Effect of Scaled Angle on Unsteadiness Characteristics of Large Separation Bubbles in High Speed Flows

Abstract In this work, high-speed flows at moderate Reynolds numbers over compression ramps with large scaled angles were computed using the Direct Simulation Monte Carlo (DSMC) method. The free-stream conditions and ramp angles were selected to ensure that the resulting scaled angles were large, leading to correspondingly large separation bubbles. The study revealed that once the separation bubble reached a certain size, further decreasing the wall temperature and increasing the free-stream speed and physical ramp angle destabilized the flow, and resulted in the formation of secondary recirculation regions. Moreover, configurations that had secondary recirculation regions were found to exhibit unsteady behavior. This unsteadiness in the near-reattachment region was particularly pronounced across all cases.