Identification of sources of sound in low mach number flows by the use of flow field eigenmodes

Authors: Kierkegaard, A. K., Efraimsson, G, Hoepffner, J.P.J., Åkervik, E.Å., Henningson, D.S.H., Åbom, M. Å.
Document Type: Conference
Pubstate: Published
Journal: Proceedings of 13th international congress on sound and vibrations.
Year: 2006


We present a method to study sound generation processes in low Mach Number flows. Instead of the full flow field obtained from e.g. a DNS, we consider a base flow together with a time-dependent perturbation, where the perturbation satisfy the Navier-Stokes equations linearized around the base-flow. In a reduced model the perturbation is approximated by a linear combination of the eigenmodes of a corresponding eigenvalue problem. The behavior in time is determined by the corresponding eigenvalues. Curle`s equation is used to calculate the acoustic field. By studying the source terms in Curle`s equation, it is possible to identify mechanisms for 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 twodimensional flow over a cavity with smoothed corners. Results of acoustic pressure in the far field and source strengths for different superpositions of eigenmodes are presented.