NASA / TMm2001-210820 AIAA-2001-1058

Design and Integration of a Rotor Alone

Nacelle for Acoustic Fan Testing

Tony D. Shook, Christopher E. Hughes, William K. Thompson,

Paul F. Tavernelli, and Cameron C. Cunningham

Glenn Research Center, Cleveland, Ohio

Ashwin Shah

Sest, Inc., Middleburg Heights, Ohio

Prepared for the

39th Aerospace Sciences Meeting and Exhibit

sponsored by the American Institute of Aeronautics and Astronautics

Reno, Nevada, January 8-11, 2001

National Aeronautics and

Space Administration

Glenn Research Center

April 2001
Acknowledgments

The authors would like to thank Vic Canacci, Jose Gonsalez, Larry Heidelberg, Tony Herrmann, Gerald Hill,

Gene Pinali, Paul Steve, and Sam Yunis for their significant efforts in making the design and integration

of RAN possible.

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Price Code: A03

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Price Code: A03

Available electronically at http://gltrs.grc.nasa.gov/GLTRS
DESIGN AND INTEGRATION OF A ROTOR ALONE NACELLE

FOR ACOUSTIC FAN TESTING

Tony D. Shook, Christopher E. Hughes, William K. Thompson,

Paul F. Tavemelli, and Cameron C. Cunningham

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Ashwin Shah

Sest, Inc.

Middleburg Heights, Ohio 44130

Abstract

A brief summary of the design, integration and

testing of a rotor alone nacelle (RAN) in NASA

Glenn's 9'x15' Low Speed Wind Tunnel (LSWT) is

presented. The purpose of the RAN system was to

provide an "acoustically clean" flow path within the

nacelle to isolate that portion of the total engine system

acoustic signature attributed to fan noise. The RAN

design accomplished this by removing the stators that

provided internal support to the nacelle. In its place,

two external struts mounted to a two-axis positioning

table located behind the tunnel wall provided the

support. Nacelle-mounted lasers and a closed-loop

control system provided the input to the table to

maintain nacelle to fan concentricity as thermal and

thrust loads displaced the strut-mounted fan. This

unique design required extensive analysis and

verification testing to ensure the safety of the fan

model, propulsion simulator drive rig, and facility,

along with experimental consistency of acoustic data

obtained while using the RAN system. Initial testing

was used to optimize the positioning system and

resulted in concentricity errors of+ 0.0031 inches in the

horizontal direction and +0.0035/--0.0013 inches in the

vertical direction. As a result of successful testing, the

RAN system will be transitioned into other acoustic

research programs at NASA Glenn Research Center.

Bacl_round

In recent years, NASA has aggressively

studied the noise characteristics of the fan bypass stage

in modem turbofan engines. The objective was to

better understand and thus mitigate aircrat_ engine noise

near airports. Previous wind tunnel testing identified

potential noise reduction concepts that contributed

significantly to the successful achievement of the

aggressive milestones in NASA's aircraft noise

reduction programs. However, further investigation of

the noise generating mechanisms in turbofan engines

was needed if additional noise reduction was to be

achieved. The knowledge gained would lend itself to

developing novel technologies targeted at specific noise

areas. As a result, an experimental program called the

Source Diagnostic Test (SDT) was initiated to

investigate these noise generating mechanisms

associated with turbofan engines in the area of fan

broadband noise. The investigation was carried out in

the acoustically treated NASA Glenn 9'x15' LSWT

using the Ultra High Bypass (UHB) fan drive rig

(Fig. 1), an air turbine driven propulsion simulator. The

test article was a 1/5-scale model of a current generation high-bypass turbofan engine.

The RAN project, part of the SDT test

program, called for the development of an "acoustically

clean" flow path within the nacelle. Specifically, the

internal exit guide vanes, stators, or mounting struts that

contributed to the engine system acoustic signature

needed to be removed. Previous acoustic research has

identified that a primary source of broadband noise in a

turbofan engine is the fan wake interacting with the

downstream stators. By removing this farffstator

interaction through elimination of the stators, the fanonly noise signature could be characterized, and the

NASAJTM--2001-210820 1
Fig.1. Turbofan Simulation Test in NASA Glenn

9'xl 5' LSWT in Standard Acoustic Configuration

interaction noise generating mechanism could be better

defined. However, for this engine model, the stators

provided the only nacelle support to the UHB drive rig.

