Mechanism analysis of the effect of wake vortex on cylinder vibration in flow induced motion

Unsteady Reynolds averaged Navier-Stokes (RANS) method combined with Spalart-Allmaras turbulence model and dynamic mesh technology were used to investigate the impact of wake vortex on the vibration response of a cylinder. By analyzing the phase difference between the wake vortex force and the displacement under different mass parameters in flow-induced vibration (FIV), the study reveals that the influence of wake vortex on the cylinder varies significantly in different vibration branches. The wake vortex of the initial branch enhances the cylinder's vibration, whereas the wake vortices of the upper, lower, and desynchronized branches suppress the vibration. At the critical point between the initial branch and the upper branch of vortex induced vibration (VIV), there is a 90° phase jump, and the instantaneous phase difference fluctuation between the wake vortex force and displacement of the VIV branch remains relatively constant. In the galloping branch, there are wake vortices in different directions that affect the cylinder's vibration every quarter of the vibration period, and the phase difference undergoes periodic large fluctuations (either in-phase or out-of-phase), with the result that the wake vortex force periodically promotes or restrain the cylinder's vibration, which can serve as a novel criterion for identifying the occurrence of galloping. Furthermore, when varying the mass parameters at a constant reduced velocity, the impact of the wake vortex in the initial branch is relatively insignificant. However, as the mass ratio increases in other vibration branches, the suppressive effect increases, and the wake vortex force can prevent VIV induced galloping phenomenon by affecting the vibration intensity.