Conversion of Purdue’s Mach-4 Ludwieg Tube to a Transonic Educational Facility

AAE 490 Final Report – 12/12/2004

Tyler Wilhelm, School of Aeronautics and Astronautics

Purdue University - West Lafayette, IN ABSTRACT The Purdue University Mach 4 Quiet Flow Ludwieg Tube has been converted to the Purdue Transonic Educational Facility. The conversion involved removing the Mach 4 converging-diverging nozzle and replacing it with a new contraction, flange, and contoured insert section. The new transonic section was prepared during summer 2004, and milled in the Aerospace Sciences Laboratory in August 2004. Assembly and initial testing of the Transonic Educational Facility was performed during the fall semester 2004. INTRODUCTION

Figure 1 – Previous Configuration of Purdue Mach 4 Ludwieg Tube

With the retirement of the Concorde Supersonic Transport, nearly every commercial flight takes place within the range of transonic flight. Purdue University is a leader in Aerospace education, and yet, there has been no facility for examining the properties of transonic flight. Purdue University owned a Mach 4 Quiet Flow Ludwieg Tube at the Aerospace Sciences Laboratory, at the Purdue University Airport, which has set largely unused. The Mach 4 configuration can be seen in Figure 1.

This facility has been replaced by a new Mach 6 Ludwieg Tube with a larger test section and longer test time. In order to utilize the existing resources, the Mach 4 Quiet Flow Ludwieg Tube has been converted to the Purdue Transonic Educational Facility (PTEF). The PTEF is intended to test airfoils at transonic speeds, and will be used primarily as a teaching apparatus for

AAE 520 and for possible demonstrations in AAE 334 Lab. For this conversion, a new contraction, flange, and contoured insert section has been designed and manufactured in the Aerospace Sciences Laboratory machine shop. The new transonic section has been designed so that it is possible for the tunnel to be converted back to Mach 4 operation at a later date. LUDWIEG TUBE OVERVIEW In 1955, German scientist, Hubert Ludwieg proposed a new design for an inexpensive wind tunnel. The design, which became known as a Ludwieg Tube, allows for operation at supersonic, and even hypersonic, velocities, while maintaining relatively quiet flow. This means the data from a Ludwieg Tube more accurately depict flight conditions, when compared to conventional blown-down wind tunnels. Some benefits of the Ludwieg Tube design, adapted from [6] are

• Superior flow quality (shockless inlet design, inherently constant stagnation condtions); flow conditioning and settling chamber not required.

• Pressure regulator not required • The simple design allows operation by a single researcher. Also, a large compressor is

not required, and therefore the cost is kept relatively low.

In order to run a Ludwieg Tube, a burst diaphragm is placed downstream of the driver tube. This diaphragm separates a downstream vacuum from the pressurized air in the driver tube. When the diaphragm is suddenly ruptured, a shockwave is sent downstream, and an expansion wave is sent upstream. The expansion wave reflects off the closed end of the driver tube, and typically continues reflecting until the pressure nears equilibrium. Between passes of the expansion wave, the flow in the test section is quasi-static, allowing data to be obtained.

DESIGN FOR TRANSONIC CONVERSION CONTRACTION The Mach 4 Ludwieg Tube had a converging-diverging nozzle, which is required for supersonic flow. The PTEF is not intended to reach supersonic freestream conditions, and therefore needs only a contraction. The contoured insert section, which is discussed later, takes the place of the Mach 4 diverging nozzle. The transonic contraction was designed in 1998 by Shin Matsumura, who was an undergraduate student at Purdue University. The contraction uses a superellipse function to transition from a circular driver tube, with an inner radius of 6.033 inches, to the contoured insert section with an inner width of 3.804”, and an inner height of 4.325”. The general form of a superellipse is given as

