An examination of the scaling issue through the DNS of turbulent channel flow with or without heat transfer up to Re_τ=640

Direct numerical simulation (DNS) of turbulent heat transfer in a channel flow has been carried out with a higher Reynolds number up to Re_τ=640,which is based on the friction velocity u_τ and the channel half width δ. The configuration is a fully developed turbulent channel flow with uniform heating from both walls. Calculated conditions are Reynolds numbers of 180,395 and 640 and the molecular Prandtl numbers of 0.025 and 0.71. Turbulence quantities such as temperature variance, turbulent heat fluxes, their correlation coefficients, turbulent Prandtl number and time scale ratio are presented to investigate the Reynolds- and Prandtl-number effects and the scaling issue up to Re_τ=640.