Turbulence Modeling in Mixture Models
Turbulence modeling is particularly relevant for dilute flows, that is, for flows with a low dispersed phase volume fraction. For dense flows, the mixture viscosity usually becomes high. In such cases, the flow is laminar and no turbulence modeling is necessary.
The Mixture Model, Turbulent Flow interfaces include the turbulence models described in Theory for the Turbulent Flow Interfaces.
The turbulence must be accounted for in the calculation of the dispersed phase volume fraction. This is accomplished by introducing a turbulent dispersion coefficient Dmd (SI unit: m2/s) in Equation 6-47 as
where σT is the turbulent particle Schmidt number (dimensionless). The particle Schmidt number is usually suggested a value ranging from 0.35 to 0.7. In the physics interface the default value is 0.35. The so-called drift velocity is included in Equation 6-47 as a diffusion term
Similarly, the number density equation (used to compute the interfacial area) for turbulent flow corresponds to
The inclusion of the drift velocity in Equation 6-47 modifies the flux of the dispersed phase. The effective dispersed phase flux jd,eff and velocity ud,eff are given by
jd,eff and ud,eff are available in the physics interface as mm.jdEff and mm.udEff.