Prediction of Porous Trailing Edge Noise Reduction Using Acoustic Jump-Conditions at Porous Interfaces

Abstract

Reduction of noise generated at geometric edges can be achieved by replacing solid material with porous inlays. The acoustic benefit for airfoil trailing edge noise was experimentally found to yield a reduction in sound pressure level of approximately 6 dB. Numerical methods are of interest to find optimal properties of the porosity. A successful method of modeling porous materials is the Volume-Averaging approach. In prior simulations, the prediction of the sound reduction was comparable to measurements over a limited frequency range. This has been enhanced to obtain simulation results which show a better agreement with the experimental findings. At the interface between the free fluid and the porous parts jump conditions are required to model the interaction of the acoustic and flow quantities in these two regimes when it comes to nonhomogeneous materials. This paper presents the perturbation formulation of a set of jump conditions for Computational Aeroacoustics (CAA), already known from Computational Fluid Dynamics (CFD). For the numerical implementation, a high-order compact boundary scheme is derived. Furthermore, the description of complex anisotropic materials is pursued. IIn a hybrid two-step CAA/CFD procedure, the turbulence statistics from the corre- sponding solution of the Volume-Averaged Navier-Stokes-Equations (VANS) is used to trigger vortices generating turbulent-boundary-layer trailing-edge noise (TBL-TEN).