Conditional Analysis of Shock-Induced Flow Separation Events in a Supersonic Turbine

We perform a conditional analysis to examine the differences between large and small bubble states in a shock–boundary layer interaction over the convex surface of a supersonic turbine at Mach 2.0 and Reynolds number 395,000. The analysis focuses on mean flow and turbulence quantities. The results indicate that large bubbles are associated with a higher wall pressure upstream of the incident shock, caused by stronger flow compression, whereas small bubbles exhibit increased wall pressure downstream of the incident shock, attributed to earlier flow reattachment. Regarding the turbulence quantities, small bubble events display higher values of tangential Reynolds stress upstream of the incident shock compared to large bubble events, because of the presence of near-wall streaks. These coherent structures are typically accompanied by streamwise vortices, which promote intense fluid mixing and lead to increased wall-normal and spanwise Reynolds stress components. Consequently, turbulent kinetic energy is also higher for small bubble events. This elevated turbulent activity results in larger fluctuations in wall pressure and skin-friction coefficient along the separation region.