Subsonic Wind Tunnels
The Hessert Center is equipped with two similar, horizontal, subsonic open-circuit wind tunnels, recognized internationally for their flow visualization capability. Each indraft tunnel has a contraction ratio of 20.6:1. The cross-sections of the entrance and test section are square. The largest test section is 61 cm by 61 cm (24 in x 24 in) The reduction cones are so designed as to provide very low turbulence levels in the test section. Just ahead of the reduction cone is a set of twelve anti-turbulence screens. Both the reduction cone and the test sections are mounted on rollers to provide an easy means of interchanging these components. Downstream of the test section is the diffuser which is fixed into the wall of the laboratory. The diffuser decelerates the air and also gradually transforms the square contour to a circle. The impeller is driven by a variable speed electric motor. By varying the speed of the motor, the tunnel speed may reach a maximum of approximately 67.76 m/seconds or (150 mph). The test sections, which are 1.8 meters (1.6 feet) in length or which may be coupled in series to achieve a 3.6 meters (12 foot) length, have glass front panels, making smoke visualization possible. Smoke is generated by a device with allows kerosene to drip onto electrically heated filaments; the smoke is then funneled to a smoke rake. The rake has a filter bag and cooling coils which reduce the smoke temperature to approximately ambient before passing through the anti-turbulence screens and into the test section. Instrumentation for the tunnels includes force balances, LDV, hot-wire anemometry and pressure scanning systems. Current research involves the examination of delta wing aerodynamics and different aspects of vortex dynamics, low Reynolds number aerodynamics of low aspect ratio wings, fundamental studies of high lift systems, bluff body experiments and studies of boundary layer receptivity to free-stream turbulence as an indirect measurement of free-stream turbulence in cryogenic wind tunnels.
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