Interplay between streaks, vortices and separation bubble in shock-boundary layer interactions over a supersonic turbine airfoil

The shock-boundary layer interaction (SBLI) over the convex wall of a supersonic turbine airfoil is studied with a focus on extreme separation bubble events and the interplay between the bubble, streaks, and streamwise vortices. The present analysis is performed on a dataset computed by a wall-resolved large-eddy simulation (LES) of a supersonic turbine at Mach number 2.0 and Reynolds number of 395,000. Conditional analysis is used to study extreme bubble events. First, mean and turbulence statistics are computed to examine differences between expanding and contracting bubble states. Then, finite-time Lyapunov exponent calculations are used to understand the interactions between streaks and streamwise vortices along large and small separation bubble events. A deforming control volume methodology is applied to analyze the mass imbalance within the bubble and identify regions that are more susceptible to mass inflow and outflow. In events where the recirculation region is small, high-speed streaks penetrate the bubble, being accompanied by streamwise vortices that meander and induce intense fluid mixing and high turbulent kinetic energy. In contrast, during events with bubble expansion, high-speed streaks are advected over the separation region, with streamwise vortices appearing only downstream of the shock, resulting in minimal fluid mixing inside the bubble. The analysis of mass flux over the bubble surface reveals that during its contraction phase, mass flux out of the bubble occurs predominantly upstream of the incident shock because of high-speed streaks dragged towards the wall by the streamwise vortices. In the expansion phase, pronounced mass flux into the bubble is observed downstream of the shock, near reattachment, due to the interplay between streamwise vortices and low-momentum flow structures.