[AdrianoSilvares]

Hi community,

I am trying to simulate a medium that only absorbs radiation, which is enclosed by an annular space. The boundary condition is set at the inner wall in w/m2 and the medium has a defined absorption coefficient.
The medium absorbs radiation and undergo a chemical reaction, therefore I need to know how much radiation is absorbed within each finite volume.
Working with UDF I can access C_DO_I(c,t,i), F_DO_I(f,t,i) and C_DO_IRRAD(c,t,nb) variables, which seem to represent the discretized transmitted radiation beam at cell centers and faces and the total radiation transmitted at cell center for a given wavelengths respectively. Is that right? If so, should the former to variables be related to the third one? How? Also, if these values represent transmitted radiation in w/m2 that are reaching points in the finite volume, how can I calculate the absorbed radiation w/m3 for the same finite volume?

Below I pasted the UDF used to print above mentioned variables. The beam discretization is very coarse and counts only with 4 values.


DEFINE_ON_DEMAND(printI)
{
FILE *intcell;
FILE *intface;
Domain *d;
Thread *t;
Thread *tf;
cell_t c;
cell_t c_out;
face_t f;
int i = 0;
double xc[ND_ND];
double xf[ND_ND];
double I0, I1, I2, I3, If0, Inb0, If1, If2, If3;
int zone_ID;
d = Get_Domain(1);
intcell = fopen("Exportedintcell.txt", "w");
intface = fopen("Exportedintface.txt", "w");
thread_loop_c(t, d)
{
begin_c_loop(c, t) // loop over all cells
{
zone_ID = THREAD_ID(t); //
C_CENTROID(xc, c, t);
I0 = C_DO_I(c, t, 0); // Intensity
I1 = C_DO_I(c, t, 1); // Intensity
I2 = C_DO_I(c, t, 2); // Intensity
I3 = C_DO_I(c, t, 3); // Intensity
Inb0 = C_DO_IRRAD(c, t, 0);
fprintf(intcell, "%e\t%e\t%e\n", xc[0], xc[1], I0);
fprintf(intcell, "%e\t%e\t%e\n", xc[0], xc[1], I1);
fprintf(intcell, "%e\t%e\t%e\n", xc[0], xc[1], I2);
fprintf(intcell, "%e\t%e\t%e\n", xc[0], xc[1], I3);
fprintf(intcell, "%e\t%e\t%e\n", xc[0], xc[1], Inb0);
}
end_c_loop(c, t)
}
// FACE DATABASE
thread_loop_f(tf, d)
{

begin_f_loop(f, tf)
{
zone_ID = THREAD_ID(tf);
F_CENTROID(xf, f, tf);
if (BOUNDARY_FACE_THREAD_P(tf))
// face on the boundary
{
If0 = F_DO_I(f, tf, 0);
If1 = F_DO_I(f, tf, 1);
If2 = F_DO_I(f, tf, 2);
If3 = F_DO_I(f, tf, 3);
fprintf(intface, "%e\t%e\t%e\t%en", xf[0], xf[1], xf[2], If0);
fprintf(intface, "%e\t%e\t%e\t%en", xf[0], xf[1], xf[2], If1);
fprintf(intface, "%e\t%e\t%e\t%en", xf[0], xf[1], xf[2], If2;
fprintf(intface, "%e\t%e\t%e\t%en", xf[0], xf[1], xf[2], If3);
}
else
// internal face
{
fprintf(intface, "%e\t%e\t%e\t%en", xf[0], xf[1], xf[2], If0);
fprintf(intface, "%e\t%e\t%e\t%en", xf[0], xf[1], xf[2], If1);
fprintf(intface, "%e\t%e\t%e\t%en", xf[0], xf[1], xf[2], If2);
fprintf(intface, "%e\t%e\t%e\t%en", xf[0], xf[1], xf[2], If3);

}
}
end_f_loop(f, tf)

}
fclose(intcell);
fclose(intface);
}

[AdrianoSilvares]

It seems that even though you solve a DO non-gray model, Fluent still find a solution for DO gray model and C_DO_I(c,t,i) and F_DO_I(f,t,i) would be values calculated as solution.
In fluent theory user guide it is said that:"In the case of the non-gray model, 4NϴNφ or 8NϴNφ equations are solved for each band."
I understand that C_DO_IRRAD(c,t,nb) would be the net incident radiation for a given band stored at cell centroid and nb argument points to a specific band (ex. nb = 0 and nb = 1 are the first and second band defined).
If this is right, how could you access the discretized transmitted radiation beam for each band at cell centroids and faces?
If someone has any idea, please share. Fluent user guide is very economic explaining the DO model calculations and variables.

[Kuljeet]

hi can you elaborate what the 'i' argument represent in C_DO_I(c,t,i).
i am trying to find intensity associated with each band for gray model. the ultimate goal is implement FSK in Fluent. if you have idea to implement these it will be great help.
-K

[AlexanderZ]

C_DO_I(c,t,i) gives the intensity of radiation in the cell in the direction i. The direction i is the normal direction of discrete ordinate.

[Kuljeet]

i am using this UDF to compute intensity associated with each face. but i am getting segmentation error.



#include "udf.h" //code to compute face radiation intensity

DEFINE_ON_DEMAND(printI)
{
Domain *domain;
FILE *intFace;
Thread *t;
face_t f;
int i;
intFace = fopen("intensity.txt", "w");

thread_loop_f(t, domain)
{

begin_f_loop(f, t) // loop over all face
{
printf("face=%d\n",f);
for (i=0; i<16; i++) // here 16 = 2x2 angular discritisation. we need genral expression for this along with how to access band intensity
fprintf(intFace, "%d\n", F_DO_I(f,t,i));
}
end_f_loop(f, t)
printf("\n next thread\n");
}
fclose(intFace);
}

[AlexanderZ]

The direction i is the normal direction of discrete ordinate.

i =0, 1, 2