EFFECTS OF DIFFERENT MODES ON SHOCK WAVE/TRANSITIONAL BOUNDARY LAYER INTERACTIONS IN A HIGH-SPEED FLOW

Shock wave/transitional boundary layer interaction, due to its flow complexity and severe mechanical/thermal damage, is a critical challenge in a high-speed flow. Wall-resolved implicit large eddy simulations were employed to investigate the shock/transitional boundary layer interaction at Ma = 6, considering two types of transition mechanisms. The characteristics of friction and heat flux are analyzed, differences of which between the two cases are scrutinized. Additionally, the evolution of the unstable modes is investigated to reveal the reasons for differences in aerodynamic and thermal characteristics. The current results demonstrate that the shock wave/transitional boundary layer interaction can significantly amplify the small-amplitude waves in the early stage of the boundary layer transition, thus accelerating the boundary layer transition. However, it does not alter the dominant transition mechanism. Results from dynamic mode decomposition also support this conclusion. Furthermore, compared to the natural transition, this interaction significantly enhances the peak of the skin friction and heat flux. For the shock wave/transitional boundary layer interaction dominated by the second modes, the analysis of the vortical structures and disturbance evolution indicates that the boundary layer transition is still driven by the fundamental resonance mechanism. Nevertheless, the skin friction coefficient and Stanton number undergo two distinct growth phases and reach a relatively higher level due to the boundary layer reattachment and vortex breakdown. For the interaction dominated by a pair of optimal modes, the boundary layer transition is still primarily governed by the oblique-mode resonance. In contrast, the boundary layer transition within the interaction is at the weakly nonlinear stage, and the vortices breakdown is not completely yet. Therefore, the skin friction and Stanton number only experience one-time growth, resulting in overall smaller peaks. The differences in peak skin friction and heat flux between these two cases are linked to the transition mechanism and state of the transitional boundary layer in the region of the interaction. These findings could act as useful guidelines for the design of aircraft aerodynamic configurations and thermal protection systems.