  The physics of shock-boundary layer interactions (SBLIs) in a supersonic
turbine cascade at Mach 2.0 and Reynolds number 395,000, based on the axial
chord, is investigated through a wall-resolved large eddy simulation. Special
attention is given to the characterization of the low-frequency dynamics of the
separation bubbles using flow visualization, spectral analysis, space-time
cross correlations, and flow modal decomposition. The mean flowfield shows
different shock structures formed on both sides of the airfoil. On the suction
side, an oblique shock impinges on the turbulent boundary layer, whereas a Mach
reflection interacts with the pressure side boundary layer. The interactions
taking place in the present turbine cascade show similarities and discrepancies
with respect to more canonical cases. For example, the characteristic
frequencies of the shock/bubble motions are comparable to those described in
the literature of canonical cases. However, the suction side bubble leads to
compression waves that do not coalesce into a separation shock, and a thin
bubble forms on the pressure side despite the strong normal shock from the Mach
reflection. Instantaneous flow visualizations illustrate elongated streamwise
structures on the incoming boundary layers and their interactions with the
shocks and separation bubbles. The space-time cross-correlations reveal that
the near-wall streaks drive the motion of the suction side separation bubble,
which in turn promotes oscillations of the reattachment shock and shear layer
flapping. Organized motions in the SBLIs and their corresponding characteristic
frequencies and spatial support are identified using proper orthogonal
decomposition.
