Systematic Comparison of Microphone Array Measurements in Open and Closed Wind Tunnels

Abstract

A systematic comparison between microphone array measurements in closed and open test sections of wind tunnels is presented. The study focuses on the beamforming accuracy in both wind tunnel types with respect to source position, relative and absolute levels of beamforming results and integrated spectra using two difierent sound sources. At flrst, an in-∞ow calibration sound source incorporated in an electromechanic driver and with known characteristics is used. This kind of source allows to investigate the in∞uence of the difierent ∞ow conditions on the sound propagation and their in∞uence on beamforming results. In the second part of the test a plate with various cavities serves as an aeroacoustic sound source. In both wind tunnels the same phased microphone array is used for the measurements, whereby the aim is to keep the experimental setup and conditions as identical as possible in both cases in order to be able to examine the test section-dependent efiects. The beamforming results of the two difierent sources, obtained from measurements in both test sections, show a high qualitative and quantitative agreement provided that the SNR is su‐ciently high enough. The wind tunnel dependent deviations of the integrated source spectra do not exceed 4.7 dB.