Research on Cross Flow Induced Vibration of Flexible Tube Bundle

When the elastic deformation of the tube bundle is considered, the interaction between the flow field and the structure becomes more complicated. In order to investigate the flow induced vibration (FIV) problems in flexible tube bundle, a numerical model for fluid-structure interaction system was presented firstly. The unsteady three-dimensional Navier-Stokes equation and LES turbulence model were solved with the finite volume approach on structured grids combined with the technique of dynamic mesh. The dynamic equilibrium equation was discretized according to the finite element theory. The configurations considered are tubes in a cross flow. Firstly, the flow-induced vibration of a single flexible tube under uniform turbulent flow are calculated when Reynolds number is 1.35× 10⁴. The variety trends of lift, drag, displacement, vertex shedding frequency, phase difference of tube are analyzed under different frequency ratios. The nonlinear phenomena of locked-in, phase-switch are captured successfully. Meanwhile, the limit cycle and bifurcation of lift coefficient and displacement are analyzed using trajectory, phase portrait and Poincare sections. Secondly, the mutual interaction of two in-line flexible tubes is investigated. Different behaviors, bounded by critical distances between the tubes, critical velocity, and wake vortex pattern are highlighted. Finally, four tube bundle models were established to study the effect of the number of flexible tube on the FIV characteristics. Thanks to several calculations, the critical velocity of instability vibration and the effect of tube bundle configurations on fluid forces and dynamics were obtained successfully. It is therefore expected that further calculations, with model refinements and other validation studies, will bring valuable informations about bundle stability. Further comparisons with experiment are necessary to validate the behavior of the method in this configuration.