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23.12.3 Modeling Turbulence

If you are using the Eulerian model to solve a turbulent flow, you will need to choose one of turbulence models described in Section  23.5.10 in the Viscous Model panel (Figure  23.12.4).

Figure 23.12.4: The Viscous Model Panel for an Eulerian Multiphase Calculation
figure

The procedure is as follows:

1.   Select either k-epsilon or Reynolds Stress under Model.

2.   Select the desired k-epsilon Model or RSM Multiphase Model and any other related parameters, as described for single-phase calculations in Section  12.12.

3.   Under k-epsilon Multiphase Model or RSM Multiphase Model, indicate the desired multiphase turbulence model (see Section  23.5.10 for details about each):

  • Select Mixture to use the mixture turbulence model. This is the default model.

  • Select Dispersed to use the dispersed turbulence model. This model is applicable when there is clearly one primary continuous phase and the rest are dispersed dilute secondary phases.

  • Select Per Phase to use a $k$- $\epsilon$ turbulence model for each phase. This model is appropriate when the turbulence transfer among the phases plays a dominant role.



Including Source Terms


By default, the interphase momentum, $k$, and $\epsilon$ sources are not included in the calculation. If you want to include any of these source terms, you can enable them using the multiphase-options command in the define/models/viscous/multiphase-turbulence/ text menu. Note that the inclusion of these terms can slow down convergence noticeably. If you are looking for additional accuracy, you may want to compute a solution first without these sources, and then continue the calculation with these terms included. In most cases these terms can be neglected.



Customizing the $k$- $\epsilon$ Multiphase Turbulent Viscosity


If you are using the $k$- $\epsilon$ multiphase turbulence model, a user-defined function can be used to customize the turbulent viscosity for each phase. This option will enable you to modify $\mu_{\rm t}$ in the $k$- $\epsilon$ model. For more information, see the separate UDF Manual. In the Viscous Model panel, under User-Defined Functions, select the appropriate user-defined function in the Turbulent Viscosity drop-down list.


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