Attenuation of cavity flow oscillation through leading edge flow control

The unsteady flows over a shallow rectangular cavity at Mach 1.5 and 2.5 ar e modified at the leading edge by using compression ramps, expansion surfac es, and mass injection. The study is performed through solutions of Short-t ime Reynolds-Averaged Navier-Stokes equations (TRANS) with turbulence model led by a two-equation k-omega model. When a compression ramp is introduced, two types of responses are observed: at Mach 1.5, a strong flapping motion leads to small changes in the frequency and sound pressure level in the ca vity compared with the baseline case of rectangular geometry. The roll-up o f the shear layer produces convective vortices, leading to enhanced pressur e fluctuations on the downstream surface; At Mach 2.5, a weak shear layer i nstability produces a reduction in the sound pressure level, and the increa sed distance between the leading edge and the trailing edge produces a redu ction in frequency. An increase in the mean pressure drag coefficient is pr oduced due to the high pressure on the ramp. When an expansion surface is e mployed, the mean pressure drag coefficient is also increased slightly. Whe n the flow is attached to the surface, the major flow physics are similar t o the baseline case. A reduction of the sound pressure level is observed in the cavity with the surface height. When a shock induced separation occurs on the surface, a steady flow is established in the cavity. When the mass injection is introduced, a passive pressure response is observed at the lea ding edge, producing local vorticity and vortex shedding. The flow mechanis m remains the same at both Mach numbers, with a weak sitting vortex near th e rear corner. An optimal mass injection pressure ratio is identified. (C) 1999 Academic Press.