Numerical study on vortex-induced vibration mechanism of a rectangular 5:1 cylinder at different vibration stages

In this research, the vortex-induced vibration (VIV) mechanism is investigated from the viewpoints of vibration response, aerodynamic characteristics, and vortex shifting based on a three-dimensional large eddy simulation of a 5:1 rectangular cylinder at different vibration stages. An explanation of the self-limiting amplitude characteristics of the prolate cylinder under VIV is given with emphasis on the flow field point of view. With the increase in the reduced velocity, the phase shift of the vortex core relative to the vibration velocity gradually increases, resulting in the increase in the aerodynamic force phase angle relative to the vibration velocity, which is the main reason for the deviation of the maximum amplitude velocity from the resonance velocity. In addition, the position of the vortex core center gradually moves to the trailing edge with the increase in the reduced velocity, which results in a more significant contribution of the distributed aerodynamic force near the trailing edge to the vibration amplitude. From the standpoint of flow field evolution based on dynamic mode decomposition, the vibration-frequency and Strouhal-frequency modes are in a competitive relationship, and the energy changes between the two modes and the vorticity strength in the flow field influence the VIV development stage of the rectangular cylinder.