Flow and Heat Transfer Simulation in a Complete PWR Fuel Assembly Using Wall-Modelled Rans

Reproduction of turbulent flow and heat transfer inside a pressurized water reactor (PWR) fuel assembly is a challenging task due to the complex geometry and the huge computational domain. Capability of a wall-modeled Reynolds-averaged Navier–Stokes (RANS) simulation approach has been examined, which had already been validated against the measurements of the MATiS-H experiment. The method is here expanded to a larger computational domain aiming to reproduce flow and thermal field in the entire PWR fuel assembly. Namely, in the first part of this study, wall-modeled RANS is performed in a relatively short section of the representative PWR fuel assembly containing one single mixing grid with an array of 15 × 15 fuel rods. Linear and nonlinear eddy-viscosity turbulence models have been applied; however no significant difference is observed in the predicted pressure drop in the fuel assembly. The obtained predictions revealed an interesting pattern of swirl flow as well as diagonal cross flow downstream the mixing grid, which is driven by the applied design of split-type mixing vanes. In the second part, the computational model is extended to a domain representative of a complete PWR fuel assembly with ten mixing grids, inlet and outlet sections. Pressure drop and flow field are analyzed together with the predicted temperature and potential hot spots. In spite of a relatively coarse spatial resolution of the applied approach, the wall-modeled RANS provided promising results at least for the qualitative prediction of the pressure, flow field, and location of hot spots.