Large-eddy simulation of heat-generating molten salt flows in wall-bounded geometries: Application to molten salt reactors

Turbulent wall-bounded molten salt flows are encountered in Molten Salt Reactors (MSRs), where heat is generated volumetrically within the fluid due to nuclear reactions. This work aims to quantify the influence of volumetric heat generation on both Kolmogorov scales and large scales across different layers of turbulent molten salt flows characterized by low kinematic viscosity and high Prandtl numbers. For this purpose, turbulent channel flow of molten salt with variable thermophysical properties is modeled using Large-Eddy Simulation (LES). To verify the LES framework, a grid resolution study is first performed and the performance of five subgrid-scale (SGS) models (Smagorinsky, Turbulent Kinetic Energy (TKE), buoyancy-modified TKE, dynamic TKE, and WALE), together with an SGS-free approach are assessed through comparison with DNS data. The results demonstrate that the presence of a volumetric heat generation enhances SGS kinetic energy in the buffer layer (y+ < 40) while decreasing it in the outer layer. As a result, the Reynolds stress components increase in the near-wall region while decreasing at the channel center. Moreover, the mean Kolmogorov velocity scale ((Formula presented) ) decreases, while the mean Kolmogorov length scale ((Formula presented) ) increases. Additionally, the results indicate that constant coefficient models, such as Smagorinsky and TKE fail to predict the solution accurately. Compared with the reference correlations, these models underpredict the friction factor by 39% and the Nusselt number by 82%, owing to their high dissipation rates and consequent inability to resolve small eddies. However, incorporating the buoyancy term into the TKE equation improves velocity predictions in the outer layers ((Formula presented) ).