100

=

+

aa

yy

xx

In this equation, x0 and y0 are respectively the semi-major and semi-minor axis parameters. The parameter ‘a’ controls the shape of the cross section. This equation reduces to the formula for a circle with radius x0 when x0 and y0 are equal, and ‘a’ is 2. As ‘a’ increases, the cross section becomes more rectangular. More details of how the contraction contour was designed can be found in reference [1]. The contraction section must also be designed so that it

slides into the end of the driver tube. A Matlab script was written that produced the Cartesian coordinates (X,Y,Z) for the contraction contour. These coordinates were used to create a nurb surface in SURFCAM, which was then used to create the CNC code for the milling machines. The contraction was milled from an aluminum cylinder with an initial diameter of 13 inches, and height of 13 inches. To begin fabrication of the contraction section, a majority of the material was removed using a lathe. The cylinder was then cut to a height of 12.315 inches, and then cut down the center, creating two identical halves. The final contraction contour was then milled with a 3-axis CNC milling machine. When the contour was finished, the halves were bolted back together to form the contraction insert. The contraction insert has an outer diameter of 12.290 inches, and a height of 12.315 inches. This contraction will then slide into the end of the driver tube. This contraction insert is the same size as the current Mach 4 contraction insert, which allows conversion back to Mach 4 capabilities at a later date. FLANGE Between the contraction insert and the contoured insert section is a blind flange modified for this Ludwieg Tube. The contraction contour continues from the contraction section through the modified blind flange. The modifications include milling the final portion of the contraction from the center of the flange, holes for attaching the contoured insert section, and alignment holes. The flange was machined to a final thickness of 1.185”. This gives a complete contraction length of 13.50 inches. CONTOURED INSERT SECTION

Figure 2 – New Configuration of Purdue Transonic Educational Facility

The goal of the Purdue Transonic Educational Facility is to test airfoil sections at transonic speeds. Preliminary design of the contoured insert section (CIS) was also done by Shin Matsumura. The CIS was initially envisioned to achieve a Mach number of 0.722 with a model chord length of 3 inches. More details can be found in reference [2]. Figure 2 shows the complete configuration of the PTEF. The CIS is designed as an adaptable wall test section. An adaptive wall test section allows the flow streamlines to adapt to the body. The streamlines are able to move away from the body, which prevents the flow from choking around the model. Instead of utilizing flexible walls, like many other tunnels, the CIS was designed with contoured wall inserts. Both the wind tunnels presented later in this section use flexible adaptive walls.

The advantage of contoured inserts is the relatively low cost of initial design and fabrication. An additional advantage with the CIS, is that the top and bottom are designed so that the contoured insert can be in as many as 3 pieces, which has the potential to cut down material cost. The disadvantage of contoured inserts lies in the requirement for a different insert for each individual test. It is important that the height of the contour be maximized to allow for the maximum streamline deflection.

The size of the contoured inserts was determined by studying various wind tunnels with adaptive wall test sections. The Cryogenic Ludwieg Tube at DLR in Göttingen, Germany has a 2.0 m x 0.4 m x 0.35 m test section. (reference [5]) The maximum wall deflection is 0.045 meters. This gives a maximum deflection to test section height ratio of 12.86%. The Transonic Cryogenic Tunnel at NASA Langley Research Center has a test section height of 13 inches, with a maximum wall deflection of 3 inches. (reference [4]) That gives a maximum deflection to height ratio of 23.08%.

The CIS has an inner width of 3.804” and an inner height of 4.325” for testing of a model with a 3 inch chord (from reference [2]). In order to meet the existing test section, it was determined that the maximum thickness for the inserts would be 1 inch. With a test section height of 4.325 inches, this gives an insert to test section height ratio of 23.12%. This is greater than the German tunnel, and has almost the exact same ratio as the NASA tunnel. In subsonic flow, unlike supersonic flow, disturbances can propagate upstream. This means the flow will start to diverge before actually reaching the body. This makes the distance from the beginning of the adaptation to the leading edge of the model an important design criterion for a transonic wind tunnel. For the NASA tunnel, the flexible section starts 23.25 inches in front of a 13 inch model. The ratio between model chord and distance is 55.91%. In the CIS, the insert starts 5.565 inches in front of the leading edge. Based on a model chord of 3 inches; this gives a ratio of 53.91%. This allows maximum adaptation of the flow, while meeting all design conditions.