The only means of achieving such an 'acoustically

clean' design was to decouple the nacelle from the

model centerbody. This required the nacelle to be

externally mounted, independent of the fan and UHB

drive rig.

The designers of the RAN system were faced

with significant challenges due to the acoustic research

requirements. The primary design challenge was to

maintain an "acoustically clean" environment by

providing external nacelle support that would not

contaminate the acoustic environment. The nacelle

support structure could not intrude into the model flow

path nor create any noise reflecting surfaces that the

acoustic microphones would record. In addition, the

support structure design could not create any noise

caused by air flowing over the structure.

Another major challenge facing the RAN

design team was the requirement to maintain tight

concentricity between the fan and nacelle during testing

to ensure circumferentially uniform fan tip clearance

and, uniform aerodynamic fan loading. The fan tip

clearance was anticipated to be 0.020 inches at

maximum fan testing speed of 12,746 RPM (100.7% of

corrected fan design speed). In addition, if the

concentricity offset exceeded 0.005 inches (indicating

that the system was not operating properly), all motion

of the RAN system would be stopped. An earlier

research study of fan model displacement, with a

traditional stator supported nacelle, found that the fan

face would pitch downward as much as 0.080 inches,

yaw to one side 0.040 inches, and move forward

0.125 inches, due to thermal loads in the model and

aerodynamic thrust loads introduced by the fan. During

normal operation of the UHB drive rig, these

displacements do not occur quickly since the fan speed

changes are made gradually.

The displacements due to thermal loads were

attributed mainly to heating gradients in the drive rig

especially near the drive turbine, which was located on

top of the drive strut and on the same shaft as the fan.

Air at 450 psi and 600°F was introduced to the drive

turbine through the floor into the strut and the turbine

plenum, causing high local heating. The oil for the

shaft bearings operates at a cooler 250°F, which kept

the internal drive rig temperatures at that level.

Additional thermal gradients arose from relatively low

turbine exit temperatures and the external convective

cooling of the entire test structure produced by the wind

tunnel and fan air flows over the drive rig. This

combination of sources and sinks generates large

thermal gradients that result in non-repeatable rig

deformations with fan speed. A passive displacement

system, one that would control the position of the

nacelle with respect to the fan, was deemed risky due to

the inconsistent rig displacements. Considering all

these factors, an active control system was necessary.

for RAN based on the positioning requirements during

testing.

System Description

As stated earlier, the design goal of RAN was

to operate at a fan speed of 12,746 corrected rpm while

maintaining concentricity within 0.005 inches and a fan

tip clearance with the nacelle of 0.020 inches. A twostrut configuration was selected to support the nacelle

externally, extending horizontally from the nacelle to

the test section wall (Fig. 2). A nacelle support system

with two thin struts was selected over a single thick

strut of equal rigidity to help minimize the acoustic

disturbance of the support. In addition, the struts were

positioned on the opposite side of the nacelle with

respect to the acoustic microphones, so that they were

in the "shadow" of the nacelle and therefore

acoustically invisible. To further reduce any chance of

acoustic impact, aerodynamic leading and trailing edges

were added to the struts (Fig. 3). These struts also

provided an ideal means for routing hundreds of

instrumentation, electric and cooling lines to the model.

The positioning table was mounted outside the

tunnel wall to minimize the flow field disturbances

(Figs. 2 and l 1). The positioning table provided

movement in both the horizontal and vertical directions.

Position correction in the axial direction was not

required since the outer flow path around the fan was

NASA/TM--2001-210820 2
FRONT VIEW

FmModelCenterbody

Drh, e Rig Support strut

TOP VIEW

Air Turb_m¢ Drive Rig

_rms (2)

Fig. 2. Front and Top View of RAN Configuration

for 9' x 15' LSWT

were selected to maximize stiffness. A five horsepower

servomotor with a 100:1 gearbox drives a zero

backlash, preloaded, ball screw on each axis. Four

electric brakes, one on each ball screw shaft and one

integral to each servomotor, were used to hold table

position. Table 1 provides a summary of the RAN

position control system specifics, and Fig. 4 shows the

two-axis positioning table.

