Turbulence budgets and statistics analysis of mixed convection liquid metal flow in horizontal channel using DNS

Mixed convection turbulent flows of liquid metal flowing through horizontal channel with varying Richardson number is studied using DNS. Fluids with Re-b = 4667 and Pr = 0.025 are simulated under four different Richardson number (Ri = 0, 0.25, 0.50, 1.00). The turbulence budgets and statistics analysis of mixing efficiency, time constant ratio and parametrization of heat transfer are extensively analyzed and discussed. We found that the diffusion of turbulent kinetic energy is quickly dissipated in the viscous sublayer. The rise of thermal plumes produces more (theta'+theta') over bar+/2 in the buffer layer and enhanced turbulent heat transfer. The valley value of production of (u'+theta') over bar moves closer to the hot wall with increasing Ri due to the more frequent generation of thermal plumes. The budgets of (u'+theta') over bar is almost independent of Ri. The mixing efficiency has sharp increase in the bulk region and it increases with the increase of buoyancy strength. The time constant ratio increases along the wall-normal direction of the channel and it is close to Pr in the viscous sublayer. An improved correlation of Nu, Ra and Re is formulated for low-Ra flow. By analyzing the DNS data, the turbulent heat transfer of liquid metals can be better understood. The DNS data is also compared with results from RANS models. The data provided in this paper have important practical value for developing and validating RANS models for liquid metal flow simulation, which can be useful for developing lead-cooled fast reactors and sodium-cooled fast reactors.