Design and Testing of a Low Self-Noise Aerodynamic Microphone Forebody

摘要

An extensiv study on the origin and improvement of the self-noise characteristics211u001eof aerodynamic microphone forebodies (AMF) was carried out. Theoretical analysis 211u001eof the pressure distribution and the boundary layer development along the outer 211u001esurface of the forebody revealed that the position of the screen and the 211u001eroughness height may be extremely critical. Based on this knowledge, an AMF with 211u001ea more stable boundary layer at the screen position was developed. This AMF 211u001eexhibited a better self-noise behavior up to 80 m/s but only for small flow 211u001eangles. A further series of experiments with a modular AMF assembly showed that 211u001ethe geometric details of the screen affect this behavior, and led to the design 211u001eof an AMF with a special perforated plate as a screen and a different number and 211u001egeometry of the cavity holes. The flow resistance of this perforated plate was 211u001eselected on its capability to subdue cavity shear flow oscillations over a wide 211u001eangular range while the loss of sensitivity of the AMF is kept to a minimum. the 211u001einfluence on the free-field response of the improved AMF was determined in an 211u001eanechoic facility.