SUPERSONIC WIND TUNNELS (UPDATED)

Compressible flow courses are included in all Aerospace and Mechanical engineering curricula. For students, wind tunnel experience with shock and expansion waves makes an excellent addition to theoretical studies. AEROLAB offers variable Mach number supersonic wind tunnels in test section sizes from 1" x 1" to 12" x 12".

All AEROLAB supersonic wind tunnels employ a sliding block design that was originally developed for NASA and then later improved by the University of Michigan. Surveys of Mach number and angularity deviations are available for these contours which show high-quality flow over the Mach number range of l.5 to 3.5 for the 1 and 2-inch tunnels and l.4 to 4.0 for our larger tunnels. Copies of these flow surveys are available upon request.


DISCUSSION OF VARIABLE MACH NUMBER NOZZLES

In the 1950s, Mr. “Harvey” Julian Allen of the Ames Laboratory of NASA developed a new concept for variable Mach number tunnel design using two solid nozzle blocks with the lower block movable in the flow direction with respect to the upper. This “sliding block” nozzle was later employed in four large NASA tunnels, namely the Ames 6 x 6-foot, the Ames 7 x 9-foot and the two Langley 4 x 4-foot tunnels. Since these tunnels offered rather limited Mach number range, the Air Force (in 1951) awarded a contract to the University of Michigan to extend the Mach number range of sliding block nozzles. In the course of the next six years a team of research workers carried out a theoretical analysis, built an experimental nozzle according to the theoretical contours and experimentally varied the theoretical contours until optimum flow was achieved. The Mach number range was approximately doubled and the flow quality was much improved with respect to the NASA tunnels. These contours are used in all AEROLAB Supersonic Wind Tunnels.

AEROLAB variable Mach number wind tunnels are available in two configurations:

"Console ” – for our 1-inch (2.54cm) and 2-inch (5.08cm) systems
"Standard ” – for our 3”x3”, 4”x4”, 6”x6”, 8”x8”, and 12”x12” systems

Console systems are complete, compact supersonic wind tunnel laboratories requiring only compressed air. These systems include an oil separator, a heatless desiccant air dryer, ASME Code storage and stagnation tanks, an electro-mechanical pressure control valve, a complete Schlieren system, a set of four models, a model positioning “quadrant” and a diffuser.


Console System



Standard systems include an electro-mechanical pressure valve, an ASME Code stagnation tank, the supersonic wind tunnel and diffuser. These systems require a compressor, oil separator, dryer, storage tank and all associated plumbing



Standard System (valve and actuator not shown)

Recommendations and quotations (inc. storage tanks and compressors) are available upon request.

All AEROLAB supersonic wind tunnels include:

4 National Instruments ™ / LabVIEW ™ data acquisition, display and control system. The system displays (real time) and records storage tank pressure, stagnation pressure, stagnation temperature, nozzle block position, test section static pressure, “sting” force balance output (optional) and model pitch angle (only available with optional motor control). The system controls stagnation pressure and nozzle block position. Model pitch angle control is available as an option.

4 Dell desktop computer with an executable LabVIEW ™ file. (LabVIEW software is not needed.)
4 Electro-mechanical pressure valve. Controlled by LabView, this device provides fast ramp-up and stable stagnation pressure.
4 Stagnation tank. An ASME Code bell-shaped tank with a steel perforated flow-smoothing baffle plate.
4 Stainless steel turbulence-reducing screens. Two, 20 x 20 mesh screens down-stream of the perforated baffle smooth the flow before it enters the contraction. The contraction area ratio is in excess of 30:1.

4 Motor-driven adjustable nozzle blocks. Using a contour developed at the University of Michigan, blocks are machined and accurately ground from solid aluminum with Teflon and rubber seals.

4 Test section. Made of heavy steel plates and surface ground on the inside, deformation is not an issue.
4 Windows. Made of polished plate glass and selected for Schlieren uniformity. One on each side.
4 4-piece stainless steel supersonic model set (sphere, wedge, cone and total pressure probe)
4 Model positioning system – “quadrant” style with manual adjustment and Veeder-root indicator.


LabVIEW display for special-order 1" system

Available options include:
4Motorized and computer controlled model pitch angle (positioning quadrant).
4Strain gage “sting” balance (avail. for ≥ 2” wind tunnels, see below) w/ model pos. quadrant
4Specialty models including AGARD, force missile and pressure missile


Strain Gage Force Balance on "Quadrant"
Force Missile and AGARD Models


CONSTRUCTION

All AEROLAB supersonic pressure vessels are ASME certified to 200 psi (1.28 MPa). A LabVIEW-controlled actuator/valve holds constant stagnation pressure during a run as storage pressure diminishes.

2-Inch Tunnel Control Valve and Actuator



For tunnels larger than 1-inch, the air flow is made uniform and steady through the stagnation section by means of a perforated plate and two 20x20 anti-turbulence screens. A welded steel entrance cone guides the air into the rectangular channel between the nozzle blocks. The area ratio is in excess of 16:1 at all Mach numbers.


Supersonic turbulence reducing screens and contraction assembly

Several static pressure orifices are provided in the test section to guard against errors resulting from shock-wave boundary-layer interactions.

The nozzle blocks are machined from solid aluminum to close tolerances and with excellent surface finish. The heavy construction provides assurance that pressure forces upon the nozzle will not cause appreciable change of the nozzle contour. The blocks are ground upon their lateral surfaces as well as upon the nozzle surface to offset warpage during machining. The lower block is sealed with a Teflon strip for low sliding friction. The front corners of the block are rounded and fit within a section of the tunnel with rounded corners to seal at the high pressure end. Wide keyways are machined on each side of the lower block to hold it rigidly in place The side walls of the test section are made of l½ inch (3.81cm) steel surface ground on the inside. The windows are of 1¼ inch (3.175cm) optical-quality glass selected for Schlieren viewing.

View of Supersonic windtunnel with one side plate removed.

 


Looking down the throat of a 3-inch -Inch Supersonic Wind Tunnel

Nozzle block position (Mach number), too, is actuator-controlled by LabVIEW.

The supersonic diffuser is a straight parallel channel about 12 test sections in length. A sliding block in the bottom furnishes a smooth continuation of the flow over the lower nozzle block.


Diffuser on a 2-inch System

 

WINDOWS

The test section windows must fit accurately and flush with the interior surfaces of the side plates to avoid flow disturbances. In the standard design the windows are permanently installed. As an option, windows can be installed in aluminum frames which are carefully hand fitted to the side plates or solid blanks may be fitted to the window openings. If a tunnel is ordered with blanks, Schlieren quality windows may be fitted at a later date.


The test section of a 3-inch supersonic tunnel with a removable window.



OPERATION

Access to the test section is obtained by loosening two knobs and sliding the track-mounted diffuser downstream, away from the test section. Because our model positioning system (angle of attack “quadrant”) is fastened to the diffuser, access to the model is quick, unhindered and convenient. If desired, the angle of attack quadrant may be removed.


Test section and Diffuser Latches on 2-inch Console System

For a user-defined Mach number, the LabVIEW interface suggests a nozzle block position and stagnation pressure from calibration data. The user can choose these suggestions, or alter them as needed for higher Reynolds number runs. The tunnel is started and stopped with a mouse click. The tunnel will stop automatically when storage pressure drops to within 10 psi (69 KPa) of the needed stagnation pressure.

 

INSTRUMENTATION

The console systems are supplied with a complete Schlieren system – it is an option for the standard systems. Sting internal Force/Moment Balance Systems are available for all tunnels except the 1” model.