Flow Around Axisymmetric and Two-dimensional Forward-Facing Cavities

Abstract

Flowfield of axisymmetric and two-dimensional forward facing cavities was investigated. Flow visualization results obtained using PLIF and hydrogen bubbles were used to develop a generic flow topology consisting of a combination of vortical structures, foci and a detached primary singular point. Ejection of large eddies from the cavity was closely related to the entrainment and exchange with the outer fluid flow for both types of cavities. Aspect ratio of the cavity had a strong effect on the flow inside the cavity. The primary singular point moved further downstream toward the interior of the cavity with increasing aspect ratio, and was off the geometric centerline due to unsteadiness of the cavity flow structures.

The Reynolds number however had a more pronounced effect on the vorticity and trajectory of the flow structures. Spectral analysis revealed that the shedding of the wake imposed subharmonics disturbances on the upstream flow resulted in the ejection of fluid structures from the cavity. The Strouhal number of the wake of the axisymmetric cavities increased with aspect ratio. The wake of the two-dimensional cavity closely followed classical two-dimensional bluff body wakes with a mean Strouhal number of 0.21.