Direct Numerical Simulation of Turbulent Mass Transfer around a Rotating Circular Cylinder

초록

Characteristics of turbulent mass transfer around a rotating circular cylinder are investigated by Direct Numerical Simulation for Schmidt numbers Sc=1 and 1670. The concentration field is computed for three different cases of low Reynolds number, Re=161, 348 and 623, based on the cylinder radius and friction velocity for Sc=1670. Results confirm that the thickness of Nernst diffusion layer is very small compared with that of viscous sub-layer in the case of high Sc mass transfer. Visualization of instantaneous concentration reveals that the length scale of concentration fluctuation typically decreases as Reynolds number increases. Reynolds analogy identified at Sc=1 causes a strong correlation between concentration fluctuation and streamwise velocity fluctuation. For Sc=1670, positive small values of concentration fluctuations are observed more often than for Sc=1 particularly outside of the range of Nernst diffusion layer but inside of the viscous sublayer. This fact is fully confirmed by detailed statistical study using a probability density function of concentration fluctuations.