Experimental study of synthetic aperture microphone array on rotor blade noise.

Abstract

Recent development of signal processing technologies has encouraged the aero-acousticians to implement the state-of-the-art sensors and data acquisition devices. They sometimes cost too much; however, especially for the academic arenas, the efforts of reducing the expense of integrating a system and increasing performance of phased array have initiated the idea of designing the synthetic aperture microphone array. The application of beamforming technique in localizing rotor blade noise and the use of synthetic aperture array in wind tunnel testing are presented. To apply the synthetic aperture beamforming on rotating objects, three steps should be considered. The first step is to restore the original acoustic waveform radiated from a rotating sound source. The second step is to synthesize independent array measurement data by correcting phase information of the received acoustic signals. Finally, the beamformer calculates the power on each point of grid in the space. The paper describes the details of deploying the synthetic aperture microphone array and the data reduction methods associated with acoustic measurement in wind tunnel. The comparisons of various patterns of synthetic aperture array are made. The beampower maps for rotor blade noise of various flight conditions are presented.