged 0.101 seconds for three

response trials at Re = lX106• Time to damp to half amplitude

averaged 0.073 seconds. At a lower Reynolds number (.74X106) a

single trial resulted in increase in both the period and half

amplitude time. A second unsteady series of tests put the model

in sinusoidal motion. The vane followed this motion, lagging the

model by approximately .28, .05 and .03 seconds for the three

recorded oscillation frequencies of 0.2, 0.9 and 1.2 HZ, respecE-18
tively. Application of the steady state vane calibration using

these phase laqs appeared to yield adequate predictions of model

anqle of attack for selected trials. However, both sets of

sensed.·anqle data, vane and model, require smoothinq and additional analysis to improve the calibrations.

The measured steady state pressure distributions verified the

favorable laminar flow pressure gradients and the limited maximum

lift designed into the 8809 airfoil for KAWT applications. The

minimum draq coefficient measured was Cd - 0.0069, produclnq a

maximum lift to draq ratio of 107 at a - 5-. At a - 7- flow

separation occurred to initiate a limited maximum lift with full

separation from the upper surface at a - 14.9- holdinq the .maxi -

mum value of lift coefficient to Cl - 1.029.

E-19




















APPENDICES

E-40
D

UO

, . ..

• .DO .11 ... .11

lIe

E-41

.Ia
TABLE III 880t TAP I'J:LB

SERI S809 18 INCH CHORD MODEL FOR 3X5

PRESSURE TRANSDUCER MODEL TAP X/C Y/C

PORT NUMBER NUMBER

1 1 1.0000000 -0.0000400

2 2 0.9180000 0-.0167000

4 3 0.7970000 0.0395000

6 4 0.6789000 0.0616000

8 5 0.5588000 0.0854000

10 6 0.4394000 0.1006000

11 7 0.3594000 0.1004000

13 8 0.1984000 0.0831000

14 9 0.1389000 0.0705000

15 10 . 0.0992000 0.0595000

16 11 0.0792000 0.0527000

17 12 0'.0589000 0.0448000

18 13 0.0398000 0.0357000

19 14 0.0189000 0.0228000

20 15 0.0089000 0.0151000

21 16 0.0027000 0.0072000

22 17 0.0000000 0.0000000

23 18 0.0040000 -0.0091000

24 19 0.0111000 -0.0140000

25 20 0.0210000 -0.0200000

26 21 0.0421000 -0.0314000

27 22 0.0613000 -0.0400000

29 23 0.1024000 -0.0563000

30 24 0.1425000 -0.0700000

31 25 0.2017000 -0.0864000

32 26 0.2809000 -0.1019000

34 27 0.4416000 -0.1044000

35 28 0.5611000 -0.0783000

36 29 0.6803000 -0.0471000

37 30 0.8009000 -0.0198000

38 31 0.9194000 -0.0023000

39 32 1.1000000 -0.0001000

E-42
Appendix F

Integrated Coefficients from all Tests

Plots of Integrated Coefficients

F-l
Colorado State University Environmental Wind Tunnel Test Results

SERI S809 Airfoil

Reynolds Number = 650,000

alpa Cn Ct CI Cdp LFA Tunnel a Probe a

deg deg psi psi

-0.25 0.151 -0.002 0.151 0.002 0.808 0.047 0.047

1.75 0.354 0.01 0.354 0.001 4.09 0.048 0.048

