Flow dynamics in a supersonic cavity with upstream expansion ramp: An experimental study

This study presents an experimental investigation of the dynamics within a supersonic cavity flow. Aft-wall slanted cavities with upstream expansion ramps (5°, 7.5°, and 10°), and vertical aft-wall offsets are investigated. High-speed schlieren imaging, unsteady pressure measurements, Proper Orthogonal Decomposition (POD) analysis, and Sound Pressure Level (SPL) spectra are employed to capture unsteady features and shock structures. Results indicate that upstream ramps induce bifurcated shock trains and increase flow unsteadiness due to shear layer impingement. However, introducing aft-wall offsets significantly reduces pressure oscillations and suppresses shock trains, improving flow stability. The study demonstrates that offset configurations are effective in controlling flow-induced unsteadiness and offer a passive strategy for enhancing structural safety in high-speed propulsion systems.