Vortex-Induced Vibration Characteristics for a Three Dimensional Flexible Tube

In order to study the vortex-induced vibration, the three-dimensional unsteady, viscous, incompressible Navier-Stokes equation and LES turbulence model are solved with the finite volume approach, and the dynamic equilibrium equations are discretized by the finite element theory. A three-dimensional numerical model for flexible tube vibration induced by cross flow is proposed. The model realized the fluid-structure interaction with solving the fluid flow and the structure vibration simultaneously. Based on this model, the dynamic behavior and response characteristic of the tube are investigated. Meanwhile, the limit cycle and bifurcation of lift coefficient and displacement are analyzed. Amplitude response, trajectory, phase difference, fluid force coefficient and vortex shedding frequency are obtained. The results reveal that, a quasi-upper branch is found in the present fluid-flexible tube coupling system with high mass-damping and low mass ratio. The three-dimensional flexible tube has a broader synchronization range and the amplitude is higher than elastically mounted two-dimensional rigid tube. In the quasi-upper branch and lower branch regime, the “lock-in” begins. In quasi-upper branch, the lateral amplitude increases with reduced velocity increasing. While in lower branch, the amplitude keeps almost constant. The drag force reaches its peak value before lift. The lift coefficient reaches its maximum value at the switch from initial branch to quasi-upper branch. The phase angle reaches zero under “lock-in” and the dynamic behavior is a periodic motion. There is no bifurcation of lift coefficient and lateral displacement occurred in three dimensional flexible tube submitted to uniform turbulent flow.