3.81 0.56 0.035 0.561 0.002 7.62 0.048 0.048

5.92 0.762 0.073 0.765 0.006 10.9 0.049 0.049

7.94 0.854 0.104 0.86 0.015 13.8 0.05 0.05

9.98 0.841 0.116 0.848 0.031 16.4 0.049 0.048

11 0.884 0.128 0.892 0.043 17.4 0.049 0.049

12 0.879 0.136 0.888 0.049 18.4 0.049 0.048

13 0.918 0.145 0.927 0.043 19.7 0.049 0.049

14 0.901 0.148 0.91 0.075 20.8 0.051 0.051

15 0.914 0.148 0.91 0.075 20.8 0.051 . 0.051

16 0.922 0.153 0.928 0.107 22.9 0.049 0.049

17 0.737 -0.066 0.686 0.278 23.3 0.048 0.047

18 0.693 -0.065 0.639 0.276 24.1 0.048 0.047

19 0.634 -0.07 0.576 0.273 25 0.047 0.046

20 0.613 -0.07 0.552 0.275 26 0.048 0.046

22 0.673 -0.076 0.596 0.323 28.4 0.045 0.044

23.9 0.743 -0.075 0.649 0.37 31.2 I 0.046 0.044

26 0.794 -0.076 0.68 0.417 33.9 I 0.045 0.041

30 1.02 -0.073 0.851 0.576 39.3 0.045 0.041

35 1.28 -0.067 1.01 0.789 45.7 0.042 0.035

40 1.52 -0.064 1.12 1.03 51.5 0.039 0.029

45 1.64 -0.05 1.12 1.19 57 0.037 0.021

50 1.75 -0.032 1.1 1.36 59.1 0.035 0.012

55.3 1.92 -0.018 1.08 1.58

60.2 1.87 0.002 0.931 1.62

65.2 2.22 0.038 0.968 2

70.2 2.18 0.039 0.776 2.04

75.2 2.22 0.062 0.63 2.13

80.2 2.37 0.082 0.485 2.32

85.1 2.15 0.107 .0.289 2.14

90.2 2.27 0.116 0.109 2.27

F-2
Colorado State University Environmental Wind Tunnel Test Resul.ts.

SEAl S809 Airfoil .

.Reynolds Number =500,000

Smooth

. . -:. v'.: :.-,:: :.'

, " . ... .." .. _.. .. ... ..

: -:.,.,., : .

.. . .....

alpha Cn cr CI Cdp LFA

deg deg

-2.23 -0.06 -0.004 -0.06 0.006 -2.34

-0.161. 0.156 -0.005 0.156 0.004 0.8

1.84 0.369 0.005 0.369 0.006 4.13

3.88 0.571 0.031 0.571 0.008 7.44

5.89 0.752 0.068 0.755 0.009 10.5

7.89 0.854 0.101 0.86 0.017 13.7

8.95 0.88 0.115 0.887 0.024 14.5

9.91 0.862 0.115 0.869 0.035 15.7

10.9 0.86 0.126 0.868 0.039 16.9

12 0.885 0.138 0.894 0.048 17.9

12.9 0.928 0.15 0.938 0.061 19.1

14 0.919 0.153 0.929 0.074 20

14.9 0.9 0.151 0.908 0.08 21

16 0.906 0.15 0.912 0.106 22.5

17 0.705 -0.07 0.655 0.271 23

18 0.641 -0.07 0.588 0.265 23.6

19 0.646 -0.075 0.587 0.281 24.5

20 0.663 -0.076 0.597 0.299 25.7

22 0.681 -0.076 0.603 0.326 28

24 0.744 -0.079 0.647 0.375 30.5

26 0.798 -0.077 0.683 0.419 32.9

28.1 0.884 -0.075 0.745 0.482 36.3

30 0.994 -0.073 0.824 0.56 38

35 1.33 -0.063 1.05 0.817 39.6

40 1.54 -0.058 1;14 1.03 39.6

45 1.74 -0.046 1.2 1.26 39.6

50 1.77 -0.031 1.12 1.38 39.6

55 2.07 -0.014 1.17 1.7 39.6

60 2.16 0.002 1.08 1.87 39.6

65 2.19 0.012 0.94 1.98 39.6

70 2.35 0.056 0.857 2.19 39.6

74.9 2.27 0.078 0.666 2.17 39.6

79.9 2.26 0.076 0.472 2.21 39.6

84.8 2.34 0.146 0.356 2.32 39.6

89.9 2.09 0.139 0.142 2.09 39.6

F-3
.Colorado State University Environmental Wind·Tunnel Test Data •.·•.·· ······· . . .

