NASA/TM-2000-210311

Development of a Large Field of View

Shadowgraph System for a 16 Ft. Transonic

Wind Tunnel

Michael A. Talley, Stephen B. Jones, and Wesley L. Goodman

Langley Research Center, Hampton, Virginia

September 2000

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NASA/TM-2000-210311

Development of a Large Field of View

Shadowgraph System for a 16 Ft. Transonic

Wind Tunnel

Michael A. Talley, Stephen B. Jones, and Wesley L. Goodman

Langley Research Center, Hampton, Virginia

National Aeronautics and

Space Administration

Langley Research Center

Hampton, Virginia 23681-2199

September 2000
Available from:

NASA Center for AeroSpace Information (CASI)

7121 Standard Drive

Hanover, MD 21076-1320

(301) 621-0390

National Technical Information Service (NTIS)

5285 Port Royal Road

Springfield, VA 22161-2171

(703) 605-6000
Contents

Page

ABSTRACT .................................................................. 1

INTRODUCTION ............................................................. 1

ANALYSIS .................................................................. 1

Features Needed ......................................................... 1

Constraints on the Shadowgraph System ...................................... 1

DESCRIPTION OF SHADOWGRAPH SYSTEM .................................... 2

TESTS & RESULTS ........................................................... 8

Lab Tests .............................................................. 8

Tests to Assess Background Subtraction Technique ............................. 9

Aerodynamic Tests in the 16 ft. TT ......................................... 11

CONCLUSIONS ............................................................. 19

REFERENCES .............................................................. 19
List of Figures

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Page

1. Shadowgraph configuration at 16 ft. TT .................................... 2

2. Optical Layout of shadowgraph system at 16 ft. TT ........................... 3

3. Layout of light source and camera ......................................... 3

4. Digital shadowgraph system ............................................. 4

5. 30 frame pers second video system ........................................ 4

6. Control room image acquisition station ..................................... 5

7. Rear view of cameras and light sources looking into test section ................. 6

8. High resolution digital camera and light source setup .......................... 7

9. Digital image of flow from heat gun using a 4 ft. X 4 ft. Reflexite screen .......... 8

10. Heat gun flow after background subtraction ................................ 9

11. Test section horizontal wall displacement versus temperature ................. 10

12. Location of cover plates and plenums on Laser turret ........................ 11

13. Baseline configuration at Mach=0.78, Alpha=5.2 deg, and Beta=3.0 deg (Point 69).

..................................................................... 3

14. Baseline configuration at Mach=0.78, Alpha=5.2 deg, and Beta=3.0 deg (Point 69)

with sequence average subtracted ........................................... 14

15. 15% Porous plate configuration with plenum at 0.25 inches. Mach=0.76, Alpha=5.2

deg, Beta=0.0 deg (point 108) .............................................. 15

16. Sequence average subtracted from image of 15% Porous plate configuration with

plenum at 0.25 inches. Mach=0.76, Alpha=5.2 deg, Beta=0.0 deg (point 108) ....... 16

17. Porous plate configuration with 1Ainch deep plenum cavity. Mach=0.74, Alpha=4.0

deg, Beta=0.0 deg (point 688) .............................................. 17

18. Sequence average subtracted from image of porous plate configuration with 1Ainch

deep plenum cavity. Mach=0.74, Alpha=4.0 deg, Beta=0.0 deg (point 688) ......... 18

ii
ABSTRACT

A largefield of view shadowgraphflow visualizationsystemfor theLangley16ft.

TransonicTunnel(16fl.TT) hasbeendevelopedto providefast,low cost,aerodynamicdesign

conceptevaluationcapabilityto supportthedevelopmentof thenextgenerationof commercial

andmilitary aircraftandspacelaunchvehicles.Key featuresof the 16ft. TT shadowgraph

systemare:1)highresolution(1280X 1024) digital snap shots and sequences; 2) video recording

of shadowgraph at 30 frames per second; 3) pan, tilt, & zoom to find and observe flow features;

4) one microsecond flash for freeze frame images; 5) large field of view approximately 12' X 6';

and 6) a low maintenance, high signal/noise ratio, retro-reflective screen to allow shadowgraph

imaging while test section lights are on.

1.0 INTRODUCTION

This paper discusses the development of a large field of view shadowgraph flow

visualization system for the Langley 16 ft. Transonic Tunnel (16 fl.TT). Topics discussed

include: needs analysis; description of the shadowgraph system; and tests & results.

