September 2000

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
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September 2000

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
Available from:

NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS)

7121 Standard Drive 5285 Port Royal Road

Hanover, MD 21076-1320 Springfield, VA 22161-2171

(301) 621-0390 (703) 605-6000
i

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
ii

List of Figures

Page

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

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

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

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

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

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

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

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

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

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

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

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

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

deg, Beta=0.0 deg (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. Porous plate configuration with 1⁄2 inch deep plenum cavity. Mach=0.74, Alpha=4.0

deg, Beta=0.0 deg (point 688). ............................................. 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
1

ABSTRACT

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.

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 ft.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
2

Digital Image Acquisition

Using Computer & Frame Grabber

Shadowgraph

Camera & 

Light Source

Plenum

Window

Test Section

Window

12’ X 6.5’ RetroReflective Screen

Digital Image Acquisition

Using Computer & Frame Grabber

Shadowgraph

Camera & 

Light Source

Plenum

Window

Test Section

Window

12’ X 6.5’ RetroReflective Screen

Figure 1. Shadowgraph configuration at 16 ft. TT.

test section wall approximately 30 ft. from the camera. A field of view of approximately 9 ft. by

5 ft. at the center of the test section will require the screen to be 12 ft. wide by 6.5 ft. high. The

computer used for digital image acquisition, VHS tape recorder, and all system controls must be

located in the control room. A generic shadowgraph configuration that meets these constraints is

shown in Figure 1.

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 flash2 for freeze frame images;
3

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

Figure 3. Layout of light source and camera.

5) large field of view approximately 12' X 6'; and 6) a low maintenance, high signal/noise ratio,

retro-reflective3 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.
4

Monitor

Windows Computer

Camera

Interface

Network

Connection

Trigger/

Delay Box

Flash

Power

Supply

Short Arc Xenon Flash

Cooke SensiCam

Digital Camera

Fiber Optic Interface Cables

(100 Meters)

Tunnel Mezzanine

Tunnel Control Room

Flash Trigger

(50 Ohm Coax )

Figure 4. Digital shadowgraph system.

Video Monitor

S-VHS VCR

Video

Flash

Synchronizer

Flash

Power

Supply

Short Arc Xenon Flash

Video Camera

Tunnel Mezzanine

Tunnel Control Room

Flash Trigger

(50 Ohm Coax )

Video Inserter

(Tunnel Parameters)

Zoom Lens

Control

Pan/Tilt

Video (50 Ohm Coax)

Figure 5. 30 frame pers second video system.

Block diagrams showing components of the digital and 30 frame per second video

systems are shown in Figure 4 and Figure 5 respectively.
5

Figure 6. Control room image acquisition station.

A picture of the image acquisition station in the control room is shown in Figure 6.

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.
6

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

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

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

5.0 TESTS & RESULTS

5.1 Lab Tests

The digital and video shadowgraph systems were tested in the lab using a complete mockup of the 16 ft. TT optical layout. Figure 9 shows a shadowgraph image of flow from a heat gun

acquired from the digital camera at a resolution of 1280 X 1024. The heat gun was 22 ft. from

the camera and the reflexite screen was 30 ft away. The field of view was 50 in. high

corresponding to an image resolution just under 0.05 in. per pixel.

Figure 9 was enhanced by subtracting a background image in which the heat gun was

removed. The result is that more flow detail can be seen as shown in Figure 10. This
9

Figure 10. Heat gun flow after background subtraction.

enhancement technique provides significant improvement, however, the location of the retroreflective screen must stay fixed relative to the shadowgraph camera.

5.2 Tests to Assess Background Subtraction Technique

Background subtraction was not possible due relative displacement of the test section

wall with respect to the shadowgraph camera location. Horizontal relative displacements of 3

targets (X1, X2, and X3) on the test section wall were measured from the shadowgraph camera

location using video photogrammetry. Over 700 data points were taken over an operational

range of Mach 0 to Mach 1.2 where the tunnel air temperature ranged from 65F to 170F. The

displacement for each target at each data point is plotted with respect to the air temperature as

shown in Figure 11. Measured vertical displacements were insignificant.
10

Test Section Horizontal Wall Displacement VS Air Temperature

y = 0.0029x - 0.1924

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

60 80 100 120 140 160 180

Temperature, F

Displacement, Inch

X1 data

X2 data

X3 data

Linear (X2 data)

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

Patch 1

Patch 2

Patch 3

Porous or Solid Plate

Plenum

Typical Dynamic Pressure Tap

Typical Steady State Pressure Tap

Patch 1

Patch 2

Patch 3

Porous or Solid Plate

Plenum

Patch 1

Patch 2

Patch 3

Porous or Solid Plate

Plenum

Typical Dynamic Pressure Tap

Typical Steady State Pressure Tap

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

5.3 Aerodynamic Tests in the 16 ft. TT

Use of shadowgraph measurement technique 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. This was possible due to the

visualization of flow features associated with different aerodynamic configurations of the laser

turret cover plates. Figure 12 shows the laser turret and location of cover plates. Test results

from three plate configurations which demonstrate different flow features have been selected for

discussion. These are: the baseline plates; plates with 15% porosity and 1/4 in. plenum depth;

and plates with 25% porosity and 1/2 in. plenum depth. The 25% porosity plates were partially

covered with Patch 1 as shown in the figure.

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.
12

Table 1

Turret Plate

Configuration

Test

Conditions

Notable flow features Images Showing

Features

Baseline - no

porosity

Mach=0.78

Alpha=5.2

Beta=3.0

Unsteady lambda shock followed

by recirculating turbulent flow

below a low angle free shear layer

Figure 13 & Figure 14

15% Porosity

with 1/4 in.

Plenum

Mach=0.76

Alpha=5.2

Beta=0.0

Recirculating turbulent flow below

a high angle free shear layer - no

lambda shock formation 

Figure 15 & Figure 16

25% Porosity

(Patch 1) with

1/2 in. Plenum

Mach=0.74

Alpha=4.0

Beta=0.0

Significant vortex formation &

bursting below the free shear layer

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.
13

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

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

with sequence average subtracted.
15

Figure 15. 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 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).
17

Figure 17. Porous plate configuration with 1⁄2 inch deep plenum cavity. Mach=0.74, Alpha=4.0

deg, Beta=0.0 deg (point 688).
18

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).
19

6.0 CONCLUSIONS

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 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.com/microprism_technology.htm Accessed April 18, 2000. 
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

September 2000

3. REPORT TYPE AND DATES COVERED

Technical Memorandum

4. TITLE AND SUBTITLE

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

Transonic Wind Tunnel

5. FUNDING NUMBERS

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

8. PERFORMING ORGANIZATION

REPORT NUMBER

 L-18009

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

National Aeronautics and Space Administration

Washington, DC 20546-0001

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA/TM-2000-210311

11. SUPPLEMENTARY NOTES

 

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Unclassified-Unlimited

Subject Category 35 Distribution: Nonstandard

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

15. NUMBER OF PAGES

26

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A03

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