CFD assessment of RANS turbulence modeling for solidification in internal flows against experiments and higher fidelity LBM-LES phase change model

Generation-IV nuclear reactors' potential coolant candidates include molten salts and liquid metals. Owing to their high melting temperature, both the design and safety assessments of these reactors need to take into consideration potential solidification events during normal or abnormal operation. This work assesses the Finite Volume Computational Fluid Dynamics (FV-CFD) enthalpy-porosity method combined with the Reynolds Averaged Navier Stokes (RANS) model k-! to model internal solidification under turbulent flow conditions for high and low Prandtl numbers at a moderate computational cost, which is required for full-core nuclear reactor analyses. Concerning high Prandtl numbers, the predictions of macroscopic quantities generated by the FVCFD RANS model are contrasted against a well-known internal solidification experiment on water (Thomason et al., 1978). A key factor in the satisfactory agreement between the CFD RANS model and the experiment is the addition of an interface turbulence-damping source to the specific dissipation rate equation (!). For the low Prandtl numbers involved in liquid metals, there is a lack of high-fidelity experiments due to the complicated measurements. Thus, to perform the FV-CFD RANS model assessment, we develop and validate a high-fidelity phase-change model based on the Lattice Boltzmann Method (LBM) with a Large Eddy Simulation (LES) turbulence model. To the author's knowledge, this is the first attempt to integrate LES turbulence models with phase-change solidification in the LBM context. Considering the computational time advantage of the FVCFD RANS model over higher fidelity models and the good agreement of its predictions against experiments and the LES model demonstrated, this work demonstrates that FV-CFD RANS is an attractive tool to model internal turbulent solidification.