15.1.2 Enabling Species Transport and Reactions and Choosing the Mixture Material

The problem setup for species transport and volumetric reactions begins in the Species Model dialog box (Figure  15.1.1). For cases which involve multiphase species transport and reactions, refer to this section in the separate Theory Guide.

Models Species Edit...

Figure 15.1.1: The Species Model Dialog Box

1.   Under Model, select Species Transport.

2.   Under Reactions, enable Volumetric.

3.   In the Mixture Material drop-down list under Mixture Properties, choose which mixture material you want to use in your problem. The drop-down list will include all of the mixtures that are currently defined in the database. To check the properties of a mixture material, select it and click the Edit... button. If the mixture you want to use is not in the list, choose the mixture-template material, and see Section  15.1.3 for details on setting your mixture's properties. If there is a mixture material listed that is similar to your desired mixture, you may choose that material and see Section  15.1.3 for details on modifying properties of an existing material.

When you choose the Mixture Material, the Number of Volumetric Species in the mixture will be displayed in the dialog box for your information.

Note that if you re-open the Species Model dialog box after species transport has already been enabled, only the mixture materials available in your case will appear in the list. You can add more mixture materials to your case by copying them from the database, as described in Section  8.1.2, or by creating a new mixture, as described in Sections  8.1.2 and 15.1.3.

As mentioned in Section  15.1.1, modeling parameters for the species transport and (if relevant) reactions will automatically be loaded from the database. If any information is missing, you will be informed of this after you click OK in the Species Model dialog box. If you want to check or modify any properties of the mixture material, you will use the Create/Edit Materials dialog box, as described in Section  15.1.3.

4.   Choose the Turbulence-Chemistry Interaction model. Four models are available:

Laminar Finite-Rate   computes only the Arrhenius rate (see this equation in the separate Theory Guide) and neglects turbulence-chemistry interaction. You can specify the following inputs:

Flow Iterations per Chemistry Update   Increasing the number reduces the computational expense of the chemistry calculations. By default, ANSYS FLUENT will update the chemistry once per 10 flow iterations.

Aggressiveness Factor   This is a numerical factor which controls the robustness and the convergence speed. This value ranges between 0 and 1, where 0 (the default) is the most robust, but results in the slowest convergence.

Finite-Rate/Eddy-Dissipation   (for turbulent flows only) computes both the Arrhenius rate and the mixing rate and uses the smaller of the two.

Eddy-Dissipation   (for turbulent flows only) computes only the mixing rate (see this equation and this equation in the separate Theory Guide).

Eddy-Dissipation Concept   (for turbulent flows only) models turbulence-chemistry interaction with detailed chemical mechanisms (see this equation and this equation in the separate Theory Guide). When using this model, you can modify the following:

Flow Iterations per Chemistry Update   Increasing the number reduces the computational expense of the chemistry calculations. By default, ANSYS FLUENT will update the chemistry once per 10 flow iterations.

Aggressiveness Factor   This is a numerical factor which controls the robustness and the convergence speed. This value ranges between 0 and 1, where 0 (the default) is the most robust, but results in the slowest convergence.

Volume Fraction Constant   and the Time Scale Constant ( $C_{\xi}$ in this equation and $C_{\tau}$ in this equation in the separate Theory Guide), although the default values are recommended.

5.   You can set the integration parameters for the Laminar Finite-Rate and Eddy-Dissipation Concept models by clicking the Integration Parameters... button under Reactions. When using ISAT for chemistry tabulation, it is important to set appropriate maximum table size and error tolerance. For details about this option, see Section  19.2.

6.   (optional) If you want to model full multicomponent (Stefan-Maxwell) diffusion or thermal (Soret) diffusion, enable the Full Multicomponent Diffusion or Thermal Diffusion option.

See Section  8.9.2 for details.

7.   Enabling KINetics from Reaction Design for laminar reactions, will allow you to use the proprietary reaction-rate utilities and solution algorithms from Reaction Design, which is based on and compatible with their CHEMKIN technology [ 39]. For Eddy-Dissipation Concept Turbulence-Chemistry Interaction and the Composition PDF Transport model, enabling the KINetics from Reaction Design option will 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 the Fluent/KINetics module, please contact Reaction Design at info@reactiondesign.com or +1 858-550-1920, or go to http://www.reactiondesign.com