Shock and shear layer interaction in a confined supersonic cavity flow

Abstract

The impinging shock of varying strengths on the free shear layer in a confined supersonic cavity flow is studied numerically using the detached-eddy simulation. The resulting spatiotemporal variations are analyzed between the different cases using unsteady statistics, x − t diagrams, spectral analysis, and modal decomposition. A confined passage height of H/D = 2 and a cavity of length to depth ratio L/D = 2 at a freestream Mach number of M ∞ = 1.71 is considered. Impinging shock strength is controlled by changing the ramp angle (θ ) on the top-wall. The static pressure change across the impinging shock (p 2 /p 1 ) is used to quantify the shock strength. Five different cases are realized: [p 2 /p 1 ] = 1.0, 1.2, 1.5, 1.7 and 2.0. At [p 2 /p 1 ] = 1.5, fundamental fluidic mode or Rossiter's frequency corresponding to n = 1 mode vanishes whereas frequencies correspond to higher modes (n = 2 and 4) resonate. Wavefronts interaction from the longitudinal reflections inside the cavity with the transverse disturbances from the shock-shear layer interactions is identified to drive the strong resonant behavior. Due to Mach-reflections inside the confined passage at [p 2 /p 1 ] = 2.0, shock-cavity resonance is lost. Besides, the cavity wall experiences a higher pressure of 25% for [p 2 /p 1 ] = 1.0 due to shock loading. Based on the present findings, an idea to use a shock-laden confined cavity flow in an enclosed supersonic wall-jet configuration as passive flow control or a fluidic device is also demonstrated.