The feedback control system was designed for

precision, redundancy, and low cost. Four laser sensors

(Figs, 5, 6 and 7), mounted on the nacelle at 90-degree

intervals, measured the distance from the nacelle to the

center body. Two of the laser sensors, one on each

axis, provide the primary feedback signals for the

Specification Characteristics

Drive motors Five horsepower servomotor

Drive control Servo drives

Gear mechanism Right angle 100:1 gearhead

Drive mechanism 1%" alia. x .50 lead rolled ball screw (both axes)

Rail system Linear ball bearings with rails (both axes)

Mechanical Mechanical end-of-travel limit switches

limits Adjustable hardstops

Brakes: Fail-safe (energized to release brakes)

Ball Screw Shaft- 24 VDC (both axes)

Servomotor- 18VDC (both axes)

Rated speed 0.01 in./sec

Allowable travel 2 in. (both axes)

Repeatability 0.0002 in. (both axes)

Position accuracy 0.0002 in./inch of travel (both axes)

Table 1. RAN Positioning Table Specifications

Flow Y' x 5" x I/4"

Steel Tube

---_ Instrumentation

& Cabling

Fig. 3. Cross-section of Nacelle Support Strut

(Section A-A from Fig. 2)

nearly constant in diameter, and therefore, any fan

motion in this direction would not impact concentricity

or tip clearance. The positioning table design was

optimized for rigidity (2" thick steel plate construction),

accuracy (0.0002"/inch of travel), and repeatability

(0.0002"). Each table rode on bearings and rails that Fig. 4. Two-axis Positioning Table

NASA/TM--2001-210820 3
positioning table control system; the other two laser

sensors were independent backups. The system was

later modified during testing by averaging the laser

sensor signals to allow more accurate positioning of the

nacelle and reduce the positioning deadband, l Space

constraints dictated that the lasers could not be mounted

with the beams directed radial; consequently, both the

source and scatter signals were deflected 90 ° via

polished aluminum mirrors (Fig. 5). Bench tests

confirmed the validity of this approach. One inch

diameter flats were machined on the centerbody as

targets and were located 6.31" from their respective

mirror. Each laser sensor was enclosed in a sheet metal

housing that directed a cooling gas to maintain the laser

temperature below the manufacturer's limit of 120°F;

beyond this the measurement drift would lead to

unacceptable position errors. The analog signals from

the laser sensors were fed into a multi-purpose I/O card,

as were the discrete signals for each laser sensor alarm,

motor thermostats, axis faults and axis motion

indicators. Discrete outputs from this card enabled

motion and placed the servo drives in manual or

automatic mode.

Fig. 8 shows the flowchart for the control

system. The positioning table control system consisted

of two servomotors, one for each axis, and their

controllers. The servomotor controllers executed

motion commands, tracked table position and

controlled motor/shaft brakes. The controllers

maintained serial communication with a STD-bus based

microcomputer. The microcomputer sampled the laser

sensor signals, computed the position correction

required to achieve concentricity, and commanded the

servomotor controllers to move the table accordingly.

The graphical user interface allowed an

operator to monitor and, if needed, operate the RAN

system during test activities (Fig. 9). The operator

could manually move the table, activate/deactivate

automatic control, monitor table position and nacelle

concentricity, and "zero" table/laser positions, as well

as diagnose and respond to fault conditions.

A combination of parameter constraints in the

software, limit switches, and hard stops ensured that the

concentricity error could not reach the point where the

fan blades would come into metal-to-metal contact with

the nacelle. In addition to the software and hardware

safety features, a 0.67 inch thick, low-density,

polyurethane foam, abradable, material was used as a

rub strip over the fan blades. Based on the anticipated

fan/drive rig displacement and fan tip gap during

normal testing, the clearance stack-up showed a safety

factor greater than 10.

