Abstract
Turbulent scalar transport phenomena at high Prandtl numbers up to Pr=100 were examined through direct numerical simulations of forced isotropic turbulence with a constant mean temperature gradient. The main storage required for computation was significantly reduced by employing a different number of numerical grids for each of the velocity and temperature fields, which contained markedly different microscales. At high Prandtl numbers, the pressure temperature-gradient correlation was found dominant, instead of the molecular dissipation, as a sink term in the turbulent heat flux budget. It was also found that low-wave-number components of the velocity fluctuation were solely responsible for the cascade of the temperature fluctuation irrespective of the Prandtl number.
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