An Experimental Study of Low Speed Open Cavity Flows

The experimental work is part of an ongoing study aimed at understanding and controlling of cavity instabilities by passive or active steady or unsteady fluid injection. An experimental setup has been designed to quantitatively visualize the flow-field inside the cavity for varying relative dimensions (L/D ratios of 2.0, 2.67, 3.5 and 4.5, W/D of 3.33) at low subsonic speeds ranging from 55 ft/sec to 214 ft/sec using Particle Image Velocimetry (PIV).

The results showed that PIV could provide instantaneous velocity and other flow field data inside and above the cavity. The quality of data is good and may be used for validation of numerical predictions. Post-processing of the velocity data provided vorticity and other useful information in the measurement region. Velocity profiles along the shear layer showed shear layer growth towards downstream and a large re-circulation region inside the cavity. As L/D increased, the re-circulation zone was stronger and was located towards the rear of the cavity. Animations of the vorticity contour images clearly showed vortical disturbances in the shear layer that was convected downstream. It also showed the shear layer oscillating near the trailing edge indicating mass addition and removal process at the trailing edge. Unsteady pressure results showed the selected cavity configurations were oscillating in the selected speed range having peak sound pressure levels ranging from 115 to 133dB.