Effect of porous surface on the flat plate self-noise

In this study, the effect of porous surface on the turbulent noise generated by a blunt trailing-edge of a flat plate is investigated. The three-dimensional turbulent flow over the flat plate (Re_c=1. 3×10⁵ and M=0.06) is computed by incompressible large eddy simulation (LES) based on the volume-averaged Navier-Stokes equations, while the acoustic field is calculated by the linearized perturbed compressible equations (LPCE) coupled with LES solutions. The porous surface is applied to a small, selected area near the trailing-edge, where the Kármán vortex shedding and eddy scattering produce dipole sounds. The computed results show that the trailing-edge with porosity ε=0.25 and permeability (normalized) K^*=0.01 yields a reduction of tonal peak by 13dB for zero angle of attack (α=0°), via breaking not only in the streamwise direction but also in the spanwise direction the spatial correlation of the wall pressure fluctuations (R_pp) near the trailing-edge. For the separated flow case (α=5°), the same configuration of the porous surface is found to weaken the pressure fluctuations at the trailing edge. It results in 3-10dB noise reduction over a wide range of frequency, via reducing the separated flow region over the upper surface of the plate.