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, Sc_t However, no universal value of Sc_t 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 Sc_t for engineering flowfields relevant to atmospheric dispersion is reviewed. The optimum values for Sc_t 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 Sc_t largely depend on the local flow characteristics, it is recommended that Sc_t should be determined by considering the dominant flow structure in each case.