Direct numerical simulation of turbulent heat transport at high Prandtl numbers

Turbulent scalar transport phenomena at high Prandtl numbers up to Pr=100 w ere examined through direct numerical simulations of forced isotropic turbu lence with a constant mean temperature gradient. The main storage required for computation was significantly reduced by employing a different number o f numerical grids for each of the velocity and temperature fields, which co ntained markedly different microscales. At high Prandtl numbers, the pressu re temperature-gradient correlation was found dominant, instead of the mole cular dissipation, as a sink term in the turbulent heat flux budget. It was also found that low-wave-number components of the velocity fluctuation wer e solely responsible for the cascade of the temperature fluctuation irrespe ctive of the Prandtl number.