Analysis of Vortex-Induced Vibration Characteristics for a Three Dimensional Flexible Tube

Numerical simulations of vortex-induced vibration of a three-dimensional flexible tube under uniform turbulent flow were calculated when Reynolds number was 1.35×10⁴. In order to achieve the vortex-induced vibration, the three-dimensional unsteady, viscous, incompressible Navier-Stokes equation and LES turbulence model were solved in the finite volume approach, the tube was discretized according to the finite element theory, and its dynamic equilibrium equations were solved by the Newmark method. The fluid-tube interaction was realized by the diffusion-based smooth dynamic mesh method. For a VIV system, the varying trends of lift coefficient, drag coefficient, displacement, vortex shedding frequency, phase difference angle of the tube were analyzed at different frequency ratios. The nonlinear phenomena of lock-in and phase-switch were captured successfully. Meanwhile, the limit cycle and bifurcation of the lift coefficient and displacement were analyzed with trajectory, phase portrait and Poincaré section mapping. The results reveal that: when the drag coefficient reaches its minimum value, the transverse vibration amplitude reaches its maximum and lock-in begins simultaneously. In the range of lock-in, the vibration amplitude decreases gradually with increase of the frequency ratio. When the lift coefficient reaches its minimum value, the phase difference between the lift coefficient and lateral displacement undergoes a sudden change from an out-of-phase to an in-phase mode. There is no bifurcation of the lift coefficient and lateral displacement occurring to the three dimensional flexible tube under uniform turbulent flow.