Direct Numerical Simulation of Turbulent Heat Transport at High Prandtl Numbers.

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