### 7.12.1. Phase-Dependent Turbulence Models

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.

#### 7.12.1.1. Algebraic Models

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 Equation` turbulence 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.

#### 7.12.1.2. Two Equation Models

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.

#### 7.12.1.3. Reynolds Stress Models

The multiphase versions of Reynolds stress models are equivalent to the single phase version.

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