Phased microphone arrays have become a well-established tool for performing aeroacoustic measurements in wind tunnels (both open-jet and closed-section), flying aircraft, and engine test beds. This paper provides a review of the most well-known and state-of-the-art acoustic imaging methods and recommendations on when to use them. Several exemplary results showing the performance of most methods in aeroacoustic applications are included. This manuscript provides a general introduction to aeroacoustic measurements for non-experienced microphone-array users as well as a broad overview for general aeroacoustic experts.

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A review of acoustic imaging methods using phased microphone arrays

Acoustic beamforming for noise source localization - Reviews, methodology and applications

A method is described for the location of moving sources by a microphone array. This method can be applied to out-of-flow measurements in an open jet wind tunnel. For that purpose, an expression is derived for the pressure field of a moving monopole in a uniform flow. It is argued that the open jet shear layer does not form a serious obstacle. A technique is described for reconstruction of power spectra with high signal/noise ratio. The method was implemented for rotating sources, resulting in the computer program ROSI ("Rotating Source Identifier"). Applications of ROSI are given for rotating whistles, blades of a helicopter in hover and wind turbine blades. The test with the rotating whistles demonstrated convincingly the capability to reconstruct the emitted sound. On the helicopter blades, rotating broadband noise sources were made clearly visible. On the wind turbine blades, noise emitted from the leading and trailing edge could be distinguished well.
Paper presented at the 7th AIAA/CEAS Aeroacoustics Conference, Maastricht, The Netherlands, 28-30 May 2001.

A.J. Bradley

Papers

De-Dopplerization and acoustic imaging of aircraft flyover noise measurements