CLOSED CIRCUIT WIND TUNNEL

Purchase Description 
Procurement of Closed-Circuit Wind Tunnel

Requirements: 
 
• This wind tunnel must be a closed circuit, as the operation of an LDV system 
requires seed particles to be added to the air stream – in this case, a substance 
called Bis(2-ethylhexyl) subacute. The wind tunnel thus needs to be fitted with a 
3/8-inch Swagelok bulkhead fitting placed upstream of the test and transitional 
sections. 

• This wind tunnel must have a maximum operating speed of approximately 50 
meters per second (~9900 feet per minute). The test section walls must have 6.85 
millimeter (0.27-inch)-thick grooves placed at approximately 75 percent of the total 
length of the test section as measured from the entrance in which specialized 
nozzle restriction plates can be affixed to adjust the operating range and achieve 
an air speed of 0.15 meters per second (~30 feet per minute). The typical 
turbulence intensity across this operating range must be less than 1 percent, where 
turbulence intensity is defined as the root-mean-square of velocity fluctuations 
divided by the average test section velocity. 

• This wind tunnel must have a test section size of 101.6 millimeters by 101.6 
millimeters (~4 inches by 4 inches). Test section length can vary if the design 
meets the following requirements: The test section must have at least two sealable 
ports or fittings for the insertion of instruments of various sizes, such as Pitot-static 
tubes and hotwire anemometers. These ports or fittings must accommodate the 
following instrument diameters: 4.3 mm (~0.188 in); 6.3 mm (0.25 in); 7.9 mm 
(0.313 in); 9.5 mm (0.375 in); 10.1 mm (0.4 in); 12.7 mm (0.5 in); 15.9 mm (0.625 
in). One port must be located 49.5 mm (1.95 in) from the inlet, centered into the 
test section; the other port should be offset from this port by 37.5 mm (1.47 in). 
Additionally, the test section sidewalls must be made of optical-quality glass to 
minimize interference with laser propagation. The argon-ion continuous-wave laser 
used in this application has a max wavelength of 532 nanometers and 500 
milliwatts output power. 

• The wind tunnel must have a centrifugal fan design. The fan should be isolated 
from the rest of the tunnel system to minimize vibration. The fan must be controlled 
by a variable-frequency drive (VFD) connected to a motor of appropriate size and 
power to meet the air speed requirements listed above. The VFD must be 
implemented such that an operator could use computer software or manual input to 
control the drive and automate its function. The computer-VFD interface must not 
rely on internet or wireless connections, such as Bluetooth or WiFi. This interface 
must be programmable via National Instruments’ LabVIEW software. 

• Any design submitted must be shown to meet the specific air speed and 
turbulence requirements listed above through a quantitative analysis, such as by 
computational fluid dynamics (CFD) simulations or other appropriate methods.
 

1.0 Delivery Requirements 

Shipping Address: U.S. Army TMDE Activity, Attn: Michael Tyler, Building 5435, 
Redstone Arsenal, AL 35898