Mega Array of Microphones for the Identification of Environmental aeroacoustic Sources – MAMIES

The sound environment is an important element of quality of life in urban and peri-urban areas. Among the various types of environmental noise, the aeroacoustic noise produced by the interaction of flows and obstacles can be an important source of annoyance. Theses noisy interactions are related to transport noise (landing aircraft, trains, etc.) but also to a more recent problem concerning the noise emitted by the facade elements of modern or renovated buildings. To identify and understand these sources of noise in order to reduce them, mock-ups or samples of obstacles in anechoic wind tunnel are often studied. Sound source imagery is a classic tool for such studies, obtained by using microphone arrays and data processing tools such as beamforming. These techniques are currently developed in very simplified propagation, flow and directivity hypotheses, in order to obtain an analysis that reduces to a two-dimensional vision of the phenomena. Thus, the aim of the MAMIES project is to develop innovative experimental techniques for the study, identification and three-dimensional (3D) imaging of this type of aeroacoustic source in the context of wind tunnel measurements, in configurations for which classical techniques fail: highly 3D configurations, complex and / or unsteady flows, presence of diffracting objects in the noise production zone, complex source directivity.

The originality of the project is based on two advances in the identification of environmental aeroacoustic noise: the development of a new generation microphone array (with more than 1,000 microphones) based on MEMS technology, combined with new treatment methods based on the principle of time reversal and associating measurements and numerical simulations. The MAMIES project brings together two partners: the PPRIME Institute (University of Poitiers) where experiments will be carried out in the wind tunnel, and the Jean-Rond d'Alembert Institute (Sorbonne University) where the antenna will be developed. The processing techniques and the production and analysis of the experimental data will be carried out jointly. The developed array will completely encompass the area of the flow containing the noise sources to be identified. Thanks to the large number of microphones the 3D sampling of the radiated acoustic field will give an optimal spatial resolution of the sources. The processing techniques will make it possible to discard the assumptions about the propagation medium because they will be based on a 3D numerical simulation whose input data will be the experimental data, but also the real geometry and flow. This approach will take into account an arbitrary flow, the presence of objects in the flow, and operate in the time domain, allowing the study of transient annoying phenomena from an auditory point of view (eg gust effects). Thus real progress is expected in the ability of analysis of sources of noise. Once the tool is completed and validated, experimental campaigns will be carried out in the wind tunnel, targeting two types of applications. The first concerns the aeroacoustic noise emitted by aircraft wings. A finite wall-mounted airfoil will be studied in depth, then the case of three interacting airfoils which provides a model for high-lifted wings producing a very complex aeroacoustic radiation. The second application concerns the noise of facade elements in modern architectural projects, first through interacting elementary objects, then through the study of real samples.