Simulation of Multigeometry Scattering Problems and the Radiation and Refraction of Acoustic Waves through a Shear Layer with Instability Waves Suppressed

The scattering of harmonic acoustic waves at multiple rigid cylinders is simulated applying a Chimera technique and a body-fitted grid approach. The Chimera technique uses a Cartesian background mesh in conjunction with body-fitted O-grids in the immediate vicinity of the solid surfaces to resolve the geometry. The body-fitted grid approach applies a multiblock topology with O-grids wrapping the cylinders while an H-type topology is used away from the cylinders that converges against a Cartesian mesh in the far field. Both grid approaches are compared using a similar far-field resolution of about seven points per wavelength. The refraction of acoustic waves in an unstable jet is simulated using a modification of the linearized Euler equations that can be proven to be stable for arbitrary mean flow fields. The simulations confirm the modified perturbation equations to suppress the excitation of unstable modes. The wave operator encoded in the perturbation equations is known to be exact for irrotational mean flows, that is, in the high-frequency limit of the Strouhal number based on frequency f and mean-flow vorticity ω0 tending to infinity. It is shown that even for a Strouhal numbers of O(1), the modified acoustic perturbation equations resolve mean flow refraction and scattering effects accurately. For the jet, larger differences to the reference solution appear, in particular, downstream of the harmonic source position due to the small Strouhal number in the jet shear layer.