The interaction of a spatially transitional boundary layer flow at freestream Mach number M = 2.0 with an impinging oblique shock wave (β = 35.56) is studied by means of direct numerical simulation (DNS). High amplitude (5%) three-dimensional isotropic disturbances are superimposed on the laminar profile for a Reynolds number based on the boundary layer displacement thickness of Re δ*0 = 1000 at the inlet plane of the computational box. Under the selected flow conditions, the interaction of the boundary layers with the incident shock wave produces three-dimensional separation, thus inducing a shock system (reflected waves and expansion fan). Linear-stability theory and DNS indicate that Λ-shaped vortices are generated in the separated shear layer due to the most unstable oblique mode, which can trigger the breakdown mechanism around the reattachment line. Energy spectral density of the wall-pressure indicates broadband spectra that are observed in the experimental result on shock/turbulent boundary layer interaction.

Spatial direct numerical simulation results are presented for transitional/turbulent supersonic isothermal flat plate boundary layers at M = 2.0 and impinging shock wave-boundary layer interactions. The numerical results show the formation and development of three-dimensional vortical structures such as hairpin packets and streak-breakdown, and secondary and tertiary hairpins as well. These characteristic vortical structures create a significant fraction of the supersonic turbulent boundary layer structure. An incident shock wave impinging upon the transitional boundary layer with streaks and hairpins, and unsteady reflected waves from the mildly separation boundary layer are observed. Expansion waves after the impinging point and compression waves due to the boundary layer reattachment are also identified. Across the interacting shock, turbulence is enhanced with finer hairpins generated inside, and it undergoes a relaxation process to higher Reynolds turbulent boundary layers far downstream.