DNS of turbulent heat transfer under a uniform magnetic field at high Reynolds number

A low Pr number fluid flow, such as liquid-metals, has relatively less than turbulent heat transport capability because of the liquid-metals’ high thermal conductivity and its very large thermal boundary layer. Liquid-metals as coolant material in fusion reactor have a significant role in the design of advanced reactors. This is true since the investigation of thermal behavior in the actual facility environment such as in the case of low Pr number fluid flow, is needed at high Reynolds number under a magnetic field. In the present study, a direct numerical simulation (DNS) for the low Pr number fluid flow of turbulent heat transfer with high Reynolds number has been carried out to show the effects of magnetic field. The Reynolds number for channel flow based on bulk velocity Ub, viscosity ν, and channel width 2δ was set to be constant as Reb = 2δUb/ν = 45,818. A uniform magnetic field was applied in a direction perpendicular to the wall of the channel. The values of Hartmann number Ha   were 0 and 65 (where Ha=2δB0σ/ρν), and Prandtl number was 0.06. The turbulent quantities such as the mean temperature, turbulent heat flux, and temperature variant were obtained by DNS. Although large-scale turbulent structures of both velocity and temperature fields are found at the central region of the channel, the mean temperature profiles near wall region show up as laminar profile, that is, the thermal efficiency of the transport is less than that of turbulent flow. This means that it is necessary to consider the fusion reactor design of thermal mixing argumentation for low Pr number fluid flow because the heat transfer enhancement at turbulent flow cannot be acceptable even where the flow state happens to be a turbulent flow at high Reynolds number.