Phase dependent turbulence models can be used in conjunction with the
inhomogeneous model (particle and mixture models) only. Each phase can use a
different turbulence model. All models available for single-phase calculations are
also available for continuous phases in multiphase calculations, with the exception
of the LES model. The models available for dispersed phases are limited to the
laminar model or zero equations models because other models are not considered to be
appropriate. For example, a recommended model for dilute dispersed two-phase flow
uses a two-equation model, such as the SST model or 
model, for the continuous phase, and an
algebraic eddy viscosity model for the dispersed phase, which simply sets the
dispersed phase viscosity proportional to the continuous phase eddy
viscosity.
For flows where the phases tend to separate, homogeneous turbulence is recommended. See the sections below for details.
If using the zero-equation algebraic turbulence model, there are several options:
The default zero-equation model uses a formula based on geometric length scale and the mean solution velocity. This should be used with caution for multiphase flow, as it is correlated for single-phase turbulent pipe flow.
You may supply your own prescription for eddy viscosity, using a constant or an expression.
For dispersed phases only, you may invoke the
Dispersed Phase Zero Equationturbulence model. This is the recommended algebraic model for a dispersed phase. It is only available for the disperse fluid when the continuous fluid is set to use a turbulence model (that is, not laminar).An Eddy Viscosity Prandtl Number can be specified. The default value of 1 is appropriate for bubbles or very small solid particles. For large solid particles in a gas phase is may be better to use a value greater than 1. This is highly model dependent. Several models are available in the literature.
The 
model in multiphase is very similar to the single-phase model.
It is recommended for use in continuous phases. The other two equation
turbulence models can be used for continuous phases, if desired.