Analysis of the modal characteristics of NHR200-II fuel rods in turbulent axial flow

The dynamics of vibrating fuel rods under axial fluid flows in a 200 MW nuclear heating reactor (NHR200-II) was analyzed through Fluid-Structure Interaction (FSI) simulations. Various inflow velocities and turbulence inlet conditions were considered to assess their influence on the system’s modal properties. The turbulent fluid flow was modelled by Unsteady Reynolds-Averaged Navier–Stokes (URANS) approach, while the rod was treated as an elastic solid. Numerical simulations were conducted utilizing the two-way coupling FSI solver in the commercial code LS-DYNA. The computational results indicate that the vibrating frequency remains largely insensitive to inflow velocities ranging from 0 to 6 m/s, whereas modal damping ratio increases with higher velocities. Turbulence inlet conditions were found to have a negligible effect on rod vibrations in specified inflow velocities. Furthermore, the added mass and damping for an inflow velocity of 1.0 m/s were evaluated as a demonstration and successfully integrated into the relevant structural solver.