Control of shock wave/boundary layer interactions in a supersonic air intake using a modified backward-facing step

The safe operation and performance of a mixed compression air intake critically depend on the nature of shock wave/boundary layer interactions (SBLIs). The interaction between the ramp boundary layer and the cowl shock at the ramp–isolator junction plays a key role. In this experimental study, a modified backward-facing step called “notch” is used at the ramp–isolator junction to control the SBLI in a rectangular intake at Mach 3. The unstart and performance characteristics are evaluated and compared with the baseline, “faceted” configuration. The intake was unstarted by varying the back-pressure using a choke flap located at the exit in a quasi-steady manner. The surface and rake pressure measurements in addition to the shadowgraph and oil flow visualizations were taken to characterize the effect of flow control. The results showed that the notch anchors the separation bubble at the ramp–isolator junction and helps mitigate the strength of SBLI. The notched intake static pressures are relatively lower as compared to the baseline configuration suggesting reduced severity of structural loads. The floor boundary layer is energized by the notch leading to better efficiency and flow uniformity. There is an increase in the margin of unstart due to the presence of the notch by 7–10%.