Laser Mirror Laser Sensor

Nacelle Jy

Target /

Centerbody

Fig. 5. Laser Displacement Sensor

Schematic

\

Cooling Ll_

.... .._:

Fig. 6. Laser Displacement Sensor in RAN Assembly

(w/Thermal Housing Removed)

Fig. 7. Internal View of Flowpath,

Aft Looking Forward

NASA/TM--2001-210820 4
RAN POSITIONING TABLE CONTROL SYSTEM

I_:,AS_E,L___LE,=_::_,_= A-_ ,=_A,LE', _,,_;o_ _ ,_ b_p_

Fig 8. Control System Flowchart

Fig. 9. Positioning Table Operator Control Interface

Analysis and Verification

An extensive analysis and verification effort

was undertaken to ensure that the RAN system was

structurally, dynamically and aeroelastically safe. As

described earlier, the hardware was designed to accept

significant incursions of the fan tips into the rub strip

without damage to the fan or the rest of the model

hardware. The drive rig in the 9'x15' LSWT utilized

an automatic shutdown capability which was triggered

whenever a facility-critical parameter, such as bearing

temperature, vibration, etc., exceeded its limits. As the

thrust load from the fan relieved, the drive rig would

quickly displace back toward its static position.

Because the positioning system was not designed to

control for rapid displacements, a significant fan

incursion into the rub strip was possible, and

stabilizing/containing such a violent event was a critical

design consideration. Consequently, low-density

polyurethane foam was selected for the rub strip

material. An analytical model was developed to verify

the rub stability for a range of rub strip material

densities (10 to 40 lb/fi3). A test apparatus and

procedure was also developed to validate properties of

the material used in the rub stability analysis.

Because the fan and nacelle were decoupled,

each was subject to a range of dynamic and steady

loads that would result in relative motion between two.

Due to the independent motion of the fan blades and the

nacelle, it was possible that a rub against the nacelle

could cause instabilities in their relative motion. The

resulting "fan bounce" could cause damage to the fan

and/or unsafe conditions in the wind tunnel. Since the

clearance between the fan blade tips and the rub strip

was anticipated to be 0.020", the entire system had to

be designed and analyzed very prudently. Due to the

random characteristics of loads on the test structure, a

probabilistic analysis of the loss of clearance was

deemed necessary.

The objective of the probabilistic analysis was

to analyze/design the RAN system such that the

probability of exceeding the design clearance

requirement of 0.020" was minimal and the margin of

safety acceptable. The entire analysis/design effort

was divided into the following four main parts:

(1) preparation of a detailed finite element model, as

shown in Fig. 10; (2) developing a methodology to

quantify the probability of exceeding the design

clearance; (3) verification of the methodology; and

(4) computing the probability of exceeding the

clearance for the actual RAN system.

z

1

x _ Roller Al_JrleNacelle

y_

RAN SL4_I_:Irl 5¥slefrt Ft'rdleElen_ent M,',del

Fig. 10. Finite Element Model of the RAN System

(Fan and Drive Rig not Shown)

NASA/TM--2001-210820 5
Thefinite element model included the nacelle,

struts, fan drive rig, the connections between nacelle

and struts, the positioning table, the connections

between the positioning table and struts, and

the positioning table bearings. A probabilistic

methodology was developed and consisted of:

(1) computing the frequency domain random loads

(power spectral density [PSD] functions), (2) performing the random vibration analysis, (3) quantification of

the probability of loss of clearance using barrier

crossing analysis.: To verify the methodology, a single

strut typical of the design used in the RAN system was

mounted to the tunnel wall without a nacelle and fan to

determine the flow induced vibrations and its dynamic

response. The methodology was applied to a finite

element model of the strut and the computed dynamic

characteristics were compared with those from the tests.

The experimentally extracted damping was used in the

analysis. A comparison of the free vibration analysis

results with the test data (Table 2) shows excellent

correlation. The mode shape correlation is given in

Table 3, and is considered good when the diagonal

terms are between 0.9 and 1.0 and the off-diagonal

terms are between 0.0 and 0.1. The first two modes are

all in or near these ranges. However, the correlation for

the third mode (torsional) and its related off-diagonal

terms are not as close as expected, mainly due to

insufficient instrumentation required to capture the

torsional effect. The torsional mode was not expected

to contribute significantly to the loss of clearance due to

its high frequency; it was computed mainly to verify

that the first two modes of vibration contained 99% of

the energy. To provide further confidence in the model,

the computed accelerations of the struts at different

locations were compared with those from the test data.

