Phase calibration of in-duct axial microphone arrays

Lowis, C.R. and Joseph, P.F. (2009) Phase calibration of in-duct axial microphone arrays. In Proceedings of the15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference). American Institute of Aeronautics and Astronautics..

Abstract

In-duct microphone arrays are used in experimental test facilities to understand the generation of noise by aeroengine componants such as fan-blades. A typical microphone array used to perform modal analysis, for example, is a linear array of wall-mounted microphones. Accurate results can only be obtained if the microphone array is well calibrated for both magnitude and phase. As in-situ calibration is often impossible the microphones must therefore be calibrated outside of the duct. This is unsatisfactory as changes in the phase response that result from mounting the microphones in the duct wall after calibration, where they are exposed to flow and temperature effects, and the effects of the microphone mounting are not accounted for. This paper presents a method to calibrate the microphones in-situ using properties of the broadband noise generated, for example, by rotating fan blades. The technique allows the relative phase difference between individual microphones to be determined. The technique is validated using experimental data obtained from a laboratory scale no-flow rig.

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