This work was funded by the Wind Tunnel Enterprise primarily to provide fast, low cost,

aerodynamic design concept evaluation capability to support the development of the next

generation of commercial and military aircraft and space launch vehicles. This may include

research and development with passive porosity, synthetic jets, blowing, integrated

sensor/actuator/controller surfaces, designer materials for noise control, and other techniques

where novel control approaches are used.

2.0 NEEDS ANALYSIS

2.1 Features Needed

The main features desired by users are visualization of flow structure and spatial

distribution of flow features within a field of view up to 9 ft. wide by 5 ft. high. To obtain

adequate detail for a field of view this large, high resolution and high contrast images will be

needed. Additional desired features include: a) ability to take digital snap shots and sequences

and continuously record video to VHS tape from the 16 ft.TT control room; b) ability to include

test parameters with images such as test title, time & date, Mach number, temperature, dynamic

pressure, etc.; c) non-intrusive to the flow; d) cost effectiveness; e) little or no impact on

productivity, f) easy maintenance; and g) ability to accommodate other test techniques.

2.2 Constraints on the Shadowgraph System

The shadowgraph cameras and light source packages must be installed outside of the test

section plenum to avoid excessive vibrations and temperatures that occur while the tunnel is

running. Optical access must be through the plenum and test section windows. A low

maintenance, high signal/noise ratio retro-reflective screen will need to be applied to the far side
testsectionwall approximately30ft. from thecamera.A field of view of approximately9 ft. by

5 ft. atthe centerof thetestsectionwill requirethescreento be 12ft. wideby 6.5ft. high. The

computerusedfor digital imageacquisition,VHS taperecorder,andall systemcontrolsmustbe

locatedin thecontrolroom. A genericshadowgraphconfigurationthatmeetstheseconstraintsis

shownin Figure 1.

ital Image Acquisition

Using Computer & Frame Grabber

Shadowgraph

Camera &

Light Source /

Plenum

Window

Figure 1.

Test Section 12' X 6.5' RetroWindow Reflective Screen

Shadowgraph configuration at 16 ft. TT.

4.0 DESCRIPTION OF SHADOWGRAPH SYSTEM

Key features of the 16 ft. TT shadowgraph system are: 1)high resolution (1280 X 1024)

digital snap shots and sequences1; 2) video recording of shadowgraph at 30 frames per second; 3)

pan, tilt, & zoom for scanning flow features; 4) one microsecond flash 2 for freeze frame images;
5) large field of view approximately 12' X 6'; and 6) a low maintenance, high signal/noise ratio,

retro-reflective 3 screen to allow shadowgraph imaging while test section lights are on. The

optical layout of the system is shown in Figure 2 and the layout of the light source and camera is

shown in Figure 3.

Plenum

Window I_

Test Section

Window

Model--

Retro-Reflective

Screen

Shadowgraph

System on

Mezzanine

16

30'

Optical Layout of shadowgraph system at 16 ft. TT.

:1

Digital Camera OrCCD Video Camera

Camera Lens 50-5Q

(Fixed or Zoom) Beamsplitter

Figure 3. Layout of light source and camera.
Block diagrams showing components of the digital and 30 frame per second video

systems are shown in Figure 4 and Figure 5 respectively.

Tunnel Control Room

Monitor

1

Windows Computer

Network

Connection

Tunnel Mezzanine

Flash Trigger

(50 Ohm Coax )

Fiber Optic Interface Cables

(100 M ete rs)

._ Cooke SensiCarn

Digital Camera

Figure 4. Digital shadowgraph system.

Tunnel Control Room

Video Monitor

[

S-VHS VCR

Tunnel Mezzanine

Figure 5.

(50 Ohm Coax )

Video Camera

Video (50 Ohm Coax)

30 frame pers second video system.

4
A pictureof theimageacquisitionstationin thecontrolroomis shownin Figure 6.

Figure 6. Control room image acquisition station.

A rear view of the camera and light source setups looking through the plenum and test

section windows is shown in Figure 7. A close-up picture of the high resolution digital camera

and light source setup is shown in Figure 8.
Figure 7. Rear view of cameras and light sources looking into test section.
Figure 8. High resolution digital camera and light source setup.
5.0TESTS& RESULTS

5.1LabTests

Thedigital andvideoshadowgraphsystemsweretestedin thelabusingacompletemockupof the 16ft. TT opticallayout. Figure 9 showsa shadowgraphimageof flow from aheatgun

acquiredfrom thedigital cameraat aresolutionof 1280X 1024. Theheatgunwas22ft. from

thecameraandthereflexite screenwas30ft away. Thefield of view was50in. high

correspondingto animageresolutionjust under0.05in. perpixel.

