Analysis of flow induced vibrations and static deformations of fuel rods considering the effects of wire spacers and working fluids

In this study, fluid–structure interaction (FSI) simulations of a single cylindrical rod in axial turbulent flows of water and liquid metal are performed. Two types of rods are considered: (1) a bare rod and (2) a rod with a wire spacer helically wrapped around its external surface. The effects of the working fluid and of the rod type are analyzed for the configuration selected in this work. Considering the effect of the wire spacer, it is found that the dynamics of the displacement of the wire-wrapped rod is very different from that of the bare rod due to the asymmetry in the flow field introduced by the wire spacer. Moreover, the wire spacer has a small effect on the value of the natural frequencies, while larger effects are observed on the value of the damping ratio with the liquid metal fluid. The effect of the wire spacer is then investigated in more detail. To this purpose, dynamic simulations of rod configurations with different values of pitch length are performed. It is found that for an integer rod-to-wire-pitch-length-ratio higher damping ratios are observed, whereas the frequencies are less sensitive to the pitch length. As next step, static FSI analyses are performed to study the effect of different wire spacer configurations on the static deformation of the rods. It is found that the distribution of the forces on the rod follows closely the geometry of the wire spacer wrapped around the rod due to the modification of the flow field produced by the presence of the wire. By means of static simulations, the effect of the rod constraints, working fluids and mesh resolutions are also investigated. Finally, the effect of using different numbers of wire pitches with the same pitch length is investigated.