Low-Frequency Unsteadiness Mitigation Through Control Bumps in Shock/Boundary-Layer Interactions

Low-frequency unsteadiness in oblique shock wave/boundary-layer interactions drives intermittent separation and large wall-pressure loads. Direct numerical simulations are performed of a Mach 2 turbulent boundary layer impinged by a 12 deg oblique shock, and passive control is assessed through a shock control bump (SCB) designed from the baseline interaction. The uncontrolled configuration exhibits a pronounced breathing motion of the separation bubble, with dominant wall-pressure energy at StL ≈ 0.03–0.05. The nominal SCB confines separation to small localized regions, reduces wall-pressure fluctuations across the interaction, and suppresses the low-frequency component at the reflected-shock foot by shifting spectral energy toward StL ≈ 0.1–1. A secondary unsteadiness appears near the bump apex at higher frequencies, but it does not reintroduce large-scale oscillations. Placement-sensitivity simulations show that an upstream shift retains most of the low-frequency mitigation, whereas a downstream shift exacerbates separation and restores pronounced low-frequency peaks. The results support a physical mechanism in which the bump imposes a geometric constraint on the reflected shock and generates a mild compression followed by a local expansion, thereby reducing shock mobility and mitigating low-frequency unsteadiness.