Stabilization of disturbances in a supersonic boundary layer using a compliant coating

The effect of a compliant coating (thin-film) over a porous surface on the stability of a supersonic (M = 2) boundary layer on a flat plate to disturbances of the first mode of instability under the conditions of experiments in the T-325 wind tunnel was calculated using linear stability theory. The calculations showed that a porous coating with a thin-film membrane on the surface can stabilize the boundary layer at Mach number M = 2 at the most amplifying frequency on an impermeable solid plate. The dependences of the spatial amplification rates of disturbances on a number of factors were established. Nonmonotonic (with minima) dependences of these growth rates on film tension, pore radius, porous coating depth, and porosity were obtained. The spatial growth rates of disturbances decrease with decreasing film thickness and the ratio of the gas pressure inside the pores to the static pressure in the boundary layer. It was found that stabilization of a supersonic (M = 2) boundary layer relative to the case of a smooth impermeable plate can occur only with a film thickness of less than 18 nm.