Experimental Study of Shear-Layer/Acoustics Coupling in Mach 5 Cavity Flow

Abstract

Simultaneous planar laser imaging and e uctuating-pressure measurements were made in a high-Reynolds- number, Mach 5 cavity e ow, with cavity length-to-depth ratios of 3, 4, 5, 6, and 7. Instantaneous planar laser scattering images show no evidence for coherent structures that are induced by the cavity acoustics. Furthermore, both the pressure measurements and imaging suggest that the rear-wall shock is caused by the impingement of shear-layer turbulent structures. Analysis of the e uctuating-pressure data suggests that the shock frequencies and the duration of the impingement shock are not sensitive to cavity length-to-depth ratio. Ensemble-average velocity proe les in the shear layer, conditioned on the front-wall pressure, suggest that the dee ection of the shear layer is not measurably correlated with the cavity oscillation cycle. In addition, spectral analysis of the e uctuating pressures shows that the cavity oscillation frequencies are accurately predicted using simple closed-box acoustic theory. These results suggest that the present cavity e ow exhibits substantially less coupling between the cavity pressure e uctuations and the shear-layer e uid dynamics as compared to similar e ows at lower Mach numbers.