Numerical Simulation and Validation of Flow-Induced Vibration of the Specific Rod under Elastic Supports using One-Way Fluid-Solid Interaction

Abstract

The vibration induced by the cooling fluid flow around the fuel rods in the fuel Assembly of nuclear reactors causes the rods to be destroyed and eventually leak due to the fretting wear in the place of contact with their supports for a long time. In this paper, the vibration caused by axial fluid flow around a specific fuel rod under elastic supports is numerically simulated. In this study, the fluid flow is modeled using the Large Eddy Simulation (LES) turbulence model in the FLUENT software. The fluid-structure interaction is also modeled using the ANSYS coupling system. To validate the implemented numerical model, the test results of the reported brass rod vibration similar to the studied problem in this research are used. Due to the long execution time of the two-way fluid-structure interaction simulations with a high grid number, the one-way fluid-structure interaction method is proposed. The results of simulations show that the one-way fluid-structure interaction method can be used in cases where the vibration amplitude of the structure is less than the height of the viscous sub-layer. Also, this method reduces the simulation time by 80%. Finally, the results of the flow-induced vibration simulation of the fuel rod show that the vibration range of the fuel rod will increase by 20 times if the contact of the elastic supports with the rod is lost, which will lead to the intensification of the wear caused by the rod oscillation. Also, the main natural frequency of the rod decreases when the rod loses contact with the supports and falls within the range of the reactor excitation frequency, i.e. 0 to 50 Hz, which should be avoided.