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Helmholtz-resonators are discussed in technical acoustics normally in conjunction with attenuation of sound, not with amplification or even production of sound. On the other hand everybody knows the sound produced by a bottle, when someone blows over the orifice. During the investigation of the sound produced in body gaps it was found that the underlying flow physics are closely related to the Helmholtz-resonator. But different from the typical Helmholtz-resonator generated noise – as for example the blown bottle or, from the automotive world, the sun roof buffeting – there is no fluid resonance involved in the process. For body gaps the random pressure fluctuation of the turbulent boundary layer is sufficient to excite the acoustic resonance in the cavity. The sound generation is characterized by a continuous rise in sound pressure level with increasing velocity, the rise is proportional to U with varying exponents.

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.