Acoustic perturbation equations based on flow decomposition via source filtering

A family of acoustic perturbation equations is derived for the simulation of flow-induced acoustic fields in time and space. The mean flow convection and refraction effects are part of the simulation of wave propagation. Using linearized acoustic perturbation equations the unbounded growth of hydrodynamic instabilities in critical mean flows is prevented completely. The perturbation equations are excited by source terms determined from a simulation of the compressible or the incompressible flow problem. Since the simulation of wave propagation contains the convection effects the computational domain of the flow simulation has to comprise only the significant acoustic source region. The acoustic perturbation equations are validated by computing a monopole source in a sheared mean flow, the sound generated due to a spinning vortex pair, and the sound generated by a cylinder in a crossflow.