BEAMFORMING AND DECONVOLUTION FOR AERODYNAMIC SOUND SOURCES IN MOTION

Acoustic beamforming with microphone phased-arrays is a powerful method to investigate the noise emission of vehicles (aircraft, trains, cars, etc.) . Per definition, the aerodynamic sound sources appear when these vehicles are in motion. Some of the sources, like the highlift devices of aircraft, are distributed in space. The beamforming patterns are the result of a convolution between the sources and point spread functions, which depend on the array geometry and source position. The performance of a phased array is characterised by two parameters: i) the beamwidth on which depends the capacity to separate two sources close to each other, and ii) the level of the side-lobes which describes the dynamic range. In static applications (the source positions are fixed with respect to the microphone array) the source strength of distributed sources can be determined by deconvoluting the beamforming solution. Some issues arise when a deconvolution is applied to moving sources because the frequencies of the side-lobes are shifted with respect to the main lobe. An approximate method for the deconvolution of the beampattern of moving broadband sources is derived and it is shown with simulated data that solutions can be obtained with a reasonable accuracy and computing time.