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Define_source macro fluent udf

Hello experts!

Hope you are all fine. i am in need to take guidance regarding a small UDF which i wrote to add a source term. Actually i am working on transient Multiphase Eulerian model with one primary phase and one secondary phae. i have deactivated built in gravity and want to introduce a source term in y-momentum equation of secondary phase. Here is my UDF for the said purpose

#include "udf.h"

DEFINE_SOURCE(gravity_source,c,t,dS,eqn)
{
real gravity;
real source;
real density;
Thread *subthread;
subthread=THREAD_SUB_THREAD(t,1);
gravity = 9.8;
density=1000.0;
source = gravity*density*C_VOF(c,subthread);
dS[eqn] = 0.0;
return source;
}

that is, source=gravity x density x volume fraction of secondary phase.

but when i interpret/compile it with FLUENT i receive "Segmentation fault" error due to the presence of term "C_VOF(c,subthread)"
i run my UDF without this term and it runs fine. but i have to use this term to extract the volume fraction in the cell.

if you know where i am at fault please let me know, much appreciated.
Thanks in anticipation.

This should have been posted in FLUENT UDF forum.

I think your DEFINE_SOURCE is passing the primary phase thread and not the mixture one so that THREAD_SUB_THREAD is not doing what you expect.

Code:

#include "udf.h"



DEFINE_SOURCE(gravity_source,c,t,dS,eqn)

{

   real gravity, source, density;

   Thread *tm, *ts;  /* mixture and secondary thread */



   tm = THREAD_SUPER_THREAD(t);  /* get mixture thread */

   ts = THREAD_SUB_THREAD(tm,1); /* get secondary thread */



   gravity = 9.8;

   density=1000.0;

   source = gravity*density*C_VOF(c,ts);

   dS[eqn] = 0.0;



   return source;

}