REYNOLDS AND PRANDTL NUMBER EFFECTS ON THE TURBULENT HEAT TRANSFER IN A CHANNEL FLOW THROUGH HIGH SPACIAL RESOLUTION DNS

摘要

Direct numerical simulation (DNS) of turbulent heat trans- fer in a fully developed channel flow for various Prandtl numbers Pr ranging from 0.71 to 10 has been carried out to investigate Reynolds-number dependences of the turbulence statistics and the instantaneous temperature field. The Reynolds number Re τ is set to be 180 and 395, where Re τ is based on the friction velocity and the channel half width. The turbulence statistics such as the mean temperature, the time scale ratio, the turbulent Prandtl number and the skewness and flatness factors are obtained through high spacial resolution and disscussed with focus on the effects of Reynolds number for high Pr. It is revealed that the profile of the mean temperature within the logarithmic region for Pr >1 decreases with increasing Re τ because the thermal field is mixed more thoroughly with increasing Re τ . Consequently, the R.M.S. of the temperature fluctuations is smaller at the channel center for Pr >1 at the higher Re τ . In addition, the low and high temperature streaky structures near the wall in the instantaneous fields are visualized. It is shown that their spacing in the spanwise direction is about 100 in viscous wall-unit and is mostly independent of Re τ for Pr =10.