Noise reduction in cavity flow by addition of porous media

Self-sustained oscillation and the sound radiation of flow over an open cavity is of great importance in nature and industry. Influences of filled porous media in the cavity are investigated numerically by using a lattice Boltzmann method in two-dimensional space. It is shown that the outcomes of the porous patch depend on the location of the patch and the original flow mode, namely shear layer (SL) and wake mode (WM). For SL flow, the porous patch either damps the vortical flow or suppresses the generation of the secondary vortex sheet on the wall. The later effect destabilizes the SL. Consequently, the radiated sound is reduced as the patch is on the trailing edge, and increased with porous patch on the floor, respectively. For flow in WM, a transition from WM to SL mode is found when the porous ctherefore, the WM flow is not sustained. On the other hand, the porous patch on the trailing edge slightly weakens the sound due to dissipation. The study shows that assembling of porous media in the flow field decreases the radiated sound level only if it is done carefully.