De-reverberation of a closed test section of a wind tunnel with a multi microphones cepstral method

Abstract

Today, the manufacturers of aircraft want to perform at the same time aeroacoustic and classical aerodynamic tests in the wind tunnels with closed test sections in order to reduce test duration and costs involved in new aircraft developments. However, this kind of wind tunnel is not optimal for acoustics testing because the measurements are often masked by background noise (i.e. noise generated by the wind tunnel flow mechanism) and reverberations on the walls without acoustic liner within the test section. This is a serious problem because these unwanted phenomena limit the accuracy of identification, and quantification of acoustic sources. The reduction of background noise can be obtained with subspace techniques or noise subtraction based on a noise reference measurement. Concerning the reduction of the contamination of the echoes, it can be achieved with an inverse filtering technique or with a single microphone cepstral method. A new approach is proposed in this study to remove the spurious effects of the echoes. It is based on multi microphones cepstral technique. This new technique has been successfully applied on numerical simulations, and experimental data. The theoretical developments of this method and the obtained results will be presented in the full paper. © 2013 Acoustical Society of America.