Investigation on cross flow induced tube bundle vibration and tube-support contact state

Wear due to non-uniform cross flow induced vibration (FIV) challenging the integrity of tubes and fuel rods in nuclear reactors depends on the vibration trajectory and the contact state between the tube and the tube support plate. To reveal the characteristics of vibration and contact state of tubes suffering non-uniform cross flow, experimental investigation on the vibration response of a three-span 7x11 tube bundle subjected to cross-flow from a one-third opening baffle and a baffle with uniform holes has been carried out. Visualization measurement techniques have been developed to obtain the vibration trajectory of the tube in the middle of the first row and the micro-meter sale gap between the tube and the support plate at the top end. Numerical simulations were also conducted to analyze the flow field characteristics within the tube bundle formed by the one-third opening inlet flow. The results indicate that the tube bundle subjected to flow from a one-third open inlet is more prone to fluid-elastic instability compared to that with a uniformly perforated inlet. However, in the high velocity ranging from 1.52 m/s to 2.77 m/s before FEI, the case with uniform-hole baffle has higher vibration transverse displacement at the top end than the corresponding case with one-third opening baffle. The gap between the tube C1 (middle tube in the first row) and 2#TSP, and the top end trajectory of tube C1 is systematically analyzed. The contact states between this tube and the 2#TSP indicate that the tube stably leaning on the TSP is prone to adhesive wear before FEI for non-uniform flow case, while the tube experiencing serious displacement at contact location is prone to sliding wear before the FEI for uniform flow.