Scaling Laws in Automotive Aeroacoustics

Scaling laws - for example the variation of sound pressure with wind speed - are a key to the physical understanding of aeroacoustic phenomena. Aeroacoustics in Automotive applications differs from other fields of aeroacoustics: It is limited to low Mach numbers, the flow field is dominated by separated flows and the radiation into the far field is typically not of primary interest. On the other hand there are of course many common problems and findings shared with other fields in aeroacoustics. Therefore it is important to identify common areas with other, probably more advanced directions in aeroacoustics. But this has to be done without forgetting the practical demands of automotive application.

Main sources for interior wind noise in vehicles are leakage noise, cavity noise and the noise generated by separated flows at the outer surface. All three of these noise sources will be investigated in this paper. Of special interest will be the dependence on the wind velocity. It will be shown that three different exponents (U⁴, U⁶ and U⁸), corresponding in aeroacoustics to monopole, dipole and quadrupole noise, can be present in a single source.