Control of cavity flow by upstream mass injection

Abstract

The purpose of this investigation was to use mass-injection ahead of the cavity t o control the shear flow across the cavity t o reduce or eliminate cavity oscillations. A brief review and analysis of cavity flow, shear layer flow and mass-injection is presented. The results of an experimental study performed at a nominal Mach number of 1.8 are provided. Significant attenuation of cavity oscillations was observed experimentally with upstream mass-injection. The thickening of the cavity shear layer alters its stability characteristics such that its preferred vortex roll-up frequency falls outside of the natural frequencies of the cavity. As a result of the experimental investigation, it is concluded that mass-injection is effective in significantly reducing or eliminating cavity oscillations. Cavity oscillation amplitude was reduced from about 174db (1.5psi) without mass-injection to 147db (0.07psi) at the blowing coefficient rate of 0.04.

Aeroacoustical Study of the TGV Pantograph Recess

“…Finally, solutions to reduce the radiated noise can mainly be achieved either by modifying the cavity geometry with passive devices (spoiler, ramp [5,8,12,15]) or by active control (mass injection [13]). …”

“…Although numerous of studies have been carried out recently on cavity grazing #ows (theoretical [1}3], experimental [4}11] or numerical [10,12,13]) over a wide range of Mach and Reynolds numbers with both laminar and turbulent boundary layers and over various length-to-depth ratios (¸/D), relatively few studies have dealt with the pantograph recess whose geometry (length¸, depth D and width =) gives ratios of¸/D'7)4 to 10)2 anḑ /='2)5 to 3)5. Its characteristics imply that it can be quali"ed as a closed (¸/D'7}8 [4,6]), three-dimensional (¸/='1 [11]) cavity.…”

POD based models of self-sustained oscillations in the flow past an open cavity

“…The (open-loop) introduction of flow disturbances has been studied both experimentally and numerically. 3,10,19,30,34 Significant reductions in sound pressure levels (around 20 dB) have been achieved through upstream mass injection 30 as well as piezoelectric flaps. 3 Closed-loop feedback control has also been studied, 3,15,21 and promises similar reductions in noise, but with much lower power input.…”

Effect of aft wall slope on cavity pressure oscillations in supersonic flows

“…Many experimental and computational studies have been directed toward improving the understanding of the physics of cavity flows and controlling their nature. Numerous methods (4)(5)(6)(7)(8)(9)(10)(11)(12) were studied and experimented over the years to control the oscillations in the supersonic cavity flows. Krishnamurthy (1) in one of the first observations found unsteady behaviour of rectangular cavities over a wide range of supersonic flows.…”