Closed-Circuit Wind Tunnel (24-inch test)

The Closed-Circuit Wind Tunnel (24-inch test) shall include the following specifications or equivalent (if not brand name):

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 25.908 millimeter (~1.02-inch)-thick grooves placed at approximately 90 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 height and width of 60.96 centimeters by 60.96 centimeters (~24 inches by 24 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).

The test section must also be designed such that a 15-inch section of the usable test area located approximately 6 inches upstream of the nozzle restriction plates can be replaced with a test item without introducing any leaks into the circuit. The total footprint of the tunnel and all associated systems must not be larger than 32 feet in length, 8 feet in width and 7.5 feet in height.

Additionally, portions of 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.

Delivery Location/Address:

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