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18.3 Steps for Using the Composition PDF Transport Model

The procedure for setting up and solving a composition PDF transport problem is outlined below, and then described in detail. Remember that only steps that are pertinent to composition PDF transport modeling are shown here. For information about inputs related to other models that you are using in conjunction with the composition PDF transport model, see the appropriate sections for those models.

1.   Read a CHEMKIN-formatted gas-phase mechanism file and the associated thermodynamic data file in the CHEMKIN Mechanism panel (see Section  14.1.9).

File $\rightarrow$ Import $\rightarrow$ CHEMKIN Mechanism...

figure   

If your chemical mechanism is not in CHEMKIN format, you will have to enter the mechanism into FLUENT as described in Section  14.1.2.

2.   Enable a turbulence model.

Define $\rightarrow$ Models $\rightarrow$ Viscous...

3.   Enable the Composition PDF Transport model and set the related parameters.

Define $\rightarrow$ Models $\rightarrow$ Species $\rightarrow$ Transport & Reaction...

4.   Check the material properties in the Materials panel and the reaction parameters in the Reactions panel. The default settings should be sufficient.

Define $\rightarrow$ Materials...

5.   Set the operating conditions and boundary conditions.

Define $\rightarrow$ Operating Conditions...

Define $\rightarrow$ Boundary Conditions...

6.   Check the solver settings.

Solve $\rightarrow$ Controls $\rightarrow$ Solution...

The default settings should be sufficient, although it is recommended to change the discretization to second-order once the solution has converged.

7.   Initialize the solution. You may need to patch a high-temperature region to ignite the flame.

Solve $\rightarrow$ Initialize $\rightarrow$ Initialize...

Solve $\rightarrow$ Initialize $\rightarrow$ Patch...

8.   Run the solution.

Solve $\rightarrow$ Iterate...

9.   Solve the problem and perform postprocessing.

figure   

A good initial condition can reduce the solution time substantially. It is recommended to start from an existing solution calculated using the EDC model, non-premixed combustion model, or partially premixed combustion model. See Chapters  14, 15, and 17 for further information on such simulations.

This procedure is demonstrated in the PDF transport tutorial, which is available at the Fluent User Services Center.




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