The experimental and analytical results, as well as their

trends, compared well, which provided confidence in

the methodology used. A full report of the comparison

of this acceleration data has been omitted for brevity.

Mode Test Correlated Analysis Description

Frequency Frequency Frequency

(Hz) (IDEAS) (Nastran)

1 19.92 20.11 19.48 Out-of-plane bending

2 60.44 57.54 56.3 In-plane bending

3 135.0 133.2 131.0 2 '_ Out-of-plane

Table 2. Dynamic Frequency Correlation for Struts

The experimentally verified strut design, as

described above, was used in the RAN support system.

Random loads, determined from hot-wire anemometer

data taken on a previous model turbofan simulation test

in the 9'x15' LSWT under a steady-state flowfield at

Mach 0.1 and atmospheric pressure, were converted

into the PSD functions using IDEAS computer code. A

random vibration analysis of the RAN system was

performed using MSC/NASTRAN computer code. 3

Table 4 shows the first five free vibration modes with

the main component reacting in parenthesis.

Test Modes Analytical Modes

1 2 3

1 0.90 0.07 0.41

2 0.04 0.98 0.03

3 0.12 0.05 0.83

Table 3. Structural Dynamic Modal Correlation

Mode Description Frequency

1 Beam Bending (struts) 25.4 Hz

2 Chordwise Bending (struts) 43.6 Hz

3 Beam Torsion (struts) 73.2 Hz

4 Plate Bending (table) 83.2 Hz

5 Plate Torsion (table) 86.7 Hz

Table 4. Principle Modes of System Vibration

The root mean square loss of clearance, as

well as the auto correlation functions at different

locations around the periphery of the nacelle, were

computed. These results were used in the barrier

crossing analysis to quantify the probability of

exceeding the loss of clearance. The analysis showed

that the likelihood of losing the 0.020 inch clearance

during a typical two hour test was 62 out of 100,000.

Divergence and flutter analysis of the RAN

system was performed to verify the stability under

aeroelastic conditions at Mach 0.2. Although the test

condition would not exceed 0.1 Mach, the stability

verification up to 0.2 Mach provided additional margin

of safety. Aerodynamic analyses based on both the

Double-Lattice Subsonic Lifting surface and VortexLattice theory revealed that the system does not diverge

up to 0.2 Mach. 4 The flutter analysis using the PK

method showed that the system has enough structural

and aerodynamic damping to absorb the aerodynamic

loads up to 181 Hz vibration frequencies and shows no

sign of flutter. 5 Since the system was not expected to

respond beyond 181 Hz frequencies, the flutter analysis

for higher modes was deemed unnecessary. Thus, the

RAN support system was found to be stable with regard

to divergence and flutter up to Math 0.2.

NASAJTM--2001-210820 6
Hardware Checkout and Installation

Prior to installation in the 9'x 15' LSWT, a

comprehensive checkout of RAN positioning system

was completed. The RAN traverse table was floormounted and qualified with the same hardware that

would be used in the wind tunnel (Fig. 11). The target

centerbody (w/machined fiats) was mounted to a

controllable two-axis traverse system (Probe Actuator

Control System, or PACS) that provided motion with a

resolution of 0.001 inches, allowing the RAN system

response to be compared against known inputs. Checks

included manual and automatic operability, sampling

rate, vibrational response, and failure modes. Since the

main design goals of the RAN system was to prevent a

fan rub into the casing, the checkout was conducted

with verification of fail-safe operation as the principle

objective. However, this checkout could not simulate

the operating temperatures, excitation, facility noise,

and aerodynamic effects found in the LSWT; followon verification testing was needed. At this point, the

RAN system was ready for tunnel installation.

