2.3.17 DEFINE_SCAT_PHASE_FUNC

Description

You can use DEFINE_SCAT_PHASE_FUNC to specify the radiation scattering phase function for the discrete ordinates (DO) model. The function computes two values: the fraction of radiation energy scattered from direction $i$ to direction $j$, and the forward scattering factor.

Usage

DEFINE_SCAT_PHASE_FUNC( name, cosine, f)

Argument Type	Description
symbol name	UDF name.
real cosine	Cosine of the angle between directions $i$ and $j$.
real *f	Pointer to the location in memory where the real forward
	scattering factor is stored.
Function returns
real

There are three arguments to DEFINE_SCAT_PHASE_FUNC: name, cosine, and f. You supply name, the name of the UDF. cosine and f are variables that are passed by the ANSYS FLUENT solver to your UDF. Your UDF will need to compute the real fraction of radiation energy scattered from direction $i$ to direction $j$ and return it to the solver. Note that the solver computes and stores a scattering matrix for each material by calling this function for each unique pair of discrete ordinates.

Example

In the following example, a number of UDFs are concatenated in a single C source file. These UDFs implement backward and forward scattering phase functions that are cited by Jendoubi et al. [ 5]. The source code can be interpreted or compiled in ANSYS FLUENT.

/*******************************************************************
   UDFs that implement backward and forward scattering            
   phase functions as cited by Jendoubi et. al.                     
********************************************************************/

#include "udf.h"

DEFINE_SCAT_PHASE_FUNC(ScatPhiB2,c,fsf) 
{
  real phi=0;
  *fsf = 0;
  phi = 1.0 - 1.2*c + 0.25*(3*c*c-1);
  return (phi);
}

DEFINE_SCAT_PHASE_FUNC(ScatPhiB1,c,fsf)
{
  real phi=0;
  *fsf = 0;
  phi = 1.0 - 0.56524*c + 0.29783*0.5*(3*c*c-1) +
    0.08571*0.5*(5*c*c*c-3*c) + 0.01003/8*(35*c*c*c*c-30*c*c+3) +
    0.00063/8*(63*c*c*c*c*c-70*c*c*c+15*c);
  return (phi);
}

DEFINE_SCAT_PHASE_FUNC(ScatPhiF3,c,fsf) 
{
  real phi=0;
  *fsf = 0;
  phi = 1.0 + 1.2*c + 0.25*(3*c*c-1);
  return (phi);
}

DEFINE_SCAT_PHASE_FUNC(ScatPhiF2,c,fsf)
{
  real phi=0;
  real coeffs[9]={1,2.00917,1.56339,0.67407,0.22215,0.04725,
                  0.00671,0.00068,0.00005};
  real P[9];
  int i;
  *fsf = 0;
  P[0] = 1;
  P[1] = c;
  phi = P[0]*coeffs[0] + P[1]*coeffs[1];
  for(i=1;i<7;i++)
    {
      P[i+1] = 1/(i+1.0)*((2*i+1)*c*P[i] - i*P[i-1]);
      phi += coeffs[i+1]*P[i+1];
    }
  return (phi);
}

DEFINE_SCAT_PHASE_FUNC(ScatIso,c,fsf) 
{
  *fsf=0;
  return (1.0);
}

Hooking a Scattering Phase UDF to ANSYS FLUENT

After the UDF that you have defined using DEFINE_SCAT_PHASE_FUNCTION is interpreted (Chapter  4) or compiled (Chapter  5), the name that you specified in the DEFINE macro argument (e.g., ScatPhiB) will become visible and selectable in the Create/Edit Materials dialog box in ANSYS FLUENT.
See Section  6.2.17 for details.