[Shehryar]

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.

[Kimia]

Hi,

First of all your UDF compiles just fine if you compile it and not interpret it.
Second, in the Eulerian multiphase model, you have access to the momentum source terms in primary and secondary phase zones and not the mixture.
The thread you are calling is the mixture thread. You don't need to do that. You can just add the source term through the cell zone conditions>secondary zone> Source terms> Y momentum
I think your UDF should directly be added to your secondary phase and be like this:

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

You can call the density as well by C_R(c,t).

I hope this helps.

[Shehryar]

Thank you very much for the reply
But if i use C_VOF(c,t) then its sure i am getting volume fraction of secondary phase? By using

subthread=THREAD_SUB_THREAD(t,1);
C_VOF(c,subthread)

i was trying to get the volume fraction of secondary phase.

[Shehryar]

i have compiled and added the source term in momentum equation of secondary phase. it runs fine. but i am still confused if C_VOF(c,t) is giving me the volume fraction of secondary phase or not.

[Kimia]

When you add the source term to the secondary phase, by default the threads that are passed on by FLUENT are phase level threads from that specific phase. so t here is pointer to secondary phase threads.
If however you want to a add a source term to the mixture phase and you want the volume fraction of the secondary phase you need to include THREAD_SUB_THREAD.

[Shehryar]

Perfect. i got it. i run the UDF using C_VOF(c,t) and its running successfully. Thanks a lot mate.

[daliyou]

Originally Posted by Kimia

When you add the source term to the secondary phase, by default the threads that are passed on by FLUENT are phase level threads from that specific phase. so t here is pointer to secondary phase threads.
If however you want to a add a source term to the mixture phase and you want the volume fraction of the secondary phase you need to include THREAD_SUB_THREAD.

Hello Guys,

I would like to add a source term (turbulence energy) to mixture phase. I need the velocity of the primary and secondary phase. I define as following after reading your post and other suggest:

DEFINE_SOURCE(Gb, c, phase_t, dS, eqn)
{
real Cb, U_rel_x, U_rel_y, U_rel, U_r, source;
real rho_c, rho_d, delta_rho;
const real g_force = 9.81;
Thread *thread_c,*thread_d,*mt;
Thread **all_phase_t; /*array*/
mt=THREAD_SUPER_THREAD(phase_t);
all_phase_t=THREAD_SUB_THREADS(mt);
thread_c = all_phase_t[0]; /*THREAD_SUB_THREAD(mt, 1); THREAD_SUB_THREAD(mix_thread, WATER_ID); liquid phase */
thread_d = all_phase_t[1]; /*THREAD_SUB_THREAD(mix_thread, AIR_ID); gas phase */
U_rel_x = C_U(c, thread_d) - C_U(c, thread_c);
U_rel_y = C_V(c, thread_d) - C_V(c, thread_c);
U_r = sqrt(U_rel_x*U_rel_x + U_rel_y*U_rel_y); /* relative velocity from udf */
/* U_r=sqrt(pow(U_rel_x,2.0)+pow(U_rel_y,2.0))*/
Cb= 0.8;
rho_c = C_R(c, thread_c); /* water density */
rho_d = C_R(c, thread_d); /* air density */
delta_rho = rho_c - rho_d; /* delta rho */
source= Cb*C_MU_L(c,phase_t)/C_MU_EFF(c,phase_t)*delta_rho*g_force*C_VOF(c,phas e_t)*U_r;*/
dS[eqn]= 0.0;
return source;
}

When hooking to fluent, there is no compiler error and some errors for calculating, as foolowing:
999999 (..\src\mpsystem.c@1172): mpt_read: failed: errno = 10054
999999: mpt_read: error: read failed trying to read 4 bytes: Invalid argument
MPI Application rank 0 exited before MPI_Finalize() with status -1073741819


I tried to fix it line by line, the problem is
'thread_c = all_phase_t[0];'

Can you give me some suggests? Thanks a lot!

Best regards
Dali