Numerical Study of Flow-Induced Vibration of Fuel Rods

In this work, Fluid-Structure Interaction (FSI) simulations are performed to study Flow Induced Vibrations (FIV) of nuclear fuel rods using the commercial code STAR-CCM+. The Navier-Stokes equations are solved on deforming grids with the Arbitrary Eulerian-Lagrangian (ALE) formulation. The finite element method is used to solve the linear elastic problem for the structure. The two solvers are tightly coupled together with the Gauss-Seidel method to solve the FSI problem. The first part of the work focuses on the FIV of a single rod. Two types of rods are considered: 1) a bare rod and 2) a rod with a wire spacer helically wrapped around its external surface. For the case of the bare rod configuration, the effects of the working fluid on the dynamics is investigated and a correlation for the frequencies as function of density is proposed. The second part of the work focuses on the analysis of FIV for two different configurations of bare seven-rod bundle. One of the main features of the considered configurations is the appearance of axial flow fluctuations in the rod gaps due to the velocity difference in the sub-channels between the rods. Therefore, this part of the work focuses on the study of the effect of the velocity pulsations on the vibrations of the rods.