Direct numerical simulation of turbulent particle-laden flows: effects of Prandtl and Stokes numbers

Abstract

The effect of molecular Prandtl number on the turbulent heat transfer of a non-isothermal turbulent channel flow laden with particles with four different Stokes number is investigated using direct numerical simulation coupled with a Lagrangian particle tracking. The flow configuration is a downward vertical channel with side walls kept at constant temperature. A total of 16 test cases with four different Prandtl numbers of Pr = 0.71, 1, 3, 7, and four particle sizes with the Stokes numbers of St= 40, 60, 100, 190 are considered. The mass loading, particle-to-fluid density ratio, and specific heat ratio are constant for all cases and they are equal to 0.57, 7298, and 0.39, respectively. It is shown that by the addition of particles, the heat transfer rate decreases and the thickness of the conductive sublayer thickness increases for all cases. The percentage of heat transfer modulation resulting from the addition of particles is almost independent of the Prandtl number but it slightly depends on the size of the particles, with the maximum being for smaller particles. The mean and rms values of temperature, temperature-velocity correlations, mean energy equation, and temperature variance budgets are presented. Contours of temperature in planes parallel to the wall and normal to the streamwise direction are also reported. At higher Prandtl numbers, the temperature contours clearly visualize the mushroom shaped structures formed as a result of the ejection of low-speed fluid from the wall.