Figure 9. Digital imageof flow from heatgunusinga4 ft. X 4 ft. Reflexitescreen.

Figure 9 wasenhancedby subtractingabackgroundimagein whichtheheatgunwas

removed.Theresultis thatmoreflow detailcanbe seenasshownin Figure 10. This
Figure 10. Heatgun flow afterbackgroundsubtraction.

enhancementtechniqueprovidessignificantimprovement,however,thelocationof theretroreflectivescreenmuststayfixedrelativeto the shadowgraphcamera.

5.2TeststoAssessBackgroundSubtractionTechnique

Backgroundsubtractionwasnotpossibleduerelativedisplacementof thetest section

wall with respectto theshadowgraphcameralocation.Horizontalrelativedisplacementsof 3

targets(X1,X2, andX3) onthetestsectionwall weremeasuredfrom theshadowgraphcamera

locationusingvideophotogrammetry.Over700data pointsweretakenoveranoperational

rangeofMach 0to Mach1.2wherethetunnelairtemperaturerangedfrom 65Fto 170F. The

displacementfor eachtargetat eachdatapoint is plottedwith respectto theairtemperatureas

shownin Figure 11. Measuredverticaldisplacementswereinsignificant.
Test Section Horizontal Wall Displacement VS Air Temperature

0.4

m

E

¢J

_m

O.

01

_3

0.35

0.25

0.15

0.05

_.--.--_Xl data

: X2 data

t X3 data

_Linear (X2 data) y = 0.0029x - 0.1924

i

80 1O0 120 140 160 180

Temperature, F

Figure 11. Test section horizontal wall displacement versus temperature.

10
5.3AerodynamicTestsin the 16ft. TT

Useof shadowgraphmeasurementtechniqueduringBoeingAirborneLaserTest534at

16ft. TransonicTunnelmadeit possibleto successfullyevaluateflow controlimprovementsin

anattemptto eliminateunsteadyshocksonalaserturret. Thiswaspossibledueto the

visualizationof flow featuresassociatedwith differentaerodynamicconfigurationsof thelaser

turretcoverplates.Figure 12showsthelaserturretandlocationof coverplates. Testresults

from threeplateconfigurationswhich demonstratedifferentflow featureshavebeenselectedfor

discussion.Theseare: thebaselineplates;plateswith 15%porosityand1/4in.plenumdepth;

andplateswith 25%porosityand 1/2in. plenumdepth. The25%porosityplateswerepartially

coveredwith Patch1asshownin thefigure.

Typical Dynamic Pressure Tap

Porous or Solid Plate

/ \

Plenum T

Typical Steady State Pressure Tap

Figure 12. Location of cover plates and plenums on Laser turret.

As an alternate means of enhancement, an average of a sequence of 10 images for each

data point was subtracted from a single image. This provided enhancement of the dynamic

features in the flow. Table 1 summarizes the 3 configurations, notable flow features associated

with each configuration, and the corresponding figures that show the features.

11
Table1

TurretPlate Test Notableflow features ImagesShowing

Configuration Conditions Features

Baseline- no

porosity

15%Porosity

with 1/4in.

Plenum

25%Porosity

(Patch1)with

1/2in. Plenum

Mach=0.78

Alpha=5.2

Beta=3.0

Mach=0.76

Alpha=5.2

Beta=0.0

Mach=0.74

Alpha=4.0

Beta=0.0

Unsteadylambdashockfollowed

byrecirculatingturbulentflow

belowalow anglefreeshearlayer

Recirculatingturbulentflow below

ahighanglefreeshearlayer- no

lambdashockformation

Significantvortexformation&

burstingbelowthefreeshearlayer

Figure 13 & Figure 14

Figure 15 & Figure 16

Figure 17 & Figure 18

Size and location constraints limited the number and spacing of dynamic and steady state

pressure transducers on the turret. Without continuous or close spacing of pressure taps, both onand off-body, the presence of flow phenomena such as small lambda shocks, vortices, and high

angle shear layers would have to be inferred. The availability of the shadowgraph images

depicting ongoing global flow phenomena provided immediate insight into flow phenomena

affecting local pressure responses.

The continuous real time information in the shadowgraph images provided the observer

the ability to immediately determine which configurations: 1) eliminated the unsteady shocks; 2)

generated unwanted vortices; and 3) provided the desired result. This allowed unnecessary

configurations to be eliminated from the test matrix.

