Susceptibility of shock-transitional-boundary-layer interaction to shock oscillations in hypersonic flow

The present study shows results from Direct Numerical Simulations (DNS) of a shock-transitional-boundary-layer interaction with imposed shock oscillations in a Mach 5 flow. The shock oscillation frequency matches the frequency pre- dicted by a previous Direct Simulation Monte Carlo (DSMC) study for the inner thermal nonequilibrium of the shock and the resulting induced shock oscillations, for the same Mach number. The transition process is induced in the upstream region by imposed disturbance waves at the wall representative of the most unstable modes, as predicted by a Linear Stability Theory (LST) study. An oblique shock corresponding to a 8-deg wedge angle is generated at the top boundary, which impinges on the boundary layer within the region of nonlinear breakdown. Simulations have been carried out both with and without oscillations imposed on the oblique shock, and for different amplitudes of the shock oscillations. It is found that the shock-boundary-layer interaction (SBLI) produces an acceleration of the transition process to a turbulent state downstream of the impingement point, and that the shock oscillations produce a quasi-2D wave-pattern mode modulation of the downstream turbulent boundary layer, which represents the footprint of the post-shock waves generated by the shock oscillations. Increasing amplitudes of the shock oscillations show a progres- sively enhanced modulation of the turbulent boundary layer, with higher amplitude wall pressure fluctuations. These, in turn, have a relevant effect on the time-averaged wall pres- sure profiles, with an increasing mean wall pressure in the downstream turbulent boundary layer at increasing shock oscillation amplitudes. The wall pressure fluctuation amplitudes are found to scale linearly with the shock oscillation amplitudes in the higher amplitude range, however at lower amplitudes a higher sensitivity of the wall response to a change in amplitude of the shock oscillations is observed, suggesting that the correlated effects on the flow features may be relevant also for relatively small amplitudes of the shock oscillations.