Numerical investigation of bifurcation characteristics under perturbations in vortex induced vibration of cylinder with two degrees of freedom

Abstract

In this paper, the bifurcation characteristics and perturbation response in vortex induced vibration of cylinder with two degrees of freedom is investigated, aiming to study the law and mechanism of the influence of perturbation on the bifurcation of vortex-induced vibration, and to give some engineering suggestions. The main content of this paper is to observe the variation of the amplitude, frequency, lift and drag coefficients of the vortex-induced vibration response of the cylinder after suddenly perturbing the cylinder displacement, to investigate the influence of displacement perturbations on bifurcation characteristics. Then through vorticity map analysis, the mechanism is further analyzed from the point of view of flow field. The results show that when the displacement perturbation is applied, the motion state of the cylinder will change, which will cause the change of the shedding mode and the wake mode of the vortex, resulting in the instability of the flow field. Then under the coupling action of disturbed flow field and cylinder motion, the flow field and the vibration state of the cylinder finally stabilize to the corresponding state of the upper branch or the lower branch, depending on the direction and magnitude of the perturbation. It can be concluded that in the velocity range near the branch jump points (upper and lower branches), the cylinder's vortex induced vibration may have two relatively stable states and can be transformed to each other under appropriate excitation of perturbations. Finally, some suggestions are given, based on the above results.