Kierkegaard A., Efraimsson G., Hoepffner J., Åkervik E., Åbom M.

We will present a method to study sound generation processes in low Mach Number flows. For low Mach numbers it is plausible to let the flow field be governed by the incompressible Navier-Stokes equations. However, instead of the full flow field we consider a linearized flow field which has been decomposed into eigenmodes of a corresponding eigenvalue problem. The eigenmodes are defined on the whole domain. In a reduced model the flow field is represented by a linear combination of these eigenmodes. The behavior in time is determined by the eigenvalues of the corresponding eigenmodes. The aim is to identify sound generating structures in the flow. In order to evaluate the acoustic field, Curle's equation is used. By studying the source terms in Curle's equation separately, it is possible to identify mechanisms for different sources of sound. This makes it possible to study how the different sources of sound depend on different structures of the flow field. We apply the methodology on a two-dimensional flow over a cavity with smoothed corners. Results of acoustic pressure in the far field and source strengths for different superpositions of eigenmodes will be presented.