One design condition that needed to be met was the windows in the CIS. The two upstream windows, and the middle set of windows were designed to be in the same position relative to the flange as the windows in the Mach 4 nozzle. The middle set of windows, as well as the two downstream windows, are designed to be in the same position relative to the test section as the windows in the Mach 4 nozzle. Figure 3 show the window openings in the CIS, covered by solid aluminum blanks. The upstream direction is to the right. The glass windows are mounted in aluminum frames using Cerrotru, and are interchangeable with the test section, as well as the Mach 4 nozzle.

Figure 3 – Window openings (covered) in CIS

The cut-out in the top wall of the CIS is due to the traversing mechanism in the test section. The traverse cover plate extends up to 4.5 inches into the area above the contoured insert section prompting the 5 inch long cut-out. Due to the cutout in the top wall, the CIS is 5 inches longer than the Mach 4 nozzle. An identical cut out is present in the bottom wall of the CIS, so that if the need should ever arise, it is possible to rotate the CIS 180o, while only changing the downstream flange. Figure 4 is a photograph of the assembled Transonic Educational Facility.

Figure 4: Assembled Transonic Educational Facility

THE PURDUE TRANSONIC EDUCATIONAL FACILITY The Purdue Transonic Educational Facility was originally constructed between 1992 and 1994 as the Purdue Mach 4 Quiet Flow Ludwieg Tube. The PTEF was designed to utilize as many of the same parts of the Mach 4 Ludwieg Tube as possible, in order to reduce fabrication cost and to allow conversion back to the Mach 4 capability at a later date. The 68 foot long driver tube section of the Ludwieg Tube is standard weight (150 psi class) carbon steel pipe with an inner diameter of 12 inches. The driver tube extends into the laboratory area, where it is held 8 feet overhead by I-beam columns. Before assembly, the pipe was sand-blasted and painted to eliminate interior rusting and particle formation. For a run, the driver tube can be set at any desired pressure. The pressure must be kept below 30 psia to prevent damage to electronic equipment. The driver tube is connected to the vacuum section through a small pipe, which, when opened, allows the initial pressure of the driver tube to be set below atmospheric pressure. The driver tube is also attached to an Ingersoll Rand PA50 215 SCFM 120 psig 50 HP compressor, which allows the driver tube initial pressure to be set above atmospheric pressure. The compressor is also used to pump the Ludwieg Tube back to atmospheric pressure after a run has been completed.

The transonic contraction is 13.5 inches long, and matches to the contoured insert section which has an inner width of 3.804 inches, and an inner height of 4.325 inches. The design of the CIS was discussed previously. The CIS then mates to the test section. The test section was developed for the Mach 4 Ludwieg Tube, and is also used for the Purdue Transonic Educational Facility. The test section currently houses a double wedge, which is 1 inch wide at its widest part and acts as the downstream throat. The double wedge also incorporates a sting support for testing various models.

The vacuum system of the Ludwieg Tube uses two vacuum pumps to evacuate the downstream section of the Ludwieg Tube, as well as a 535 cubic foot vacuum tank. The pumps use vacuum lines made from standard 12 inch pipe. The two pumps can pump-down the vacuum section to less than 1 torr, though the Ludwieg Tube is normally run at a vacuum pressure of about 4 torr. When the pressure rises above atmospheric pressure, the vacuum lines are evacuated using a check valve made from a flapping blind flange hinged to a tee, sealed with an o-ring. With a combined pumping rate of 270 cfm, the vacuum section can be pumped down to 4 torr in about 15 minutes.

