2.3.7 DEFINE_EMISSIVITY_WEIGHTING_FACTOR

Description

When employing the non-gray discrete ordinates (DO) radiation model, you can use DEFINE_EMISSIVITY_WEIGHTING_FACTOR to modify the emissivity weighting factor $F(0 \rightarrow n\lambda_2 T) - F(0 \rightarrow n \lambda_1 T)$. By default, the emissivity weighting factor is calculated internally by ANSYS FLUENT so it can be used in the emission term of the radiative transfer equation, as shown in this equation in the separate Theory Guide . This macro allows you to revise the calculated value.

Usage

DEFINE_EMISSIVITY_WEIGHTING_FACTOR( name, c, t, T, nb, emissivity_weighting_factor)

Argument Type	Description
symbol name	UDF name.
cell_t c	Cell index.
Thread *t	Pointer to cell thread.
real T	Temperature.
int nb	Band number
real *emissivity_weighting_factor	The emissivity weighting factor in the emission
	term of the RTE for the non-gray DO model
	( this equation in the separate Theory Guide ).
Function returns
void

There are six arguments to DEFINE_EMISSIVITY_WEIGHTING_FACTOR: name, c, t, T, nb, emissivity_weighting_factor. You supply name, the name of the UDF. c, t, T, nb, and emissivity_weighting_factor are variables that are passed by the ANSYS FLUENT solver to your UDF. DEFINE_EMISSIVITY_WEIGHTING_FACTOR is called by ANSYS FLUENT for each cell.

Example

In the following UDF (named em_wt), the emissivity weighting factor present in the emission term of the RTE for the non-gray DO model is modified. The UDF is called for all of the cells. It modifies the emissivity weighting factor so that it is no longer the value calculated internally by ANSYS FLUENT, but is instead changed to $1$.

/* UDF to alter the emissivity weighting factor for the non-gray DO model */ 

#include "udf.h"

DEFINE_EMISSIVITY_WEIGHTING_FACTOR(em_wt,c,t,T,nb,emissivity_weighting_factor)
{

   /* revise the calculated emissivity_weighting_factor to be a value of 1  */

   *emissivity_weighting_factor = 1.0;

}

Hooking a Emissivity Weighting Factor UDF to ANSYS FLUENT

After the UDF that you have defined using DEFINE_EMISSIVITY_WEIGHTING_FACTOR is interpreted (Chapter  4) or compiled (Chapter  5), the name of the argument that you supplied as the first DEFINE macro argument (e.g., em_wt) will become visible and selectable in the User-Defined Function Hooks dialog box in ANSYS FLUENT. See Section  6.2.7 for details.