12
Figure 13. Baseline configuration at Mach=0.78, Alpha=5.2 deg, and Beta=3.0 deg (Point 69).

13
Figure 14. Baseline configuration at Mach=0.78, Alpha=5.2 deg, and Beta=3.0 deg (Point 69)

with sequence average subtracted.

14
Figure 15. 15%Porousplateconfigurationwith plenumat 0.25inches. Mach=0.76,Alpha=5.2

deg,Beta=0.0deg(point 108).

15
Figure 16. Sequence average subtracted from image of 15% Porous plate configuration with

plenum at 0.25 inches. Mach=0.76, Alpha=5.2 deg, Beta=0.0 deg (point 108).

16
Figure 17. Porousplateconfigurationwith 1⁄2 inchdeepplenumcavity. Mach=0.74,Alpha=4.0

deg,Beta=0.0deg(point688).

17
Figure 18. Sequence average subtracted from image of porous plate configuration with 1⁄2 inch

deep plenum cavity. Mach=0.74, Alpha=4.0 deg, Beta=0.0 deg (point 688).

18
6.0CONCLUSIONS

A largefield of view shadowgraphflow visualizationsystemfor theLangley16ft.

TransonicTunnel(16fl.TT) hasbeendevelopedto providefast,low cost,aerodynamicdesign

conceptevaluationcapabilityto supportthedevelopmentof thenextgenerationof commercial

andmilitary aircraftandspacelaunchvehicles.Key featuresof the 16ft. TT shadowgraph

systemare:1)highresolution(1280X 1024) digital snap shots and sequences; 2) video recording

of shadowgraph at 30 frames per second; 3) pan, tilt, & zoom to easily find and observe flow

features; 4) one microsecond flash for freeze frame images; 5) large field of view approximately

12' X 6'; and 6) a low maintenance, high signal/noise ratio, retro-reflective screen to allow

shadowgraph imaging while test section lights are on.

Use of the shadowgraph system during Boeing Airborne Laser Test 534 at 16 ft.

Transonic Tunnel made it possible to successfully evaluate flow control improvements in an

attempt to eliminate unsteady shocks on a laser turret. The availability of the shadowgraph

images depicting ongoing global flow phenomena provided immediate insight into flow

phenomena affecting local pressure responses. The continuous real time information in the

shadowgraph images provided the observer the ability to immediately determine which

configurations: 1) eliminated the unsteady shocks; 2) generated unwanted vortices; and 3)

provided the desired result. This allowed unnecessary configurations to be eliminated from the

test matrix.

7.0 REFERENCES

1. SensiCam Operating Instructions. The COOKE Corporation Ltd. Auburn Hills, MI, June

1999.

2. LS-1130 FLASHPAC Operation Manual. PerkinElmer Optoelectronics, Salem, MA.

3. Innovative Internet Marketing Solutions: About Reflexite - Microprism Technology.

http://www.reflexite.conl/microprism technology.htm Accessed April 18, 2000.

19
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

September 2000 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Development of a Large Field of View Shadowgraph System for a 16 Ft.

Transonic Wind Tunnel WU 992-20-03-31

6. AUTHOR(S)

Michael A. Talley

Stephen B. Jones

Wesley L. Goodman

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

NASA Langley Research Center

Hampton, VA 23681-2199

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

National Aeronautics and Space Administration

Washington, DC 20546-0001

8. PERFORMING ORGANIZATION

REPORT NUMBER

L-18009

10. SPONSORING/MONITORING

AGENCYREPORTNUMBER

NASA/TM-2000-210311

11. SUPPLEMENTARY NOTES

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Unclassified-Unlimited

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Availability: NASA CASI (301) 621-0390

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

A large field of view shadowgraph flow visualization system for the Langley 16 ft. Transonic Tunnel (16 ft.TT)

has been developed to provide fast, low cost, aerodynamic design concept evaluation capability to support the

development of the next generation of commercial and military aircraft and space launch vehicles. Key features

of the 16 ft. TT shadowgraph system are: 1)high resolution (1280 X 1024) digital snap shots and sequences; 2)

video recording of shadowgraph at 30 frames per second; 3) pan, tilt, & zoom to find and observe flow features;

4) one microsecond flash for freeze frame images; 5) large field of view approximately 12' X 6'; and 6) a low

maintenance, high signal/noise ratio, retro-reflective screen to allow shadowgraph imaging while test section

lights are on.

14. SUBJECT TERMS

shadowgraph, wind tunnel, flow visualization, digital images, retro-reflective

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