16.2.3 Enabling a Secondary Inlet Stream

If you are modeling a system consisting of a single fuel and a single oxidizer stream, you do not need to enable a secondary stream in your PDF calculation. As discussed in this section in the separate Theory Guide , a secondary stream should be enabled if your PDF reaction model will include any of the following:

• two dissimilar gaseous fuel streams
  • In these simulations, the fuel stream defines one of the fuels and the secondary stream defines the second fuel.

• mixed fuel systems of dissimilar gaseous and liquid fuel
  • In these simulations, the fuel stream defines the gaseous fuel and the secondary stream defines the liquid fuel (or vice versa).

• mixed fuel systems of dissimilar gaseous and coal fuels
  • In these simulations, you can use the fuel stream or the secondary stream to define either the coal or the gaseous fuel. See Section  16.4.5 regarding coal combustion simulations with the non-premixed combustion model.

• mixed fuel systems of coal and liquid fuel
  • In these simulations, you can use the fuel stream or the secondary stream to define either the coal or the liquid fuel. See Section  16.4.5 regarding coal combustion simulations with the non-premixed combustion model.

• coal combustion
  • Coal combustion can be more accurately modeled by using a secondary stream to track the distinct volatile and char off-gases. The fuel stream must define the char and the secondary stream must define the volatile components of the coal. See Section  16.4.5 regarding coal combustion simulations with the non-premixed combustion model.

• a single fuel with two dissimilar oxidizer streams
  • In these simulations, the fuel stream defines the fuel, the oxidizer stream defines one of the oxidizers, and the secondary stream defines the second oxidizer.

To include a secondary stream in your model, turn on the Secondary Stream option under Stream Options in the Chemistry tab.

Using a secondary stream can substantially increase the calculation time for your simulation since the multi-dimensional PDF integrations are performed at run-time. Alternatively, ANSYS FLUENT can perform a full tabulation of the PDF integrations, as detailed in Section  16.7.1.