EFFECTS OF SCHMIDT NUMBER ON TURBULENT MASS TRANSFER IN PIPE FLOW

초록

Large Eddy Simulation (LES) of turbulent mass transfer in circular-pipe flow has been performed to investigate the effects of Schmidt number on the turbulent mass transfer. We consider a fully developed turbulent pipe flow with a constant wall concentration. The Reynolds number under consideration is Reτ=500 based on the friction velocity and the pipe radius, and the Schmidt numbers are 0.71, 5, 10, 20 and 100. Dynamic subgrid-scale (SGS) models for the turbulent SGS stresses and mass fluxes are employed to close the governing equations. In this investigation, we examine the reliability of the LES technique for predicting turbulent mass transfer at high-Schmidt numbers and analyze the behavior of turbulent mass diffusion from the wall at different Schmidt numbers. To show the effects of Schmidt number on the turbulent mass transfer, the statistical quantities such as the mean concentration profile, concentration variance, turbulent mass fluxes, turbulent Schmidt number, and mass transfer coefficients are presented. Turbulence budgets for concentration variance and turbulent mass fluxes are computed and the effect of Schmidt number is identified. In addition, to understand the correlation between near-wall turbulence structure and concentration fluctuation, we carry out an Octant analysis in the vicinity of the pipe wall.