RANS simulation of turbulent swept flow over a wire in a channel for core thermal hydraulic design using K-Epsilon turbulence models

This paper presents a thermal hydraulic investigation of a nuclear reactor core, which is one of the most important components in the design of a nuclear power plant. Helical wire-wrapped fuel assemblies have been suggested for coolant mixing, and from a design point of view, an understanding of the influence of the reattachment length and recirculation bubbles could aid in determining the structural parameters for an optimal core thermal hydraulic design. In this study, assessments of Reynolds Averaged Navier-Stokes (RANS) based turbulence models were performed under various flow conditions for a wire in a channel. The calculation results were compared with the DNS results in terms of mean flow analysis and turbulent kinetic energy for further thermal hydraulic design of a wire-wrapped fuel assembly reactor core. The k- epsilon models with a two-layer wall treatment were chosen to predict the turbulent statistics of flow for four cases of a Reynolds equivalent flow rate of 0 to 1,709 along the cross-flow direction and an identical axial flow rate of 5,400. The selected standard k-epsilon models with three different constitutive relationships and a realizable k-epsilon model with the two-layer approach as the turbulence model revealed the locations of flow characteristics of interest, especially recirculation and reattachment, and showed that axial and cross-flow directional velocity profiles are fairly well matched. Relative to the DNS results, the errors in terms of reattachment lengths are approximately 1% for proper turbulence models in each case. From the well-matched flow modeling results and economical computing resources of the k-epsilon model, we conclude that this approach offers sufficient capability as an engineering design tool for core thermal hydraulics.