Between the vacuum section and the test section is the diaphragm section. Easy placement and removal of the diaphragm apparatus is facilitated by a quick-opening yoke coupling, manufactured by Tube-Turns Inc. The diaphragm section is opened and closed using a hand-operated hydraulic pump. Mylar burst diaphragms are used to separate the downstream vacuum from the pressurized air upstream. Typically for driver tube initial pressures up to 10 psia, 0.004 inch thick Mylar is used for the burst diaphragm. Driver tube pressures between 10 and 18 psia typically uses 0.007 inch thick diaphragms, while higher pressures use a 0.010 inch thick diaphragm. Nichrome wires are taped to the diaphragm in an “X” pattern. In order to break the diaphragm, the nichrome wires are attached to “a pulsed heating apparatus consisting of 0.76F of 40V capacitors that are discharged through a high power SCR (International Rectifier ST230S16P0)”[8]. When the 20A of current is passed through the nichrome wires, the wires become very hot, melting the Mylar and causing it to burst, initiating the run. A typical run last between 3 and 5 seconds, with each reflection of the expansion wave taking about 0.08 seconds. This means that in a typical run, there are over 30 quasi-static run segments from which data can be obtained.

Data is recorded in the Purdue Transonic Educational Facility with a Kulite pitot probe placed into the flow, near the middle window of the contoured insert section. A static pressure transducer on the side wall of the test section is also utilized. Data from these pressure probes is collected by a LeCroy 9104 digital oscilloscope, and transferred to a computer using the Scope Explorer program. Fluctuations in pressure during the quasi-static run segments are typically no more than 0.3%. These two pressure readings are used to calculate the Mach number using equation 1.

( )

−

−

=−

11

2/)1

1

1,021

γγ

γ pp

M (1)

Velocity can be calculated from Mach number by determining the speed of sound. The speed of sound is given by the following equation

∞∞ = RTa γ (2) Where γ is 1.4, R is the ideal gas constant, and T∞ is the freestream temperature. The freestream temperature can be determined by the isentropic relation

−∞

=γγ 1

0

0

PP

TT (3)

With the universal gas constant R taken to be 1716 ft*lb/slug*oR, the freestream velocity is given by

∞∞ = aMU *1 (4)

Assuming the flow in the Ludwieg Tube will choke at the downstream throat during the run, the theoretical Mach number can be calculated from the ratio between the cross sectional area in the CIS, and the cross sectional area of the throat. If the cross sectional areas are known, Mach number can be calculated from

)1/()1(2

2

2

* 211

121

−+

−+

+=

γγγ

γM

MAA (5)

As mentioned previously, the CIS was initially designed to operate at a Mach number of 0.722. For the PTEF, the CIS cross sectional area is 0.1143 ft2, and the cross sectional area at the throat is 0.0842. This gives a ratio of 1.3575, which corresponds to a Mach number of 0.4917, when γ is considered to be 1.4. With the current downstream throat, the Mach number in the CIS will not reach the design condition. The Mach number could be increased with a smaller double wedge. However this poses two problems. This first is that any changes in the sections which are used by both the Mach 4 Ludwieg Tube and the PTEF would need to be restored before conversion back to Mach 4 operation, which complicates the conversion process.

The second problem is that by choosing a Mach number of 0.722 and solving equation (5) for the cross sectional area of the throat, the maximum width of the double wedge is 0.2794 inches. As mentioned before, the double wedge also incorporates the sting support for test models. The current support is threaded for a ½-13 sting. With the width of a new double wedge being 0.2794 inches, this means the existing sting supports will have to be modified, or a new method for holding the models will have to be found. TESTING PROCEDURE A typical run should take between 25 and 35 minutes, depending on the desired pressures.

1. Turn on Oscilloscope, Kulite boxes, capacitor, and computer. Capacitor takes some time to build up charge, best to have on while pumping down tunnel. Make sure oscilloscope is turned on before the computer.

2. Make sure red handled valve which isolates the Ludwieg Tube from the supersonic tunnel is set for Ludwieg Tube operation.

