[Alex90]

Hello everybody,

as I am still quite new to UDF-scripting I do have problems creating a UDF for a variable heat source term.

Here is my issue. I have three coincident cylinders which do have the same axial length. The middle cylinder is my heat source. For my problem I assume a axial profile for the heat power Q, which means Q changes with z. This results in a heat source profile in z direction.

I want to define a UDF which tells Fluent, that my heat source term changes due to z.

Here is what I wrote so far:

#include "udf.h"

DEFINE_PROFILE(heatsource,c,t,dS,eqn)
{
real x[ND_ND];
real source;
real vol;
VOL = 1.256637061*10^(-5);
begin_f_loop(x,c,t)
{
F_CENTROID(x,c,t);
if(x[2] <= 0.300)
source(x,c,t) = 0;
else if(x[2] <= 0.600 && x[2] > 0.300)
source(x,c,t) = 3500.955/VOL;
else if(x[2] <= 1.050 && x[2] > 0.600)
source(x,c,t) = 4738.666/VOL;
else if(x[2] <= 2.100 && x[2] > 1.050)
source(x,c,t) = 4971.053/VOL;
else if(x[2] <= 2.850 && x[2] > 2.100)
source(x,c,t) = 5092.298/VOL;
else if(x[2] <= 3.300 && x[2] > 2.850)
source(x,c,t) = 4738.666/VOL;
else if(x[2] <= 3.600 && x[2] > 3.300)
source(x,c,t) = 3500.955/VOL;
else if(x[2] <= 3.900 && x[2] > 3.600)
source(x,c,t) = 2121.791/VOL;
else
source(x,c,t) = 0;
}
end_f_loop(x,c,t);
}

So far this does not work. Where is the Problem? I wrote a UDF for a profile of q which worked that way.

Thank you for any Help. ....

[upeksa]

1) VOL = 1.256637061*10^(-5) is wrong
real VOL = 1.256637061e-5 is correct

2) "real source" means a real variable, source(x,c,t) is a function you haven't defined anywhere.

3) is not DEFINE_PROFILE, is DEFINE_SOURCE

4) DEFINE_SOURCE macro has implicit a loop over cells (check the arguments). If you are also looping over faces, the code will loop over all faces in every cell. The computational cost will be huge.

5) DEFINE_SOURCE needs a "return"

6) "dS" and "eqn" must be defined somewhere, as "dS[eqn] =0.0" at least

I guess I am even missing something

[Alex90]

Hi,
sorry that my answer took so long ...

I tried to insert the changes you suggested, though I am not quite sure if thats totally correct now. Besides I get an Error when I am interpreting it within FLUENT, it tells me that in line 15 (which is the line with source(x,c,t)=0 ''no function prototype'' ? What does that mean ? ...

As I said earlier I am completly new to UDF .... Thanks a lot for support.

#include "udf.h"

DEFINE_SOURCE(heatsource,c,t,dS,eqn)
{
real x[ND_ND];
real source;
real VOL;
real Q;

VOL = 1.256637061e-5;

C_CENTROID(x,c,t);
if(x[2] <= 0.300)
{
source(x,c,t) = 0;
}
else if(x[2] <= 0.600 && x[2] > 0.300)
{
source(x,c,t) = 1.309/VOL;
}
else if(x[2] <= 1.050 && x[2] > 0.600)
{
source(x,c,t) = 2.659/VOL;
}
else if(x[2] <= 2.100 && x[2] > 1.050)
{
source(x,c,t) = 6.508/VOL;
}
else if(x[2] <= 2.850 && x[2] > 2.100)
{
source(x,c,t) = 4.762/VOL;
}
else if(x[2] <= 3.300 && x[2] > 2.850)
{
source(x,c,t) = 2.659/VOL;
}
else if(x[2] <= 3.600 && x[2] > 3.300)
{
source(x,c,t) = 1.309/VOL;
}
else if(x[2] <= 3.900 && x[2] > 3.600)
{
source(x,c,t) = 0.794/VOL;
}
else
{
source(x,c,t) = 0;
}

return source;
}

[Alex90]

Hey there,

i tried to make this udf work, I really need it as I am writing my final thesis at university right now.

So here is the CODE I am using currently.

#include "udf.h"
#define PI 3.14159265


DEFINE_SOURCE(WQuelle,c,t,dS,eqn)
{
real x[ND_ND];
real vol, source;

C_CENTROID(x,c,t)

vol = PI*0.25*0.004*0.004*x[2]

if(x[2] <= 0.300)
source =0;
else if(x[2] <= 0.600 && x[2] > 0.300)
source = 1.309/vol;
else if(x[2] <= 1.050 && x[2] > 0.600)
source = 2.6587/vol;
else if(x[2] <= 2.100 && x[2] > 1.050)
source = 6.5079/vol;
else if(x[2] <= 2.850 && x[2] > 2.100)
source = 4.7619/vol;
else if(x[2] <= 3.300 && x[2] > 2.850)
source = 2.6587/vol;
else if(x[2] <= 3.600 && x[2] > 3.300)
source = 1.3095/vol;
else if(x[2] <= 3.900 && x[2] > 3.600)
source = 0.7936/vol;
else
source = 0;

dS[eqn]=0;

return source;
}

I am trying to interpret it with FLUENT. But I get the following failure.

Error: C:/Users/LOCAL_~1/AppData/Local/Temp/HeatSource.c.22320.3.c: line 14: parse error.
Error: C:/Users/LOCAL_~1/AppData/Local/Temp/HeatSource.c.22320.3.c: line 16: parse error.
Error: C:/Users/LOCAL_~1/AppData/Local/Temp/HeatSource.c.22320.3.c: line 18: parse error.
Error: C:/Users/LOCAL_~1/AppData/Local/Temp/HeatSource.c.22320.3.c: line 20: parse error.
Error: C:/Users/LOCAL_~1/AppData/Local/Temp/HeatSource.c.22320.3.c: line 22: parse error.
Error: C:/Users/LOCAL_~1/AppData/Local/Temp/HeatSource.c.22320.3.c: line 24: parse error.
Error: C:/Users/LOCAL_~1/AppData/Local/Temp/HeatSource.c.22320.3.c: line 26: parse error.
Error: C:/Users/LOCAL_~1/AppData/Local/Temp/HeatSource.c.22320.3.c: line 28: parse error.
Error: C:/Users/LOCAL_~1/AppData/Local/Temp/HeatSource.c.22320.3.c: line 30: parse error.

I tried to figure that out, but somehow I really do not quite understand where the problem is. If anyone is able to help ... i would appreciate it ...
Thanks alot ... Alex