Mass ratio effects on flow-induced vibrations of an equilateral triangular prism

Abstract

In this paper, we numerically studied the effects of mass ratio (m∗) on three identified responses of a transversely oscillating equilateral triangular prism in Chen et al. (J. Fluids Struct., vol. 97, 2020, 103099). Three angles of attack, i.e. α=10°, 40° and 60°, were selected, with α=0° being the configuration that one vertex faces upstream. Our results indicated that m∗ exerts significant influences on both responses and wakes. At α=10°, a higher m∗ leads to a significant shrink of the large-amplitude vibration region while the largest amplitude occurs at a higher reduced velocity. At α=40°, increasing m∗ leads to the appearance of three distinct responses successively. At α=60°, soft galloping dominates at m∗=2–10, while hard galloping where an initial disturbance is required occurs at m∗=20. For the wake, only the 2S mode is observed at α=10° owing to the small amplitude, while depending on the response, P+S, 2S, competition, and mS+nS (miS+niS) modes can dominate at α=40°. At α=60°, 2S and mS+nS (miS+niS) modes occur. Furthermore, dynamic mode decomposition is applied to extract the vortex structures of different frequencies. Results indicate that von Karman and galloping modes coexist in the region where the galloping phenomenon appears. With increasing amplitude, the scale of the galloping mode increases, while the von Karman mode is almost unaffected. Flow physics for identified responses disclose that both vortex-induced vibration and galloping are closely related to the vortex formation process. The sustenance of the large amplitude in galloping is associated with the continuous shear layer reattachments since multiple vortices are shed from the prism.