Experimental study of shear-layer/acoustics coupling in Mach 5 cavity flow

Simultaneous planar laser imaging and fluctuating-pressure measurements wer e made in a high-Reynolds-number, Mach 5 cavity how with cavity length-to-d epth ratios of 3, 4, 5, 6, and 7. Instantaneous planar laser scattering ima ges 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 turbu lent structures. Analysis of the fluctuating-pressure data suggests that th e shock frequencies and the duration of the impingement shock are not sensi tive to cavity length-to-depth ratio. Ensemble-average velocity profiles in the shear layer conditioned on the front-wall pressure, suggest that the d eflection of the shear layer is not measurably correlated with the cavity o scillation cycle. In addition, spectral analysis of the fluctuating pressur es shows that the cavity oscillation frequencies are accurately predicted u sing simple closed-box acoustic theory. These results suggest that the pres ent cavity flow exhibits substantially less coupling between the cavity pre ssure fluctuations and the shear-layer fluid dynamics as compared to simila r hows at lower Mach numbers.