Modifications to the wind tunnel were required

to support the positioning table and maintain the

acoustic environment of the tunnel test section. By

mounting the positioning table behind the tunnel wall,

the table and its support structure caused negligible

changes to the acoustic environment. The tunnel wall

that supports the positioning table was stiffened with

additional beams (Fig. 12). A platform was constructed

to support the positioning table, and was secured to

both the tunnel sidewall structure and ground for

maximum rigidity. Accurate alignment of the nacelle

with the drive rig fan was critical for this test. Proper

flow-fields would not be created if the position of the

nacelle and fan drive rig were not accurately

maintained. The axial location of the positioning table

was set to a reference surface on the drive rig, while

horizontal and vertical alignment was obtained by

shimming the positioning table. Final concentricity of

the fan and the nacelle was achieved by "jogging" the

two-axis positioning table. New acoustic boxes were

fabricated to accommodate the positioning table and

support struts (Figs. 12 and 13). These acoustic boxes

maintained a uniform aeroacoustic environment around

the new RAN support hardware.

Integrated System Performance

During initial testing, the excitation level of

the nacelle was closely monitored, but never exceeded

the noise floor of the accelerometers. A post-run

impact test confirmed that the RAN system was highly

damped. On the first 100% speed test, a fan rub of

about 0.020 inches occurred. An alternate

configuration using a fixed nacelle supported by stators

was used to measure fan tip clearance. This test data

Fig. 11. Checkout of RAN w/PACS Traverse

Fig. 12. Wind Tunnel Modifications for RAN

Installation

Fig. 13. Front View of RAN Hardware in LSWT

NASA/TM--2001-210820 7
revealedclearanceof 0.004 inches at the fan leading

edge, not 0.020 inches as originally predicted.

Consequently, modifications were needed to improve

centering performance and decrease the positioning

deadband.

Thermal drift in the laser sensor readings was

the major contributor to displacement error; therefore, a

three-pronged approach was utilized to counteract drift.

First, the laser cooling system was improved by

increasing the coolant flow rate and chilling the coolant

fluid, lowering the temperature at the laser head by

approximately 30°F. Second, the amount of error

introduced by the thermal drift effect was calculated

from opposing lasers and subtracted from the control

readings. Third, startup and centering procedures were

developed to reduce relative drift. In addition,

instrumentation filters and improved averaging

provided excellent noise immunity.

The performance gains from optimization

were significant enough to reduce the deadband to

0.0015 inches. Analysis revealed concentricity errors

in the horizontal direction and vertical direction of

0.0032 inches and 0.0036/-0.0014 inches, respectively.

A full description of the optimization of RAN, along

with the concentricity analysis, can be found in Ref. 1.

Table 5 summarizes the characteristics of RAN before

and after optimization.

a result, extremely tight tip clearances can be

maintained for moderate ramp rates of fan speed.

The RAN system met or exceeded all design

requirements and verified the feasibility of independent

fan and nacelle testing. Baseline testing showed no

appreciable increase in broadband noise due to the

RAN hardware and tunnel modifications.

Aerodynamically, the uniformity of the flow path

generated by the RAN system allowed the researchers

to gather dynamic pressure data with confidence in its

quality. The robust mechanical design of the RAN

system proved to be structurally rigid, vibrationally

benign, and aeroelastically stable. The RAN system

displayed excellent reliability and consistency

throughout the program, and was deemed acoustically,

aerodynamically, and mechanically successful.

The successes of the RAN project will enable

its application in future NASA research programs.

Recently, a design was completed that integrates a third

axis that corrects for axial displacement of the fan and

drive rig. Future testing using the RAN system will

also include improvements to the laser sensor thermal

control system to reduce the sensor positioning error

due to thermal loads. In addition, a data recording

system will be installed to log laser sensor outputs and

sensor operating temperatures at both steady and

transient operating speeds.

Characteristic Final Initial

Resolution of Motion 0.0001 in. 0.0001 in.

Sampling Rate 1 Hz 2 Hz

Deadband 0.0015 in. 0.0040 in.

Total Runs (all speeds) 25 1

Total Run Time >S0 hours 1 hour

Runs w/no robs @100% Nc 14 0

Concentricity Error (Horiz) + 0.0032 in. --, + 0.025 in.

Concentricity Error (Vert) +0.0036/-0.0014 in. _, + 0.025 in.