.SERIS809 Airfoil

Reynolds Number = 30Q,OOO

Smooth

alpha Cn Ct CI Cdp LFA

deg deg

0 0.105 -0.0116 0.105 0.0117 1.13

1.99 0.308 0 0.307 0.0116 3.59

4.08 0.544 0.025 0.545 0.0139 8.42

6.11 0.745 0.066 0.748 0.0135 10.7

8.14 0.874 0.105 0.88 0.0198 14.6

10.2 0.87 0.119 0.878 0.036 16.9

11.2 0.862 0.129 0.87 0.0446 17.4

12.2 0.846 0.132 0.854 0.0496 17.9

13.1 0.868 0.139 0.877 0.0619 20.5

14.1 0.884 0.148 0.894 0.0731 21

15.2 0.882 0.15 0.891 0.0865 22.4

16.3 0.777 0.003 0.745 0.22 23

17.2 0.638 -0.062 0.591 0.248 23.3

18.1 0.645 -0.067 0.592 0.265 23.7

19.2 0.64 -0.073 0.58 0.279 24.5

20.2 0.67 -0.071 0.604 0.298 26

22.1 0.666 -o.on 0.588 0.323 28.2

26.2 0.782 -0.075 0.669 0.412 34.3

30.2 1.14 -0.071 0.946 0.633 39.2

35.2 1.3 -0.063 1.02 0.799 46.1

40.3 1.46 -0.051 1.08 0.983 51.8

45.2 1.79 -0.05 1.23 1.31 56.7

45.1 1.66 -0.054 1.13 1.21 56.2

50 1.94 -0.047 1.21 1.51 59.1

60 2.14 -0.019 1.05 1.86 59.1

69.9 2.41 -0.024 0.805 2.27 59.1

80 2.2 0.076 0.456 2.16 59.1

90 2.24 0.132 0.128 2.24 59.1

F-4
Colorado State University Environmental Wind Tunnel Test Data

SERIS809 Airfoil

Reynolds Number = 650,000

Wind Turbine Roughness (Very Rough, LE Wrap Around)

alpha Cn Ct CI Cdp · LFA Pdyn Ptp

deg deg psi psi

0 0.115 -0.009 0.115 0.009 0.956 0.044 0.044

1.8 0.291 -0.0001 0.291 0.009 3.8 0.045 0.046

3.98 0.483 0.022 0.483 0.012 7.52 0.046 0.046

6.01 0.603 0.043 0.604 0.02 10.6 0.046 0.046

8 0.672 0.058 0.674 0.036 13.1 0.045 0.046

10.1 0.696 0.075 " 0.699 0.047 15.7 0.046 0.046

11.1 0.724 0.082 0.726 0.059 17 0.047 0.047

12.2 0.709 0.08 0.71 0.071 17.9 0.047 0.047

13.1 0.681 0.063 0.6n 0.092 18.7 0.047 0.047

14.1 0.647 0.041 0.638 0.119 19.8 0.046 0.048

15.2 0.657 0.014 0.637 0.158 . 21 0.047 0.048

16.2 0.852 0.019 0.823 0.219 22.7 0.047 0.048

17.1 0.951 0.022 0.915 0.259 24 0.046 0.045

18.2 0.988 0.054 0.956 0.257 24.7 0.046 0.045

19.2 0.957 0.035 0.915 0.282 25.6 0.045 0.042

20.2 0.784 -0.048 0.719 0.316 26.5 0.045 0.045

22.2 ·0.774 -0.049 0.698 0.338 29.1 0.044 0.042

24.2 0.736 -0.076 0.639 0.371 31.1 0.044 0.044

F-5
(

l

Colorado State University Environmental Wind Tunnel Test Data

SERI S809 Airfoil

Reynolds Number =500,000

Very Rough LE Wrap Around

alpha Cn Ct CI Cdp LFA

deg deg

0.17 0.113 -0.009 0.113 0.009 0.983

2.12 0.288 0.0001 0.288 0.01 3.73

4.16 0.473 0.021 0.473 0.013 7.54

6.25 0.591 0.043 0.592 0.022 10.7

8.2 0.667 0.058 0.668 0.037 13.2

10.2 0.705 0.076 0.707 0.049 15.7

11.3 0.705 0.083 0.707 0.056 17

12.3 0.704 0.081 0.706 0.071 17.9

14.3 0.642 0.05 0.634 0.109 19.8

15.2 0.632 0.02 0.615 0.146 20.8

16.3 0.698 0.02 0.676 0.175 22.5

17.2 0.786 -0.012 0.747 0.245 23.8

18.2 o.n -0.045 0.717 0.283 25

19.2 0.726 -0.058 0.666 0.294 25.9

.s 20.3 0.723 -0.075 .0.653 0.321 27.1

22.2 0.676 -0.076 0.598 0.326 29.3

24.2 0.733 -0.078 0.636 0.372 30.9

F-6
c.

