Reverberation cancellation in a closed test section of a wind tunnel using a multi-microphone cesptral method

Abstract

Abstract Nowadays, although aerodynamic data are still primarily sought after during wind tunnel tests, reliable acoustic measurements also become a priority for aircraft designers. In order to gather both kinds of data, aerodynamic and acoustic tests are carried out simultaneously under the same closed test section. This solution has two major drawbacks: the acoustic signals delivered by microphones may be corrupted by the boundary layer expanding on the wind tunnel walls and by the reverberant noise originating from reflective surfaces. Technological solutions can be deployed to reduce the corruption of the signals by the wind tunnel background noise. Methods based on the power cepstrum can be used to reduce reverberation effects by removing the quefrencies due to the echoes in the cepstral domain. The difficulty of the cleaning operation is to separate the quefrencies of the echoes from those of the echo-free signal. The proposed solution overcomes this difficulty with a multiple microphone power cepstrum method. It allows us to estimate, in a blind way, the quefrencies responsible for the corruption by echoes to carry out the reverberation cancellation operation. This method was successfully applied on numerical simulations and experiments conducted in the closed test section of a wind tunnel without and with flow noise.