[kawkab]

I'm new to using UDF and I'm trying to write source code to set a 2D Gaussian distribution for the radiation flux as a BC.

Here is a basic code I wrote but for some reason, it doesn't distribute the flux correctly.

# include <math.h>
#include "udf.h"

# define x_m 0
# define y_m 0
# define i_m 6750000

DEFINE_PROFILE(radiation_flux, thread, position)
{
int x[ND_ND]; /* this will hold the position vector */
face_t f;

begin_f_loop(f, thread)
{
F_CENTROID(x, f, thread);
F_PROFILE(f, thread, position) = i_m * exp(-1 * ((((x[0] - x_m) ^ 2) / 2) + (((x[1] - y_m) ^ 2) / 2)));
}
end_f_loop(f, thread)
}

[Svetlana]

Does it compile? Could you please attach a contour of the flux that you receive?

[AlexanderZ]

#include "udf.h"
must be in the first line

compile your code and read errors

[kawkab]

It's compiled without any error. I placed the #include "udf.h" in the first line but I still get a constant radiation intensity after initializing the solution (see attached image).

[AlexanderZ]

show exact code which you are using and which is compiled without errors from your point of view,
show compilation log

[kawkab]

The compilation log is as follows:

Copied C:\Workspace\Ansys\Steadyhalf_files\dp0\FFF-3\Fluent/C:\Workspace\Ansys\Steadyhalf_files\dp0\FFF-3\Fluent\Source2.c to libudf\src
Creating user_nt.udf file for 3d ...
(system "copy "C:\PROGRA~1\ANSYSI~1\v171\fluent"\fluent17.1.0\src\udf\makefile_nt.udf "libudf\win64\3d\makefile" ")
        1 file(s) copied.
(chdir "libudf")(chdir "win64\3d")# Generating ud_io1.h
Source2.c
# Generating udf_names.c because of makefile Source2.obj
udf_names.c
# Linking libudf.dll because of makefile user_nt.udf udf_names.obj Source2.obj
Microsoft (R) Incremental Linker Version 14.24.28314.0
Copyright (C) Microsoft Corporation.  All rights reserved.

   Creating library libudf.lib and object libudf.exp

Done.#

And the code is:

#include "udf.h"
# include <math.h>

# define x_m 0
# define y_m 0
# define stdv 5
# define i_m 6750000
# define M_PI 3.14159265358979323846

DEFINE_PROFILE(radiation, t, i)
{
	int x[ND_ND]; /* this will hold the position vector */
	face_t f;

	begin_f_loop(f, t)
	{
		F_CENTROID(x, f, t);
		F_PROFILE(f, t, i) = i_m * (exp(-1 * ((((x[0] - x_m) ^ 2) / 2) + (((x[1] - y_m) ^ 2) / 2))));
		/*F_PROFILE(f, t, i) = i_m*(1/(2*M_PI*stdv))*exp(-1*(((x[0]-x_m)^2+(x[1]-y_m)^2)/(2*stdv^2)));*/
	}
	end_f_loop(f, thread)
}

[kawkab]

The compilation log is:

 Copied C:\Workspace\Ansys\Steadyhalf_files\dp0\FFF-3\Fluent/C:\Workspace\Ansys\Steadyhalf_files\dp0\FFF-3\Fluent\Source2.c to libudf\src
Creating user_nt.udf file for 3d ...
(system "copy "C:\PROGRA~1\ANSYSI~1\v171\fluent"\fluent17.1.0\src\udf\makefile_nt.udf "libudf\win64\3d\makefile" ")
1 file(s) copied.
(chdir "libudf")(chdir "win64\3d")# Generating ud_io1.h
Source2.c
# Generating udf_names.c because of makefile Source2.obj
udf_names.c
# Linking libudf.dll because of makefile user_nt.udf udf_names.obj Source2.obj
Microsoft (R) Incremental Linker Version 14.24.28314.0
Copyright (C) Microsoft Corporation. All rights reserved.

Creating library libudf.lib and object libudf.exp

Done.

While the exact code is:

# #include "udf.h"
# include <math.h>

# define x_m 0
# define y_m 0
# define stdv 1
# define i_m 6750000
# define M_PI 3.14159265358979323846

DEFINE_PROFILE(radiation, t, i)
{
	int x[ND_ND]; /* this will hold the position vector */
	face_t f;

	begin_f_loop(f, t)
	{
		F_CENTROID(x, f, t);
		F_PROFILE(f, t, i) = i_m*(1/(2*M_PI*stdv))*exp(-1*(((x[0]-x_m)^2+(x[1]-y_m)^2)/(2*stdv^2)));
	}
	end_f_loop(f, t)
}

[kawkab]

Let me clarify what I'm actually doing. It's a 3D fluent case and I'm trying to impose radiation flux on a circular boundary (window) with a 2D Gaussian distribution.

I compiled the previous code as a UDF and used it as a BC for direct radiation for the window. After I initialized the solution, the radiation intensity on the window becomes constant. But after running the solution for a few iterations, it takes a strange distribution (see the front view in the attached image).

[AlexanderZ]

# include "udf.h"
# include <math.h>

# define x_m 0
# define y_m 0
# define stdv 1
# define i_m 6750000

DEFINE_PROFILE(radiation, t, i)
{
	int x[ND_ND]; /* this will hold the position vector */
	face_t f;

	begin_f_loop(f, t)
	{
		F_CENTROID(x, f, t);
		F_PROFILE(f, t, i) = i_m*(1/(2*M_PI*stdv))*exp(-1*((pow((x[0]-x_m),2)+pow((x[1]-y_m),2))/(2*pow(stdv,2))));
	}
	end_f_loop(f, t)
}