Analysis of shock-boundary layer interactions in a supersonic turbine cascade using LES.*

A wall-resolved large eddy simulation is employed to investigate the unsteadiness of shock-boundary layer interactions (SBLIs) in a supersonic turbine cascade at Mach 2.0 and Reynolds number 395,000, based on the inlet velocity and the axial chord. The low-frequency dynamics of the interaction, including the separation bubble, shear layer and shock waves, is characterized using flow visualization and spectral analysis. The mean flowfield displays different impinging shock structures through the turbine cascade. On the suction side, an oblique shock interacts with the boundary layer, while a Mach reflection is formed on the pressure side. Instantaneous flow visualizations reveal the influence of upstream large-scale structures on the separation bubble motion. In addition, space-time correlations indicate that those structures drive the breathing of the separation bubble on the suction side. These correlations also suggest the existence of a π phase jump in the pressure fluctuations along the separation bubble. Despite some peculiarities regarding the curved wall of the turbine blade, the spectral analysis shows that the characteristic frequencies of the SBLIs are similar to those reported in impinging oblique shocks on flat plates, and compression-ramp interactions. However, some discrepancies are also reported, including the lack of a separation shock and the presence of low-frequency fluctuations on the reattachment location. The latter occurs due to the interaction between the streaky structures and the incident shock.