Direct numerical calculation of cylinder aeroacoustics by large eddy simulation with hybrid non-reflective boundary

Abstract non-reflective boundary condition is required by aeroacoustic direct numerical simulation. The commonly used methods are characteristic-based and far-field-based non-reflecting boundaries, whose performance will be attenuated by nonlinear flows at the outlet. Large Eddy Simulation further directly computes the compressible flow noise of a cylinder at Mach number 0.4. The limitations of characteristic-based and far-field-based non-reflecting methods are discussed. The impact of numerical dissipation and viscosity diffusion of the damping layer on the radiated sound field and the near Stream field are investigated. The results indicated that the hybrid non-reflective boundary effectively absorbs the reflected sound waves, reduces the interference noise between the radiated waves and the echo waves in the watershed, and obtains a more reasonable dipole acoustic radiation feature. The echo waves from the outlet are reduced, and a more reliable dipole radiation pattern is obtained. More echo waves are absorbed by the multi-dimensional stretched grids in the damping layer, as acoustic waves propagate in multi-dimensions are better matched. However, the impacts of the hybrid non-reflective boundary on the cylinder’s near-field flows are negligible.