Experimental study of supersonic flow over cavity with aft wall offset and cavity floor injection

Experimental studies were conducted at Mach 1.71 supersonic flow over open cavity to find the best configuration of combined passive (aft wall offset) and active methods (cavity floor injection) to optimize the noise suppression. Cavity of length to depth ratio 3 with 0%, 5% and 10% aft wall offset were analyzed with the combined effect of 2 bar, 4 bar and 6 bar injection pressures, injected from locations of 25%, 50% and 75% of cavity length from the front wall. Experimental methodology includes instantaneous schlieren visualization and unsteady pressure measurements. In all the schlieren images, the presence of shear layer and various cavity flow features are clearly visible. Suppression in tonal amplitude for increase in offset and injection pressure is observed for various injection locations. Injection location at 75% cavity length from front wall was found to provide the maximum suppression. Spectrogram plots clearly indicate the redistribution of energy among tones and broadband noises. Increase in the number of tones is observed for higher injection pressure and aft wall offset combination. Nature of acoustic wave is confirmed from correlation and coherence plot. Over All Sound Pressure Level (OASPL) and normalized mean pressure plot are used to perform comparative study for various configurations.