Effects of resistive windscreens and foam inserts on the acoustic response of an in-flow phased microphone array

摘要

Recent wind tunnel and anechoic chamber research studies of in-flow phased microphone arrays at NASA's Ames, Glenn, and Langley Research Centers have been conducted to characterize the effects of windscreens and cavity foam inserts on the suppression of low-frequency flow noise and modification of the broadband frequency response. It is shown that the windscreen correction factor, defined as the ratio of array responses without-to-with the windscreen, for arbitrary reception angles can be accurately extrapolated from the broadside correction spectrum, and the effects of convection on the directional response of the windscreen can be corrected with conventional expressions for effects of convection and refraction on source emission angle. The steady flow resistances of various stainless steel and Kevlar cloth screens were measured from 0.1 to 1.4 m/s. A simple 1-D acoustic model for the normal incidence windscreen correction was derived from published expressions of the cavity impedance and reflection coefficient. The predictions from the model compared well with measurements of the screen samples in an impedance tube, and showed similar trend compared with measurements of windscreen corrections in an anechoic chamber. The results will be used to develop calibration and correction methods for in-flow arrays that use windscreens to suppress low-frequency flow noise.