Comparison of cavity geometries for a microphone array in an open-jet wind-tunnel experiment

Conference paper (2020)

Authors

Colin VanDercreek Aircraft Noise and Climate Effects - Aerospace Engineering
R. Merino Martinez Aircraft Noise and Climate Effects - Aerospace Engineering
M. Snellen Aircraft Noise and Climate Effects - Aerospace Engineering
D. Ragni Wind Energy - Aerospace Engineering
D.G. Simons Aircraft Noise and Climate Effects - Aerospace Engineering
Research Group
Aircraft Noise and Climate Effects (Aerospace Engineering) (TU Delft)
Copyright: © 2020 Colin VanDercreek, R. Merino Martinez, M. Snellen, D. Ragni, D.G. Simons
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Published Date

2020

Language

English

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Faculty

Aerospace Engineering

Department

Control & Operations

Research Group

Aircraft Noise and Climate Effects

Abstract

This paper analyses the influence of microphone cavity geometry on beamforming measurements with a turbulent boundary layer present on the microphone array. A 16- microphone array was tested in the anechoic open-jet wind tunnel of the Delft University of Technology. The array was placed on a flat plate mounted flush with the exit nozzle of the wind tunnel. Microphones were installed in three different cavity geometries along with a flush mounted microphone array which was used as a baseline for comparison. The geometries include a chamfered-cylindrical hard-plastic cavity, a chamfered-cylindrical cavity made of melamine foam, and a chamfered-cylindrical cavity with star-shaped protrusions, also made of melamine. The recessed cavities were covered with a 0.026 mm gauge steelwire cloth. A speaker emitting white noise outside of the flow was employed as a sound source. Different flow velocities at the same sound power level for the speaker (and hence different signal-to-noise ratios) were studied. The results obtained with the three cavity geometries are compared with the flush-mounted case in terms of the quality of the acoustic source maps (location and strength of the sound source). The signal-to-noise ratio of the beamforming measurements increased by as much as 30 dB by placing microphones within a conical cavity with melamine foam walls when compared to the flush mounted case.