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8.8.2 Scattering Coefficient

The scattering coefficient is, by default, set to zero, and it is assumed to be isotropic. You can specify a constant value, a temperature-dependent function (see Section  8.2), or a user-defined function. You can also specify a non-isotropic phase function.

The scattering coefficient is requested in units of 1/length. Along with the absorption coefficient, it describes the change in radiation intensity per unit length along the path through the fluid medium. You may wish to increase the scattering coefficient in combustion systems, where particulates may be present.

Inputs for a Constant Scattering Coefficient

To define a constant scattering coefficient, simply enter the value in the field next to Scattering Coefficient in the Materials panel. (Select constant in the drop-down list first if it is not already selected.)

Inputs for the Scattering Phase Function

Scattering is assumed to be isotropic, by default, but you can also specify a linear-anisotropic scattering function. If you are using the DO model, Delta-Eddington and user-defined scattering functions are also available.

Isotropic Phase Function

To model isotropic scattering, select isotropic in the Scattering Phase Function drop-down list. No further inputs are necessary. This is the default setting in FLUENT.

Linear-Anisotropic Phase Function

To model anisotropic scattering, select linear-anisotropic in the Scattering Phase Function drop-down list and set the value of the phase function coefficient ( $C$ in Equation  13.3-3).

Delta-Eddington Phase Function

To use a Delta-Eddington phase function, select delta-eddington in the Scattering Phase Function drop-down list. This will open the Delta-Eddington Scattering Function panel,in which you can specify the Forward Scattering Factor and Asymmetry Factor ( $f$ and $C$ in Equation  13.3-46). Note that, since this is a modal panel, you must tend to it immediately.

User-Defined Phase Function

To use a user-defined phase function, select user-defined in the Scattering Phase Function drop-down list. The user-defined function must contain specifications for $\Phi^*$ and $f$ in Equation  13.3-47. See the separate UDF Manual for information about user-defined functions.

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