3. On computer, Open Scope Explorer program, choose Scope>Scope Finder, and choose “Find” to verify the connection between the computer and oscilloscope.

4. Prepare diaphragm, as described in next section 5. Open Tube-Turns, fit diaphragm ring in tunnel, Close Tube-Turns to seal tunnel. 6. Turn on cooling water; keep water approximately at the midpoint of the glass.

7. Start the Stokes pump (on the left facing the pumps), open the red handled valve. While pumping, observe pump temperature, and keep below 140oF. If temperature gets to high, check that cooling water is running.

8. Start the other pump (on the right), and open blue handled valve. 9. Set desired driver tube pressure, either by opening green valve (raising pressure), or by

opening yellow valve (lowering pressure), or by running at atmospheric pressure. 10. Prepare next diaphragm while waiting for tunnel to pump down the vacuum section. 11. Turn off pumps when desired vacuum reached 12. Turn on trigger switch on diaphragm breaker box, set oscilloscope to “single”, and on

Scope Explorer on the computer, choose terminal>remote 13. Fire tunnel, by touching red wire to opposite post, closing the circuit. 14. Turn off trigger switch on the diaphragm breaker box 15. Open green valve to return tunnel to atmospheric pressure 16. While tunnel is re-pressurizing, on the computer, in Scope Explorer, choose “Traces”,

and select desired channels, and obtain traces in ASCII form. Save for analysis, then choose terminal>local.

17. Remove used diaphragm, and insert new diaphragm, repeat steps 5 thru 16 DIAPHRAGM PREPARATION To begin a run of the Ludwieg Tube, a Mylar burst diaphragm must be prepared. If a diaphragm is not available, one must be traced and cut out of Mylar. For these tests, the diaphragms were prepared in June 2004. The first step is to insert the Mylar diaphragm into the diaphragm ring. The ring is then bolted together using two small dowel pins to align the ring. Once the diaphragm has been secured in the ring, nichrome wires are taped to the upstream side of the diaphragm in an “X” pattern. The top wire is made to loop over the bottom wire so the wires will not short each other out. Figure 5 shows how the diaphragm is set up

Figure 5 – Burst Diaphragm Setup (from reference [8])

CALIBRATION In order to get accurate measurements from both the pitot and static pressure probes, the tunnel was pressurized to a known pressure, read with a Paroscientific 740-30A pressure gauge, and the corresponding voltages were read with an HP 34401A digital multimeter. The calibration for each probe was performed over a range from about 0.2 psia to atmospheric pressure, and then a linear fit was applied to the results. The linear fit allows a conversion between voltage and psia.

Figure 6 – Pitot Pressure Calibration Figure 7 – Static Pressure Calibration

Figure 6 shows the calibration for the Kulite pitot probe. Two calibrations were completed, and both data sets matched quite well. A linear fit was applied to the second calibration data, to give a conversion from voltage to pressure of

4414.10744.11,0 += Vp (6) This formula compares favorably to the calibration of the same pitot probe by Borg and Smith [7] which gave a conversion of

7651.10736.11,0 += Vp Figure 7 shows the static pressure calibration. Three calibrations were performed for this

probe. The third calibration was run because of the divergence between calibration 1 and calibration 2 below 4 psia. The second and third calibrations matched reasonably well. A linear fit was applied to the third calibration, which gives a conversion from voltage to pressure of

039582.09586.21 += Vp (7)