Table 5. RAN Performance Summary

Conclusions

The Rotor Alone Nacelle (RAN) system was a

unique design that allowed the acoustic testing of an

isolated fan within the nacelle of a modem turbofan

model in the NASA Glenn 9'x15' Low Speed Wind

Tunnel. Prior characterization of the fan and drive rig

motion showed that displacement was not predictable

enough to exclude an active nacelle positioning control

system; the data from the RAN project strongly

supported this finding. The RAN system can maintain

relative position of a decoupled nacelle with respect to

an operating fan with high accuracy and precision. As

References

1. Cunningham, C.C., Thompson, W.IC, and Hughes,

C.E., "Performance Optimization of a Rotor Alone Nacelle

for Acoustic Fan Testing", ALgA 2001-0164, Jan. 2001.

2. Newland, D.E., "An Introduction to Random Vibration

and Spectral Analysis", Longman Group Limited, London.

3. MSC/NASTRAN User's Guide, Version 69, The

MacNeal-Scwendler Corporation.

4. Albano, E., and Rodden, W.P., "A Double-Lattice

Method for Calculating Lift Distributions on Oscillating

Surfaces in Subsonic Flows", AIAA Journal, Feb. 1969,

Vol. 7, No. 2, pp. 279-285.

5. "Modal Flutter Analysis Study; Vol. IV, Aero-ServoElastic Stability Analysis Program: PASES", Report No.

SDI5204R, Hughes Aircraft Co.

NASA/TM--2001-210820 8

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

April 2001 Technical Memorandum

4. TITLE AND SUI_]ilLE

Design and Integration of a Rotor Alone Nacelle for Acoustic Fan Testing

6. AUTHOR(S)

Tony D. Shook, Christopher E. Hughes, William K. Thompson,

Paul F. Tavernelli, Cameron C. Cunningham, and Ashwin Shah

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

5. FUNDING NUMBERS

WU-781-13-01-00

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-12738

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--2001-210820

AIAA-2001-1058

11. SUPPLEMENTARY NOTES

Prepared for the 39th Aerospace Sciences Meeting and Exhibit sponsored by the American Institute of Aeronautics and

Astronautics, Reno, Nevada, January 8-11, 2001. Tony D. Shook, Christopher E. Hughes, William K. Thompson,

Paul F. Tavernelli, and Cameron C. Cunningham, NASA Glenn Research Center; and Ashwin Shah, Sest, Inc.,

Middleburg Heights, Ohio 44130. Responsible person, Tony D. Shook, organization code 7725, 216--433-6373.

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Subject Categories: 07, 09, 33, and 37 Distribution: Nonstandard

Available electronically at htm://_ltrs._c.nasa.eov/GLTRS

This publication is available from the NASA Center for AeroSpace Information, 301--621-0390.

13. ABSTRACT (Maximum 200 words)

A brief summary of the design, integration and testing of a rotor alone nacelle (RAN) in NASA Glenn's 9'x15' Low Speed

Wind Tunnel (LSWT) is presented. The purpose of the RAN system was to provide an "acoustically clean" flow path

within the nacelle to isolate that portion of the total engine system acoustic signature attributed to fan noise. The RAN

design accomplished this by removing the stators that provided intemal support to the nacelle. In its place, two external

struts mounted to a two-axis positioning table located behind the tunnel wall provided the support. Nacelle-mounted lasers

and a closed-loop control system provided the input to the table to maintain nacelle to fan concentricity as thermal and

thrust loads displaced the strut-mounted fan. This unique design required extensive analysis and verification testing to

ensure the safety of the fan model, propulsion simulator drive rig, and facility, along with experimental consistency of

acoustic data obtained while using the RAN system. Initial testing was used to optimize the positioning system and resulted

in concentricity errors of_+0.0031 in. in the horizontal direction and +0.0035/-0.0013 in. in the vertical direction. As a

result of successful testing, the RAN system will be transitioned into other acoustic research programs at NASA Glenn

Research Center.

14. SUBJECT TERMS

Rotor blades; Turbomachinery; Fan; Wind tunnel models;

Active control; Nacelles; Acoustics

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION

OF REPORT OF THIS PAGE

Unclassified Unclassified

NSN 7540-01-280-5500

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

15. NUMBER OF PAGES

14

16. PRICE CODE

AO_

20. LIMITATION OF ABSTRACT

Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102