Disturbance evolution in compressible boundary layers on impermeable and porous surfaces under external pressure gradient

摘要

This study continues a cycle of investigations aiming at the modeling of passive methods for controlling flow regimes in compressible boundary layers. The effect of the streamwise pressure gradient on the evolution of different-in-nature disturbances developing on rigid and porous surfaces is considered. On rigid surfaces for a small supersonic Mach number M = 2 an increase in the external pressure leads to an earlier laminar-turbulent flow transition; contrariwise, a decrease in the pressure results in a transition delay. For the high Mach number M = 5.35 acoustic disturbances show a very strong dependence on the sign and the value of the external gradient; at a favorable gradient their critical Reynolds numbers can become even smaller than those of vortex disturbances, whereas at an adverse pressure gradient the boundary layer is destabilized immediately on the leading edge. For vortical-in-nature fluctuations an interesting phenomenon of transition reverse is detected. On porous surfaces these tendencies can either enhance or decay in accordance with the destabilization of the vortex modes and the stabilization of the acoustic ones.