INITIAL TROUBLESHOOTING Initial testing of the Transonic Educational Facility focused on verifying the testing procedure, troubleshooting, and examining the effects of initial driver tube pressure on Mach number. The testing procedure was detailed in the previous section. Troubleshooting became a major factor in this project. Upon the first run of the Transonic Educational Facility, it was determined that the Kulite box was not sending the proper voltage signal to the oscilloscope. At first it was thought to be a

problem with the Kulite box, so another box was obtained. However, the problem was not resolved. Further investigation showed that the +15 V wire was not providing any power to the Kulite box. The wire had been broken near the connector end, so the broken part was removed, and the connector was soldered back in place. With the power issue resolved, an attempt was made to begin testing the tunnel. When the data collected by the computer was analyzed, the static pressure, calculated with equation (7) was found to be about 2 psia less than expected. After reviewing the recorded voltage data, it was found that the data did not match the voltage recorded by a multimeter attached to the Kulite box. The problem was resolved by changing the volts/div setting on the oscilloscope from 5 volts/div to 2 volts/div. It was also noticed during this time, that the tunnel was leaking around the downstream end of the contoured insert section. Additional RTV sealant was added, which slowed the leak, but the tunnel still seems to be leaking. However, this leak did not seem to have a major impact on the results of the initial tests. INITIAL RESULTS To examine the effects of various initial driver tube pressures on Mach number, three tests at each of four different driver tube initial pressures were performed. Tests were performed at driver tube pressures of approximately 10.60, 12.55, 14.45, and 16.40 psia. All tests were performed with a vacuum pressure of approximately 4 torr (0.0773 psia). The lowest initial pressure tested for this experiment was approximately 10.60 psia. Figure 8 shows the pitot and static pressure, averaged over the 3 separate runs.

Figure 8 – Pitot and Static Pressures for initial pressure of 10.60

The average pitot pressure, calculated from equation (6), for the first pressure step after startup was calculated to be 9.9257 psia, and the average static pressure, calculated from equation (7), for the first step was calculated to be 8.1281 psia. Equation (1) produces an average Mach number of 0.5420. This is slightly higher than the expected Mach number. This is because as pressure decreases, so does the speed of sound. This means that for the same velocity, the Mach

number will be higher. Using equations (2), (3), and (4), the average velocity for the first pressure step was calculated to be 592.6703 ft/s. The next initial pressure which was used was approximately 12.55 psia. The average pitot and static pressures can be seen in Figure 9.

Figure 9 – Pitot and Static Pressures for initial pressure of 12.55 psia

Using equation (6), the average pitot pressure for the first pressure step after startup was calculated to be 11.7746 psia, and the average static pressure, from equation (7), for the first step was 9.6934 psia. Using equation (1), the average Mach number is calculated to be 0.5345. Again this is higher than the theoretical Mach number, but it is also slightly lower than the Mach number calculated with an initial pressure of 10.60. With a higher pressure than the previous test, the speed of sound is greater, which lowers the Mach number. Using equations (2), (3), and (4), the average velocity for the first pressure step was calculated to be 591.3575 ft/s. This velocity is very close to the velocity calculated for the first pressure case. The slight difference could be due to the averaging of the 3 separate runs. This demonstrates how initial pressure affects Mach number, though not necessarily velocity. The third initial pressure tested was approximately 14.45 psia. Figure 10 shows the pitot and static pressure traces, averaged over 3 separate runs.

Figure 10 – Pitot and Static Pressures for initial pressure of 14.45 psia

The average pitot pressure, calculated from equation (6), for the first pressure step after startup was calculated to be 13.4932 psia, and the average static pressure, calculated from equation (7), for the first step was 11.1834 psia. Using equation (1), the average Mach number was calculated to be 0.5249. Following the same trend, the Mach number is lower than previous tests, but still higher than the theoretical Mach number. Using equations (2), (3), and (4), the average velocity for the first pressure step was calculated to be 578.1155 ft/s. This is lower than the previous two cases, though not by a large amount. The final test conditions are an initial pressure of approximately 16.40 psia. The average pitot and static pressure traces can be seen in Figure 11.

