Simulations of shock wave/turbulent boundary layer interaction with upstream micro vortex generators

The streamwise breathing motion of the separation bubble, triggered by the shock wave/boundary layer interaction (SBLI) at large Mach number, is known to yield wall pressure and aerodynamic load fluctuations. Following the experiments by Wang et al. (2012), we aim to evaluate and understand how the introduction of microramp vortex generators (mVGs) upstream the interaction may reduce the amplitude of these fluctuations. We first perform a reference large-eddy simulation (LES) of the canonical situation when the interaction occurs between the turbulent boundary layer (TBL) over a flat plate at Mach number M=2.7 and Reynolds number Reθ=3600 and an incident oblique shock wave produced on an opposite wall. A high-resolution simulation is then performed including a rake of microramps protruding by 0.47δ in the TBL. The long time integration of the simulations allows to capture 52 and 32 low-frequency oscillations for the natural case and controlled SBLI, respectively. In the natural case, we retrieve the pressure fluctuations associated with the reflected shock foot motions at low-frequency characterized by StL=0.02−0.06. The controlled case reveals a complex interaction between the otherwise two-dimensional separation bubble and the array of hairpin vortices shed at a much higher frequency StL=2.4 by the mVGs rake. The effect on the map of averaged wall shear stress and on the pressure load fluctuations in the interaction zone is described, with a 20% and 9% reduction of the mean separated area and pressure load fluctuations, respectively. Furthermore, the controlled SBLI exhibits a new oscillating motion of the reflected shock foot, varying in the spanwise direction with a characteristic low-frequency of StL=0.1 in the wake of the mVGs and StL=0.05 in between.