Three-dimensional identification of flow-induced noise sources with a tunnel-shaped array of MEMS microphones

Abstract This paper deals with the development of a three-dimensional (3D) array for imaging aeraocoustic sources in the open section of an anechoic wind-tunnel, together with the associated signal processing techniques, and presents an application to the case of a wall-mounted airfoil in a flow. The 3D antenna is made of 256 digital Micro ElectroMechanical Systems (MEMS) microphones, arranged into three nearly perpendicular planar arrays enclosing the test section, the lower part of the flow being bounded by a rigid planar surface. The source under consideration is a wall-mounted NACA 0012 airfoil located in the wind-tunnel flow at a chord-based Reynolds number of 5.33 × 105 for angles of attack at 0°, 4°, 10° and 20°, generating several broadband sources of noise. A configuration with two wall-mounted airfoils in a flow using a similar large array system is also studied. The data processing is based on the beamforming technique associated to a deconvolution method (CLEAN-SC) developed in 3D and to a dipolar radiation model. The flow effects on propagation are taken into account in the beamforming technique by using the Amiet's method in terms of angle correction. The application to the airfoil demonstrates that the performances of the 3D source localization method are excellent for the wall-mounted airfoil, due to the high number of microphones and to the “tunnel” geometry allowing to surround the sources in the flow. The different sources of noise that are to be expected are accurately identified in the third-octave bands under investigation, and are in good agreement with experimental results published in the literature. The presented results prove that a tunnel-type array including several hundreds of microphones associated to an appropriate array processing technique performs very well for studying in 3D complex aeroacoustic sources, and that cheap MEMS microphones are good candidates for measuring the sound radiation efficiently.