19.3 Enabling the Lagrangian Composition PDF Transport Model

To enable the composition PDF transport model, select Composition PDF Transport in the Species Model dialog box (Figure  19.3.1).

Models Species Edit...

When you enable Composition PDF Transport, the dialog box will expand to show the relevant inputs.

1.   Select Lagrangian under PDF Transport Options.

Figure 19.3.1: The Species Model Dialog Box for Lagrangian Composition PDF Transport

2.   Enable Volumetric under Reactions.

3.   Click the Integration Parameters... button to open the Integration Parameters dialog box (Figure  19.3.2). For additional information, see Section  19.3.1.

Figure 19.3.2: The Integration Parameters Dialog Box

4.   Enable KINetics from Reaction Design to allow you to use reaction rates from Reaction Design's KINetics module, instead of the default ANSYS FLUENT reaction rates. ANSYS FLUENT's ISAT algorithm is employed to integrate these rates. Please refer to the KINetics for Fluent manual [ 2] from Reaction Design for details on the chemistry formulation options. For more information, or to obtain a license to use the Fluent/KINetics module, please contact Reaction Design at info@reactiondesign.com or +1 858-550-1920, or go to http://www.reactiondesign.com

5.   Enable Liquid Micro-Mixing to interpolate $C_{\phi}$ from turbulence models and scalar spectra, as noted in this section in the separate Theory Guide. This is applied to cases where reactions in liquids occur at low turbulence levels, among reactants with low diffusivities. Therefore, a default value of $C_{\phi} = 2$ may not be desirable, as it over-estimates the mixing rate.

6.   In the Mixing tab, select Modified Curl, IEM, or EMST under Mixing Model and specify the value of the Mixing Constant ( $C_\phi$ in this equation in the separate Theory Guide). For more information about particle diffusion, see this section in the separate Theory Guide.

If the Liquid Micro-Mixing option is enabled, you cannot set the Mixing Constant.

7.   You will not be specifying species boundary conditions in the Boundary tab. This is only applicable to the Eulerian PDF Transport Option.

8.   In the Control tab, you will specify the Lagrangian PDF transport control parameters.

Particles Per Cell   sets the number of PDF particles per cell. Higher values of this parameter will reduce statistical error, but increase computational time.

Local Time Stepping   is available for steady-state simulations and can increase the convergence rate by taking maximum allowable time-steps on a cell-by-cell basis. (see this equation in the separate Theory Guide). If Local Time Stepping is enabled, then you can specify the following parameters:

Convection #   specifies the particle convection number (see $\Delta t_{\rm conv}$ in this equation in the separate Theory Guide).

Diffusion #   specifies the particle diffusion number (see $\Delta t_{\rm diff}$ in this equation ).

Mixing #   specifies the particle mixing number (see $\Delta t_{\rm mix}$ in this equation ).