Fluid-structure interaction analysis of a 4:1 rectangular prism undergoing vortex-induced vibration

The vortex-induced vibration (VIV) characteristics and fluid-structure interaction mechanism of a 4:1 rectangular prism is investigated in this study based on large-eddy simulations. Variations of the vibration amplitude, vortex-induced force, and surface pressure with the inflow velocity (U∗) are analyzed. Some significant questions regarding the VIV responses are raised and explained based on dynamic mode decomposition (DMD) and phase analyses of the flow fields. The cooperative shedding process of the motion-induced leading-edge vortex and the Karmon-type trailing-edge vortex that sustains the VIV is identified in the DMD mode. It is found that the phase difference between the leading and trailing-edge vortices in the near wake increases with U∗, leading to the eventual disappearance of VIV at a critical U∗. The root-mean-squared lift coefficient (C_L_rms) reaches its highest value in the initial phase of lock-in range, and then shows a monotonic reduction with increasing U∗. However, the structure could maintain a relatively large vibration amplitude until VIV disappears, even though the C_L_rms may be as low as that for the static case. This phenomenon is explained in detail based on the variations in phase distributions of the surface pressure with increasing U∗.