Wavenumber-frequency analysis of the wall pressure fluctuations in the wake of a car side mirror

The numerical prediction of the wind noise in a car cabin requires distinguishing between the aerodynamic and the acoustic components of the wall pressure fluctuations loading the car side windows. It is theoretically possible to separate them using a time and space Fourier transform. Nevertheless the acoustic component is much smaller in amplitude than the aerodynamic one, and may be obscured by the numerical noise. We use in this work a direct noise computation code which can solve the full compressible three dimensional Navier-Stokes equations with highly accurate space and time algorithm. This code is able to capture the acoustic wall pressure fluctuations and to deal with complex geometry. We focus in this paper on the case of a car side mirror over a flat plate that has also been experimentally studied in a wind tunnel. The good agreement between the computed and the measured wall pressure fluctuations in the wake of the mirror validates the numerical predictions and allows the post processing of the simulated data: The wavenumberfrequency diagram of the power spectral density shows clearly two distinct cones corresponding to the acoustic and the aerodynamic components of the wall pressure fluctuations.