Towards a generic non reflective characteristic boundary condition for aeroacoustic simulations
A blended zonal characteristic boundary condition is proposed following a quantitative investigation of the performance of several non reflective boundary conditions. Two test cases are considered that investigate the effects of acoustic and vortical plane waves impinging on the domain outflow region. A third test case investigates the effects of broadband turbulent flow impinging on a non reflective outflow boundary condition. From these studies, two non reflective boundary conditions based on a zonal characteristic method are found to provide a minimal acoustic response for impinging acoustic and vortical disturbances, respectively. These methods both make use of the transverse characteristic terms to improve performance, although each method uses a different inclusion of these terms. A final boundary condition is proposed that blends the performance of the two zonal characteristic methods. A blending function is used that switches the characteristic boundary condition smoothly between regions dominated by acoustic, or vortical, disturbances. The feasibility of this novel method is demonstrated on a test case where broadband turbulence impinges on a small section of an outflow region.