8.9.5 Mass Diffusion Coefficient Inputs for Turbulent Flow

When your flow is turbulent, you will define $D_{i,m}$ or ${\cal D}_{ij}$, as described for laminar flows in Section  8.9.4, and you will also have the option to alter the default setting for the turbulent Schmidt number, ${\rm Sc}_t$, as defined in Equation  8.9-4.

Usually, in a turbulent flow, the mass diffusion is dominated by the turbulent transport as determined by the turbulent Schmidt number (Equation  8.9-4). The turbulent Schmidt number measures the relative diffusion of momentum and mass due to turbulence and is on the order of unity in all turbulent flows. Because the turbulent Schmidt number is an empirical constant that is relatively insensitive to the molecular fluid properties, you will have little reason to alter the default value (0.7) for any species.

Should you wish to modify the Schmidt number, enter a new value for Turb. Schmidt Number in the Viscous Model dialog box.

Models Viscous Edit...

Note that the full multicomponent diffusion model described in Section  8.9.2 is not recommended for turbulent flows.