Colorado State University Environmental Wind Tunnel Tesf6at~ .:

SERI S809 Airfoil .:-t • . .

:Reynolds Number = 300,000 .....

Very Rough LE Wrap Around

alpha Cn Ct CI Cdp LFA

deg deg

-0.09 0.111 -0.007 0.111 0.007 0.905

1.87 0.295 0~003 0.295 0.006 3.42

3.96 0.472 0.019 0.473 0.013 9.01

6.04 0.618 0.047 0.62 0.017 11

7.98 0.696 0.061 0.698 0.036 13.6

10.1 0.715 0.08 0.718 0.046 15.9

. 11 0.733 0.086 0.736 0.056 17.4

12.1 0.75 0.091 0.753 0.068 18

13.1 0.739 0.088 0.74 0.081 18.8

14.1 0.76 0.088 0.758 0.099 20.1

15 0.719 0.068 0.712 0.121 21.7

16.1 0.636 -0.071 0.591 0.245 22.8

17.1 0.625 -0.065 0.578 0.247 23.8

18.1 0.639 -0.074 0.584 0.27 24.6

19.2 0.719 -0~05 0.662 0.283 25.5

20.1 0.668 -0.078 0.6 ' 0.305 26.6

22.2 0.685 -0.079 0.605 0.331 29.6.

24.2 0.771 -0.076 0.672 0.386 30.4

F-7



Appendix G

Pressure Distributions' for

Reynolds Number 650,000 Smooth

G-l








Appendix H

Pressure Distributions for Reynolds Number 650,000 Rough

H-l





Appendix I

Pressure Distributions for

Reynolds Number 500,000 Smooth

1-1









Appendix J

Pressure Distributions for Reynolds Number 500,000 Rough

J-l





Appendix K

Pressure Distributions for

Reynolds Number 300,000 Smooth

K-l







Appendix L

Pressure Distributions for Reynolds Number 300,000 Rough

L-l





Document Control Page 1. NREL Report No.

NRElII'P·2S7-46S5

2. NTIS Accession No.

·0893000012

3. Recipienfs Accession No.

4. Title and Subtitle

Combined Experiment Phase I-Final Report

7. Author(s)

C.P. Butterfield, W.P. Musial, D.A. Simms

9. Performing Organization Nameand Address

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden. CO 80401

12. Sponsoring Organization Name and Address

NatiowRenewableEner~~

1617 Cole Blvd.

Golden. CO 80401

15~ Supplementary Notes

16. Abstract (Umlt:200 words)

5. Publication Date

October 1992

6.

8. Performing Organization Rept. No.

NREUI'P-2S7-4655

10. ProJecVTaskIWork Unit No.

WE21.8101

11. Contract (0) or Grant(G) No.

(0)

(G)

13. Type of Report& PeriodCovered

Technical Report

14.

How does wind tmmel airfoil data differ from the airfoil performance on an operating horizontal axis wind turbine (HAWf)?

The National Renewable Energy laboratory has been conducting a comprehensive test program focused on answering this

question and understanding the basic fluid mechanics of rotating HAWf stall aerodynunics. The basic approach was to

instrument a wind turbine rotor, using an airfoil that was well documented by wind funnel tests, and measure operating pressure

distributions on the rotating blade. Based on the integrated values of the pressure data, airfoil perfonnance coefficients were

obtained, and comparisons were made between the rotating data and the wind tunnel data. Care was taken to minimize the

aerodynamicand geometric differences between the rotating and the wind tunnel models

This is the first of two reports describing the Combined Experiment Program and its results. This Phase I report covers

background information such as test setup and instrunlc'ntanon. It also includes wind tunnel test results androughness testing.

17. Document Analysis

8. Desaiptors

wind turbines; wind turbine experimentalrotor dynamics; wind turbine aerodynamic pressure measurements

b. Identifiers/Open-Ended Terms

c. UOCategories

261

18. Availability Statement

NationalTechnical InfonnationService

U.S. Department of Conunerce

5285 PortRoyal Road

Springfield, VA 22161

FormNo. 0069B (6-30-87)

19. No. of Pages

222

20. Price

A10