Control of cavity flow by upstream mass-injection

TLDR

The study aims to use upstream mass‑injection to control cavity shear flow and reduce or eliminate cavity flow oscillations. The experiment varied mass‑injection rates across two rectangular injection distributions, observing that increased shear‑layer thickness shifted the vortex roll‑up frequency away from the cavity’s natural frequencies. Experimental results at Mach 1.8 and Re = 17 × 10⁶ ft⁻¹ with LID = 2.54 showed that upstream mass‑injection significantly attenuated cavity oscillations, reducing peak amplitude from ~174 dB (1.5 psi) to 147 dB (0.07 psi) at a blowing coefficient of 0.04.

Abstract

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.