An Evaluation of Factors Affecting the Flow Quality in Wind Tunnels,
COMPLERE INC PALO ALTO CA
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Tests have been conducted in a number of NASA wind tunnels to measure disturbance levels and spectra in their respective settling chambers, test sections, and diffusers to determine the sources of these disturbances. Results indicate that properly designed and located second minimums in transonic tunnels prevent pressure fluctuations originating at struts and in diffusers from propagating upstream into the test section. The installation in or upstream of the settling chamber of carefully selected screens, honeycomb, and acoustic baffles could further reduce test section turbulence levels and scales without significant pressure losses. The performance of these modifications will be strongly influenced by tunnel geometry and its influence on the mean flow around the circuit.