Vortex excitation of prisms with elongated rectangular, H and [vdash ] cross-sections

Abstract

This is an experimental investigation of vortex excitation of prisms with elongated rectangular, H- and [vdash ]-shaped cross-sections, where the depth parallel to the flow is much greater than the height perpendicular to the flow. Measurements are made of free oscillations in a wind tunnel and flow visualizations in a water tank. The flow around elongated bluff prisms is dominated by the impinging-shear- layer instability where the separated shear layers become unstable in the presence of different kinds of shape of the rear part of the cross-section, which may include sharp trailing edges. The two unstable shear layers interact with each other when they meet together downstream of the prism, thereby forming Kármán vortices with the same frequency of oscillation. The former impinging-shear-layer instability is largely responsible for vortex excitation of elongated bluff prisms.