Vortex-induced vibrations of an elastically mounted disk: The characteristics of wake and trajectory

Vortex-induced vibration (VIV) of an elastically supported disk is investigated computationally using large-eddy-simulation (LES). The disk motion is constrained to move in the transverse plane vertical to the free stream. Two sets of simulations are conducted at Re=165 and 210 over the reduced velocity range 3≤U_R≤7.5 respectively. The disk shows a highly periodic large-amplitude vortex-induced vibration response over a certain reduced velocity range at both Reynolds numbers. The shedding of intertwined longitudinal spiral vortex in the wake of a vibrating disk is investigated for the first time in this paper. Moreover, we find a new wake mode named unsteady spiral (US) mode in the present work for a vibrating disk, except for reflectional-symmetry-breaking (RSB) mode and standing wave (SW) mode for a stationary disk. Our researches show the wake mode is not only related to the Reynolds number, but also to the vibration of the disk. When the wake is in the RSB mode, the disk moves along a linear path in the transverse plane, while the disk vibrates along a linear path under the SW mode, and the disk path is a perfect circle under the US mode. The transformation process from quasi-8-shaped trajectory to linear trajectory and from linear trajectory to circular trajectory are also presented and investigated.