Abstract

A consortium of German automotive manufacturers investigated the noise generated by the air flow around the A-pillar and the side mirror of a generic vehicle model and the noise transmission through the front side window. The DLR was responsible for the optimization of the microphone distribution on the side window and the post processing to distinguish between acoustic and hydrodynamic pressure fluctuations. The distribution of the microphones within the side window was optimized to increase ratio of the main lobe to side lobes with the limited number of microphones and space at hand. A loudspeaker was placed in the side mirror in order to determine the array performance. Wavenumber space was chosen for display as it reveals different characteristics of the pressure fluctuations: acoustic components of the pressure propagate at the speed of sound. They appear inside the acoustic Mach-ellipse. Pressure fluctuations outside this ellipse are regarded as hydrodynamic fluctuations. Their energy is mainly concentrated in the “convective” ridge. Its position represents the convective flow speed.

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