Effect of Screens and Pinhole Size on Measured Fluctuating Surface Pressures Using a Micro-Electro-Mechanical Microphone Array

Surface pressure measurements using microphone arrays are still challenging, especially in an automotive context with cruising speeds around Mach 0.1. The separated turbulent boundary layer excitation and the side mirror wake flow generate both acoustic and aerodynamic components, which have wavenumbers that differ by a factor of approximately 10. This calls for high spatial resolution measurements to fully resolve the wavenumber-frequency spectrum. In a previous publication [1], the authors reported a micro-electro-mechanical (MEMS) surface microphone array that successfully used wavenumber analysis to quantify acoustic versus turbulence loading. It was shown that the measured surface pressure at each microphone could be strongly influenced by self-noise induced by the microphone “packaging”, which can be attenuated with a suitable windscreen. This paper reports the results of wind tunnel tests to more accurately define the sensitivity of the MEMS microphone array with and without windscreens. The tests involved controlled attached boundary layer flow measurements in the anechoic wind tunnel at University of Sherbrooke. Different microphone sensing ports are evaluated as well as different microphone windscreens.