Large eddy simulation of passive scalar transport in a stirred tank for different diffusivities

Large eddy simulation of flow and passive scalar transport in a stirred tank has been carried out for three different Reynolds numbers of 4000, 16,000 and 64,000 and corresponding molecular diffusivities of 1.6 x 10(-4), 4.3 x 10(-5) and 1.1 x 10(-5), respectively, using a spectral multi-domain method. The time sequence of concentration and flow fields are explored to investigate the dependency of the concentration development on the flow structure. The sharp gradients of the instantaneous and mean concentrations are distributed around the center of larger ring vortices at high molecular diffusivity. With decreasing molecular diffusivity and increasing Reynolds number, the distribution of concentration becomes much uniform. The eddy diffusivity and subgrid scale dissipation are widely spread from the impeller jet toward outer wall and also the regions possessing small dissipation becomes diminished with increasing Reynolds number and decreasing the molecular diffusivity. (C) 2015 Elsevier Ltd. All rights reserved.