Direct Numerical Simulation of the Trailing Edge Noise on a Flat Plate and the Effect of Finlets

There are increasing needs for reduction of trailing-edge (TE) noise from airplane wings. Finlets are known to be effective in reducing TE noise. The generation mechanism of the TE noise from a flow past a flat plate with/without finlets is studied by direct numerical simulations (DNS). First, the flow field around an untreated flat plate was conducted at Mach number M=0.2. The corrected volume penalization (VP) method, one of the immersed boundary methods, was used to represent the flat plate. In this method, the rigid bodies are regarded as porous materials with small permeability. The appropriate value of the permeability was determined carefully by checking convergence of the surface pressure distribution on the flat plate. The distance between the trailing edge and the observation points of the sound pressure is comparable to the length of the flat plate. Thus, the properties of the pressure at the observation points were checked to see whether we can detect the sound pressure correctly. The propagation velocity of the pressure fluctuations determined by the correlation between different points coincided with the sound speed. This confirms that sound generation is captured, although there exist components other than the acoustic waves. The reduction effects of finlets will be also discussed.