2.3.6 DEFINE_DOM_SPECULAR_REFLECTIVITY

Description

You can use DEFINE_DOM_SPECULAR_REFLECTIVITY to modify the inter-facial reflectivity of specularly reflecting semi-transparent walls. You may wish to do this if the reflectivity is dependent on other conditions that the standard boundary condition doesn't allow for (see this section in the separate Theory Guide for more information). During ANSYS FLUENT execution, the same UDF is called for all the faces of the semi-transparent wall, for each of the directions.

Usage

DEFINE_DOM_SPECULAR_REFLECTIVITY( name, f, t, nband, n_a, n_b, ray_direction, en,

internal_reflection, specular_reflectivity, specular_transmissivity)

Note that all of the arguments to a DEFINE macro need to be placed on the same line in your source code. Splitting the DEFINE statement onto several lines will result in a compilation error.

Argument Type	Description
symbol name	UDF name.
face_t f	Face index.
Thread *t	Pointer to face thread on which the specular
	reflectivity function is to be applied.
int nband	Band number (needed for non-gray discrete
	ordinates (DO) model).
real n_a	Refractive index of medium a.
real n_b	Refractive index of medium b.
real ray_direction	Direction vector ( $s$) defined
	in this equation in the separate Theory Guide
real en	Interface normal vector ( $n$) defined
	in this equation in the separate Theory Guide
int internal_reflection	Variable used to flag the code that total
	internal reflection has occurred.
real *specular_reflectivity	Specular reflectivity for the given direction $s$.
real *specular_transmissivity	Specular transmissivity for the given direction $s$.
Function returns
void

There are eleven arguments to DEFINE_DOM_SPECULAR_REFLECTIVITY: name, f, t, nband, n_a, n_b, ray_direction, en, internal_reflection, specular_reflectivity, and specular_transmissivity. You supply name, the name of the UDF. f, t, nband, n_a, n_b, ray_direction, en, internal_reflection, specular_reflectivity, and specular_transmissivity are variables that are passed by the ANSYS FLUENT solver to your UDF.

Example

In the following UDF, named user_dom_spec_refl, specular reflectivity and transmissivity values are altered for a given ray direction $s$ at face f.

Note that in the example that follows, the DEFINE_DOM_SPECULAR_REFLECTIVITY statement is broken up into three lines for the sake of readability. In your source file, you must make sure that the DEFINE statement is on one line only.

/*  UDF to alter the specular reflectivity and transmissivity, at
    semi-transparent walls, along direction s at face f */ 

#include "udf.h"

DEFINE_DOM_SPECULAR_REFLECTIVITY(user_dom_spec_refl,f,t, nband,n_a,n_b,
ray_direction,en,internal_reflection,specular_reflectivity, 
specular_transmissivity)
{
   real angle, cos_theta;
   real PI = 3.141592;
   cos_theta = NV_DOT(ray_direction, en);
   angle = acos(cos_theta);
   if (angle >45   && angle < 60)
     {
       *specular_reflectivity = 0.3;
       *specular_transmissivity = 0.7;
     }
}

Hooking a Discrete Ordinates Model (DOM) Specular Reflectivity UDF to ANSYS FLUENT

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

See Section  6.2.6 for details.