Flow structure of supersonic flow past backward-facing step with perpendicular injector

Flow structures of supersonic flow past a backward-facing step with perpendicular injector are numerically investigated under the perfect gas condition in two-dimensional space. The incoming main flow is Mach number 2.5 and the injection is sonic jet, located 24mm behind the step. A step height (0, 2, 3, 6mm) and dynamic pressure ratio of the jet flow to the main flow (0.0, 0.2, 0.4, 0.6, 0.8, 1.0) are examined in the calculations. When the injector is far enough for the main flow to recover supersonic, the injection is independent of the effect of the backward-facing step. However, the jet interacts with the recirculation behind the step, the recirculation region expands to the jet. Once the recirculation region expands, the height of the recirculation region is clocsely related with the dynamic pressure ratio. The expansion waves from the step corner change to the compression wave when the height of the recirculation region becomes higher than the step height. For the step height 6mm, the unsteady oscillation appears in the flowfields. The mechanism of the oscillation is numerically clarified in the simulations.