URANS simulation and experimental validation of axial flow-induced vibrations on a blunt-end cantilever rod for nuclear applications

Abstract

Fretting wear caused by flow-induced vibration is a leading cause of fuel failure in light water nuclear reactors. This study describes a numerical methodology, validated with dedicated experiments, for predicting flow-induced vibrations in cantilever rods exposed to axial water flow, a paradigmatic configuration informative for fuel rods in water-cooled nuclear reactor cores. Utilising strong two-way fluid-structure interaction (FSI) simulations with an efficient computational approach, the study focuses on two key aspects of self-excited FIV: the dominant vibration frequency and the amplitude of the vibration. The former depends on optimising the solid domain and FSI coupling, while the latter hinges on the fluid solver’s ability to accurately replicate unsteady flow behaviour, especially in areas of flow separation. Various URANS turbulence models and divergence numerical schemes were evaluated for their capacity to reproduce the correct unsteady flow behaviour. When the axial flow is directed from the free-end to the fixed-end of the rod, both the Eddy Viscosity Model (EVM) k-ω SST and the Reynolds Stress Model (RSM) by Launder, Reece, and Rodi (LRR) reliably predicted the frequency and amplitude of vibrations for a Reynolds number range between 16.4k and 61.7k. When the axial flow is directed from the fixed end to the free end of the rod, while vibrations frequencies were accurately modelled, replicating precise unsteady flow behaviour proved more challenging. The study underscores the importance of properly resolving the flow in areas of flow separation to achieve accurate unsteady flow behaviour.