Turbulent Schmidt numbers for CFD analysis with various types of flowfield

The application of CFD (computational fluid dynamics) using RANS (Reynolds-averaged Navier–Stokes equations) model to turbulent flows with mass transfer generally estimates the turbulent scalar flux assuming the gradient diffusion hypothesis, which requires definition of the turbulent Schmidt number, Sct However, no universal value of Sct has been established and empirical values have been used in different studies. In this paper, previous research related to the application of optimum values of Sct for engineering flowfields relevant to atmospheric dispersion is reviewed. The optimum values for Sct are widely distributed in the range of 0.2–1.3 and the specific value selected has a significant effect on the prediction results. On the basis of the present study results and since the optimum values of Sct largely depend on the local flow characteristics, it is recommended that Sct should be determined by considering the dominant flow structure in each case.