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The perforated walls of transonic wind tunnels create such intense noise that the fluctuating pressure measurements and other dynamic data acquired on aerospace models can be adversely influenced. For an aerospace vehicle in-flight, the dynamic environments, e.g., fluctuating pressures, cause structural vibrations and the vibration of avionics packages. The suppression of transonic wind-tunnel background noise has been the goal of many investigators over the years; nevertheless, high-amplitude noise levels still exist in many transonic wind tunnels. Some exploratory tests were recently performed in the transonic test section of the NASA Marshall Space Flight Center 14-in. wind tunnel to suppress the background noise. In these tests, the perforated walls of the test section were covered with fine wire screens. The screens eliminated the edge tones generated by the holes in the perforated walls and significantly reduced the tunnel background noise. The tunnel noise levels were reduced to such a degree by this simple modification at Mach numbers 0.75, 0.9,1.1,1.2, and 1.46 that the fluctuating pressure levels of a turbulent boundary layer could be measured on a 5 ° half-angle cone.

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