Overset LES with an acoustic relaxation term for sound source simulations

Abstract

A novel Overset LES approach in perturbation form is presented to provide adequate turbulent information for the description of aerodynamically induced noise, but at the same time keep the computational effort within reasonable limits as compared to DNS. Solving the perturbation equations on top of a steady base flow leads to a hybrid approach, where scale-resolving simulation is only performed in necessary regions. The procedure is carried out in two steps. After capturing sound sources via the aforementioned methodology, the sound propagation is predicted by employing the Acoustic Perturbation equations. An Acoustic Relaxation Term is introduced to suppress pressure based grid-to-grid oscillations leaving other modes untouched. Its damping characteristics has been shown to be favourably frequency selective. The Acoustic Relaxation Term is able to damp or excite acoustic waves and in that way it potentially enables the excitement of prescribed acoustics in the Acoustic Perturbation equations for future applications. The governing equations are presented as well as the subgrid scale model. This subgrid scale model is calibrated with decaying isotropic turbulence.