Theoretical modeling and optimization of porous coating for hypersonic laminar flow control

A theoretical model is developed to describe the acoustic characteristics of plane ultrasonic acoustic waves impinging on a porous coating, namely, a rigid surface periodically corrugated with subwavelength grooves (two-dimensional cavities). The proposed model takes into account the high-order diffracted modes, and therefore incorporates mutual coupling among neighboring cavities. The model predicts a reflection frequency consistent with the numerical results and reproduces a couplingmode induced by interactions between waves scattered from adjacent cavities. With this model, the cavity geometry parameters are optimized to achieve the minimum reflection coefficient. The result shows that the Mack second mode is strongly suppressed and that the maximum fluctuating pressure decreases by about 88% upon using the optimized porous coating in a Mach 6 flat-plate flow.