Control of cavity flow oscillation through leading edge flow modification

Abstract

The effects of a leading edge ramp and mass injection on supersonic cavity flow oscillations are investigated at Mach 1.5 and 2.5, through solutions of Reynolds-averaged Navier-Stokes equations with the effect of turbulence modelled by a two-equation k — u model. The flow is found to undergo a coupled motion of shear layer flapping in transverse direction and vortex convection in streamwise direction due to non-linear propagation effects, which leads to two different responses with the introduction of a leading edge ramp at Mach 1.5 and 2.5. At Mach 1.5, a strong flapping motion leads to nearly similar Strouhal numbers and sound pressure levels in the cavity compared with a baseline case. The roll-up of the shear layer produces convective vortices, leading to enhanced pressure fluctuations on the downstream surface. At Mach 2.5, a weak shear layer instability produces a reduction in sound pressure level, and the increased distance between the edge of the ramp and the trailing edge produces a reduction in the Strouhal number. When mass injection is introduced, a passive pressure response is observed, leading to local vorticity production and vortex shedding. The flow mechanism remains the same at both Mach numbers, with a weak sitting vortex near the trailing edge. The study has identified an optimal mass injection pressure ratio for flow control.