Receptivity of a Transitional Shock/Boundary-Layer Interaction to Shock Oscillations in Hypersonic Flow

The present work studies the complex dynamics of an oscillating shock impinging on a laminar/transitional supersonic boundary layer, with emphasis on the radiated post-shock waves and a coherent wave structure induced in the turbulent boundary layer (TBL) downstream of the separation bubble. Fully resolved direct numerical simulations (DNS) have been carried out at Mach 5, with imposed shock-oscillation frequency matching that predicted by earlier direct simulation Monte Carlo (DSMC) studies of the internal shock structure. Shock oscillations are found to produce a field of post-shock waves efficiently transmitted through the reattachment shock into the downstream TBL. The flow response consists of two-dimensional amplified planar waves propagating downstream with sustained amplitude. Increasing shock-oscillation amplitudes progressively enhance this phenomenon, while increasing frequencies, within the DSMC-predicted range, are found to promote a greater disturbance amplification, with amplitudes larger by 50% compared to lower frequencies. This indicates a high susceptibility of the wave transmission mechanism to the shock-oscillation frequencies. Conversely, the region between separation and reattachment shock is found to be sensitive to frequencies different from those of the shock oscillations. This previously unknown generation mechanism of a two-dimensional planar wave system within the TBL is altogether absent when the impinging shock is steady.