19.4 Enabling the Eulerian 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 Eulerian under PDF Transport Options.

Figure 19.4.1: The Species Model Dialog Box for Eulerian Composition PDF Transport

2.   Enable Volumetric under Reactions. The Stiff Chemistry Solver is disabled by default and should be enabled if the kinetic mechanism is numerically stiff.

3.   Click the Integration Parameters... button to open the Integration Parameters dialog box (Figure  19.3.2). See Section  19.3.1 for detailed information about this dialog box.

4.   Enable Inlet Diffusion to include the diffusive transport of species through the inlets of your domain. Disable this option if the convective flux at one of the inlets is very small, resulting in mass loss by diffusion through that inlet.

5.   Make sure that Diffusion Energy Source is enabled if you want to include species diffusion effects in the energy equation.

6.   Enable Liquid Micro-Mixing if the fuel and oxidizer are liquids with low diffusivities (high Schmidt numbers). In this case, The Mixing Constant will be calculated per this equation in the separate Theory Guide.

7.   By default, the Laminar (one mode) energy equation is solved, where temperature fluctuations are ignored. By enabling Include Temperature Fluctuations, the multi-mode energy equation will be solved as done for species.

8.   In the Mixing tab, only the IEM mixing model is available for Eulerian PDF transport.

(a)   Specify the value of the Mixing Constant. The default value is 2 for gas phase species.

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

(b)   Enter the number of Flow Iterations per Chemistry Update. This is the frequency at which ANSYS FLUENT will update the chemistry during the calculation. Increasing the number can reduce the computational expense of the chemistry calculations.

(c)   Enter the 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.

9.   In the Boundary tab, define the compositions of the fuel and oxidizer.