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Shekhar April 13, 2004 00:45

C_VOF_G works???
Does C_VOF_G works.....does it calculate the gradient vector of volume fraction of the phases...


FJ April 13, 2004 03:02

Re: C_VOF_G works???

Yes. It does work but you have to set the following in Fluent text prompt.

solve/set/expert/Keep temporary solver memory from being feed? : yes

Default is "no".

Thank you


Shekhar April 13, 2004 06:14

Re: C_VOF_G works???
Thanks FJ, I already did that but still when i start my iterations, this error comes:

Error: FLUENT received fatal signal (ACCESS_VIOLATION) 1. Note exact events leading to error. 2. Save case/data under new name. 3. Exit program and restart to continue. 4. Report error to your distributor. Error Object: ()


thomas April 13, 2004 06:25

Re: C_VOF_G works???
This macro seems to be restricted to the VOF model. Are you using the VOF model ? Thomas

shekhar April 13, 2004 08:53

Re: C_VOF_G works???
no thomas, i am using the eulerian multiphase model... actually i am adding the capillary pressure as a momentum source term in my multiphase flow problem, and there i need to compute the gradient of volume fractions of the is that possible with eulerian multiphase model !!!


thomas April 13, 2004 12:34

Re: C_VOF_G works???
I wouold suggest to write a UDS to store the VOF value and then you can get your VOF gradient using the command C_UDS_G.


FJ April 13, 2004 20:54

Re: C_VOF_G works???

I think all gradient macro doesn't have the values at first iteration. So at first iteration, you don't hook your function and the next iteration , let's hook it.

I think it will be O.K.

Thank you


Shekhar April 14, 2004 05:07

Re: C_VOF_G works???
Thanks FJ, I already tried that too....but this time there comes a different error: Error: divergence detected in AMG solver: pressure correction Error Object: ()


FJ April 14, 2004 22:48

Re: C_VOF_G works???

Oh, really?. If your UDF function is not called, is your calculation no problem?.

Thank you


Shekhar April 15, 2004 03:19

Re: C_VOF_G works???
thanks FJ, Ya there isnt any problem when i do not link the UDF. The problem only comes after linking the UDF. I guess its not calculating the gradient of the volume fractions. Well, I am pasting here the UDF as well. this UDF is for adding a momentum source term to phase (i am modeling the hydrodynamics of gas and liquid flow in a packed bed).

#include "udf.h"

DEFINE_SOURCE(cell_x_source, cell, thread_l, dS, eqn) { real source, thita_s, thita_g, rho_g, rho_l, n1, n2; Thread *mixture_thread = THREAD_SUPER_THREAD(thread_l); Thread **pt; pt = THREAD_SUB_THREADS(mixture_thread); thita_g = C_VOF (cell, pt[0]); thita_s = C_VOF (cell, pt[2]); rho_g = C_R (cell, pt[0]); rho_l = C_R (cell, pt[1]); n1 = C_VOF_G (cell, pt[0]) [0]; n2 = C_VOF_G (cell, pt[2]) [0]; source = 96.015*(pow((1-thita_g),0.5)/pow(thita_s,1.5)*n2 + 1/(pow(thita_s,0.5)*pow((1-thita_g),0.5))*n1); dS[eqn] = 0.0; return source; }

FJ April 15, 2004 21:49

Re: C_VOF_G works???

Year, I've got the same error as your remarks. I considered your UDF but I don't really understand why this kind of error is happened. So I re-coded with my way for unsteady calculation.It was O.K under my conditions.

#include "udf.h"


{ Thread *t; Thread **pt; cell_t c; Domain *domain = Get_Domain(1); real thita_s, thita_g, rho_g, rho_l, n1, n2;

mp_thread_loop_c (t,domain,pt)


begin_c_loop(c, t)


thita_s = C_VOF (c, pt[2]);

thita_g = C_VOF (c, pt[0]);

rho_g = C_R (c, pt[0]);

rho_l = C_R (c, pt[1]);

n1 = C_VOF_G (c, pt[0])[0];

n2 = C_VOF_G (c, pt[2])[0];

C_UDMI(c, t, 0) = thita_s;

C_UDMI(c, t, 1) = thita_g;

C_UDMI(c, t, 2) = rho_g;

C_UDMI(c, t, 3) = rho_l;

C_UDMI(c, t, 4) = n1;

C_UDMI(c, t, 5) = n2;

C_UDMI(c, t, 6) = 96.015*(pow((1-thita_g),0.5)/pow(thita_s,1.5)*n2

+ 1/(pow(thita_s,0.5)*pow((1-thita_g),0.5))*n1);

}end_c_loop(c, t)

} }

DEFINE_SOURCE(cell_x_source, c, t, dS, eqn) { real source;

source = C_UDMI(c, t, 6); dS[eqn] = 0.0;

return source; }

Thank you


shekhar April 16, 2004 05:50

Re: C_VOF_G works???
thanks FJ, i ll try it n let u know :)


Fourati April 5, 2012 08:48

Same problem
Hello, I am having the same error message when trying to hook a source term in liquid phase of gas/liquid flow that is function of C_VOF_G. Did you find what's going on with yours please ? Thanks

pannsave March 23, 2014 09:33

gradient of volume fraction in Euler-Euler
Hi Fourati,
I am having problem with the implementation of volume fraction gradient in E-E simulation for my source term in momentum equation.
I have used the following UDF to store my memory which is used for my source term calculation. When i run my simulation, the user defined memory shows always zero, which results zero in my source.
I would be thankful to you if you have any suggestion for my problem.
#include "udf.h"
#define CON1
DEFINE_ADJUST(myadjust,d){ if(ROOT_DOMAIN_P(d)){cell_t c;Thread *t;
Domain *sd = DOMAIN_SUB_DOMAIN(d,0); Alloc_Storage_Vars(sd,SV_VOF_RG,SV_VOF_G,SV_NULL); Scalar_Reconstruction(sd, SV_VOF,-1,SV_VOF_RG,NULL); Scalar_Derivatives(sd,SV_VOF,-1,SV_VOF_G,SV_VOF_RG,&Vof_Deriv_Accumulate);thread _loop_c(t,d)
{Thread *pt = THREAD_SUB_THREAD(t,0);
begin_c_loop(c,t) {C_UDMI(c,t,0) = C_VOF_G(c,pt)[0];
C_UDMI(c,t,1) = C_VOF_G(c,pt)[1];}end_c_loop(c,t)}
Free_Storage_Vars(sd,SV_VOF_RG,SV_VOF_G,SV_NULL);} }

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