By Thomas J. Mueller, Christopher S. Allen, William K. Blake, Robert P. Dougherty, Denis Lynch, Paul T. Soderman, James R. Underbrink
The objective of aeroacoustic measurements is to supply a foundation for assessing mechanisms of noise iteration, and to advance tools of lowering noise to extra applicable degrees. in spite of the fact that, the measurements themselves are complicated, and require a deep knowing of the experimental facility applied (such as a wind tunnel), size instrumentation, and knowledge research options.
In this quantity contemporary advances within the dimension and realizing of aerodynamically generated sound are offered through leaders within the improvement of recent innovations during this box. either easy and utilized difficulties are lined in detail.
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Additional info for Aeroacoustic Measurements
It is also difficult to measure sound directly upstream and downstream of a wind tunnel model because of the wakes from the microphone strut and model. Generally, the sound should be mapped in a streamwise plane from 20° to 160° as measured from the noise source, 0° being upstream. Ten-degree increments are sufficient except in regions of rapid directivity change such as in the peak jet noise radiation direction. The added benefit of such a mapping is that the data can be used to simulate an aircraft flyby as discussed below.
The average auto-power spectra of the array microphones flush-mounted and recessed are plotted. No array processing was done, so the curves represent the noise reduction a single microphone would experience. Wind Tunnel Background Noise Including Flow-Induced Noise 21 porous cloth microphone holder b Fig. 13. (a) Recessed microphone array in wind tunnel wall with circular Kevlar 124® cover and (b) microphone mounting details (Jaeger et al. 7-mm deep recess. Below 2 kHz, the measured noise agrees with the prediction.
Below 5 kHz, the reduction can be attributed primarily to a reduction in flow turbulence. From 5 kHz to 12 kHz, the reduction is probably related to the thinner floor boundary layer and improved sound absorption at all walls. -------~----------~----------~--. - B&K - previous wall lining FITE - previous wall lining 11 0 + ............................................ ; . . . . ::i. o N ~ 100 a:l -c c: ~ 90+······································ ,............................................................................
Aeroacoustic Measurements by Thomas J. Mueller, Christopher S. Allen, William K. Blake, Robert P. Dougherty, Denis Lynch, Paul T. Soderman, James R. Underbrink
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