Angular flow-induced vibrations of a triangular prism

We discuss flow-induced vibrations of an equilateral triangular prism confined to travel on a circular path when placed in the concave or convex orientations with respect to the flow. In each orientation, we consider three different initial angles for the prism. In Case 1, one side of the prism sees the flow first; in Case 2, one sharp edge sees the flow first; and in Case 3, one side of the prism is parallel to the incoming flow. We show that the response of the structure as well as the observed wake depend heavily on both the orientation and the initial angle of the prism. Case 1 exhibits vortex-induced vibration (VIV) in the concave orientation and galloping in the convex orientation. Case 2 does not oscillate in the concave orientation; however, oscillates about a mean deflection after a critical reduced velocity in the convex orientation. Case 3 exhibits small-amplitude oscillations in the concave orientation about a mean deflection, while in the convex orientation, exhibits VIV at low reduced velocities, followed by an asymmetric response with VIV features in a half-cycle and galloping features in the other half, and divergence at higher reduced velocities. These different types of responses are accompanied by a myriad of vortex patterns in the wake, from two single vortices shed in the wake in each cycle of oscillations to two vortex pairs, two sets of co-rotating vortices, and a combination of single vortices and vortex pairs depending on the prism’s orientation and its initial angle.