Figure 11 – Pitot and Static Pressures for initial pressure of 16.40 psia

An anomaly can be seen in the average pitot pressure trace in Figure 11. The Kulite probe has an electronically set maximum voltage, to prevent damage to the electronics. The maximum voltage was expected to be between 13 and 15 volts. However, the maximum voltage recorded in each of the 3 runs was 12.3875 V. This corresponds to a maximum pressure reading of 14.75 psia. This clipping effect causes the calculation of average Mach number for the first pressure step to be incorrect. To perform a proper comparison, the first pressure step after startup should be used. However, since this pressure step is incorrect, the second pressure step is chosen for analysis. Direct comparison will not be very useful, but the pressures and Mach number should follow the same trend as the other cases. The average pitot pressure for the second pressure step is 13.1077, and the average static pressure for the second step is 10.8181. The average Mach number for the second pressure step is 0.5310. Because these values are taken from the second pressure step, the pressures are lower, and fall between the values obtained from the runs with an initial pressure of 14.45 psia, and the runs at 12.55 psia. The velocity calculated for this pressure step by equations (2), (3), and (4), is 500.8962 ft/s. This is significantly lower than the velocities obtained from the previous 3 cases. However, this is to be expected because the data was taken from the second pressure step. SUMMARY AND CONCLUSIONS The Purdue University Mach 4 Quiet Flow Ludwieg Tube has been converted to the Purdue Transonic Educational Facility. The PTEF has been prepared for use in AAE 520 during the spring 2005 semester. The PTEF was designed for a freestream Mach number of 0.722. However, with the current downstream throat, the Ludwieg Tube theoretically chokes around a Mach number of 0.4917. Results of the initial testing show that as the driver tube initial pressure increases, the Mach number decreases. This is because as pressure increases, so does the speed of sound. The speed of sound is then inversely proportional to the Mach number. So for the same velocity, Mach number will be higher at lower initial pressures. RECOMENDATIONS Before embarking on any scientific research with the PTEF, the leaks near the connection between the CIS and the test section need to be isolated, and repaired. The solution could be as simple as adding more RTV sealant in the correct place, or the problem could lie with the o-ring not sealing properly.

One issue for future consideration is to examine changing the double wedge in the test section to achieve a higher freestream Mach number. The pros and cons of changing the throat should be weighed with consideration to future plans with the Mach 4 nozzle.

Another consideration for future use is to examine reference [2], and refine the process for calculating the contours which will need to be made for a model to be tested in the PTEF.

References [1] Matsumura, Shin. “AAE490 – Design of a Contraction for a Transonic Ludwieg Tube: Report 3.” Purdue University. 11/30/1998. [2] Matsumura, Shin. “AAE415 – Design of a Test Section for a Transonic Ludwieg Tube: Report 4.” Purdue University. 12/17/1998. [3] Meyer, O., and W. Nitsche “Update on progress in adaptive wind tunnel wall technology.” Progress in Aerospace Sciences 40 (2004) 119-141. Technical University of Berlin. 2004. [4] Allison, Dennis O., and Raymond E. Mineck. “Assessment of Dual-Point Drag Reduction for an Executive-Jet Modified Airfoil Section.” NASA Technical Paper 3579. NASA Langley Research Center. July 1996 [5] Rosemann, H., and E. Stanewsky and G. Hefer. “The Cryogenic Ludwieg Tube of DLR and Its New Adaptive Wall Test Section.” AIAA Paper 95-2198 Institute of Fluid Mechanics, Göttingen, Germany [6] Schneider, Steven P. “A Quiet-Flow Ludwieg Tube for Experimental Study of High

Speed Boundary Layer Transition”, AIAA Paper 92-3885, Purdue University, West Lafayette, IN

[7] Borg, Matt, and Justin Smith. “Effects of Disturbances on Quiet Flow in the Mach 4

Ludwieg Tube”, AAE 520 Final Report, Purdue University, 5/5/2004 [8] Schneider, Steven P., et al., “Laminar-Turbulent Transition Research in the Purdue

Mach-4 Quiet-Flow Ludwieg Tube”, AIAA Paper 96-2191, Purdue University, West Lafayette, IN

Appendix: Technical D

rawings