Imaging aeroacoustic sources in a wind-tunnel with a massive array of MEMS microphones

This presentation deals with the identification of aeroacoustic sources in the open section of an anechoic wind-tunnel by using a three-dimensional (3D) array of 256 microphones. The antenna is made of three perpendicular planar arrays enclosing the test-section, and the microphones are digital MEMS microphones. The data processing is based on the beamforming technique associated with a deconvolution method (CLEAN) developed in 3D to improve the spatial resolution. Some preliminary tests with a well-controlled artificial source validate the set-up and the calibration procedure. Some measurements are carried out with aeroacoustic sources generated by the interaction of obstacles with the wind-tunnel flow. The academic case of a cylinder emitting aeolian tones is first considered. A more complex case is then considered with a symmetric wall-mounted NACA airfoil. The different sources (trailing edge noise, tip noise, and junction noise) are successfully identified in a 3D volume in terms of position. The study demonstrates that aeroacoustic source identification is achievable in three dimensions by using a massive array of very cheap MEMS microphones when associated to appropriate data processing techniques.