Control of cavity flow by upstream mass-injection

The purpose of this study was to use mass-injection upstream of a cavity to control the shear flow across the cavity for reducing or eliminating cavity flow oscillations. Results of an experimental effort performed at a nominal Mach number of 1.8 and at unit Reynolds number of 17 x 10 6 per foot for a cavity with length-todepth (LID) ratio of 2.54 are presented. Baseline measurements were performed for various mass-injection rates for two rectangular injection distributions. Significant attenuation of cavity oscillations was observed with upstream mass-injection. This was attributed to the thickening of the cavity shear layer, which altered its instability characteristics, such that its preferred vortex roll-up frequency was shifted outside of the natural frequencies of the cavity. As a result of the experimental investigation, it was concluded that mass-injection is effective in significantly reducing or eliminating cavity oscillations. Cavity's peak oscillation amplitude was reduced from about 174 dB (1.5 psi) without mass-injection to 147 dB (0.07 psi) at the blowing coefficient rate of 0.04.