[CFD27]

Hello all,
I have a problem in defining diffusivity. I want to define two different diffusion coefficients in two different cell zones. For this I use the following UDF:

DEFINE_DIFFUSIVITY(diffusion, c, t, i)
{
	Domain* d;
	Thread * tc1, * tc2;

	d = Get_Domain(1);
	
	tc1 = Lookup_Thread(d, 8);
	tc2 = Lookup_Thread(d, 9);


	if (t == tc1)
	{
		diffusivity = 1e-7;
	}
	else if (t == tc2)
	{
		diffusivity = 1e-5;
	}
	return diffusivity;
	
}

The UDF compiles without any problems. However, you can see in the post that the diffusion coefficients are not inserted correctly. Does anyone have an idea what this can be due to?
Many thanks in advance.
Many greetings
Joe

[AlexanderZ]

plot contour from 1e-7 to 1e-4
turn of node values in contours options

[CFD27]

Dear Alexander,
Thank you very much for your answer. I followed your tips, but I didn't know what to do with your second tip. I now have the Contour displayed in range from 1e-7 to 1e-4 and have changed the Location variable from Vertex to Face. Unfortunately, this did not change much.
Many thanks in advance.
Joe

[AlexanderZ]

I thought it was the problem of plotting, which isn't

so you should compile the code.
variable diffusivity was not defined

#include "udf.h"
DEFINE_DIFFUSIVITY(diffusion, c, t, i)
{
	Domain* d;
	Thread * tc1, * tc2;
	real diffusivity;
	d = Get_Domain(1);	
	tc1 = Lookup_Thread(d, 8);
	tc2 = Lookup_Thread(d, 9);
	if (t == tc1)
	{
		diffusivity = 1e-7;
	}
	else if (t == tc2)
	{
		diffusivity = 1e-5;
	}
	return diffusivity;	
}

I'm working inside fluent stand alone, making pictures there
for me it's strange to see on your picture name diffusivity under user defined variable 7
at least its a property of scalar

so first compile code and try again.
I'm assuming that 8 and 9 zones ate rectangular and circle from your picture

[CFD27]

Dear Alexander,

Thank you for your reply. I have already complicated the code. The diffusivity variable is defined as a global variable and therefore not seen in the code, please excuse me. I use the diffusivity in other UDF to define the laminar diffusion. There is a species source in the circle. These species must be transported across the circle wall using sinks and sources which are adjacent to the circle walls. The cell area in the circle has the cell thread 8 and the cells outside the circle has the cell area 9. I have saved the diffusivity in a UDM to be able to look at the values of this in postprocessing. Is there another way to view the values of diffusivity?
Many thanks in advance.
Many Greetings
Joe

[AlexanderZ]

diffusivity is applied in fluent as a material property
that's why you are using build in macro DEFINE_DIFFUSIVITY to define it

if you are saying that diffusivity is saved in a UDM somewhere else, probably that's an issue as variable "diffusivity" contains only only 1 value (not an array of values over all cells)

so to store diffusivity in UDM you may use this code ( i have no idea how you've made it, may be your way is correct either)

#include "udf.h"
DEFINE_DIFFUSIVITY(diffusion, c, t, i)
{
	Domain* d;
	Thread * tc1, * tc2;
	real diffusivity;
	d = Get_Domain(1);	
	tc1 = Lookup_Thread(d, 8);
	tc2 = Lookup_Thread(d, 9);
	if (t == tc1)
	{
		diffusivity = 1e-7;
	}
	else if (t == tc2)
	{
		diffusivity = 1e-5;
	}
esle
diffusivity = 0;
C_UDMI(c,t,0) = diffusivity;
	return diffusivity;	
}

[CFD27]

Dear Alexander,
Thank you very much for your reply. I have tried your code and it works. Previously I had saved the diffusivity in a Define on Demand macro in a UDM. Thank you very much for your help. However, I would have one more question. Is it necessary to use !RP_HOST in a Define Diffusivity macro? Thank you very much in advance.
Many greetings
Joe

[AlexanderZ]

you don't need it while you are not doing following:
• Reading and Writing Files
• Global Reductions
• Global Sums
• Global Minimums and Maximums
• Global Logicals
• Certain Loops over Cells and Faces
• Displaying Messages on a Console
• Printing to a Host or Node Process
• Reading/writing VP_VARs

[CFD27]

Thank you for your help.

Many Greetings
Joe