Flow Instability in a Hypersonic Boundary Layer Behind a Propagating Shock Wave

Instability of a boundary layer developed behind a propagating shock wave is theoretically and numerically investigated. A numerical simulation of the boundary layer behind the propagating shock wave is conducted using a shock stationary frame method, efficiently solving the flow field around the propagating shock wave in an inertial frame where the shock wave seems to be stationary. An analysis of a linear stability theory based on the averaged flow field obtained by the numerical simulation finds that a wall cooling effect of an isothermal wall makes the boundary layer unstable. Moreover, an artificial disturbance is introduced on the wall in the numerical simulation to investigate the growth of the disturbance. The introduced disturbance grows downstream as it supports the analysis result of the linear stability theory. It is suggested that this flow instability causes the laminar-turbulent transition in the boundary layer behind the propagating shock wave.