Discussion of High-Prandtl Number Effect on Inner Layer Turbulent Heat Flux in High-Reynolds Number Channel Flows

Abstract

Prandtl number (Pr) effects on characteristics of the thermal boundary layer were investigated by means of Direct Numerical Simulations (DNS) in high-Reynolds number turbulent channel flows. The molecular Pr conditions were changed from 0.71 to 25.0, and the Reynolds number based on the friction velocity and channel half-width was kept to 1000 in all cases. In the thermal conduction sub-layer and logarithmic layer, despite difference of Pr, Joint probability density function (JPDF) profiles of the wall-normal turbulent heat flux were shown good agreements with JPDF profiles of the Reynolds shear stress. On the other hand, in the peak wall-normal height of streamwise velocity intensities, JPDF profiles of wall-normal turbulent heat flux were influenced on Pr. In fact, the temperature fluctuations increase with increase of Pr at this wall-normal position. This is caused from high-Pr effects such as the difference between velocityand thermal boundary thicknesses and low-thermal conductivity.