[CFDuser1995]

Dear all,


I am working on a project in which I would like to vary the porosity or viscous resistance in a domain over time. This is the UDF I tried to interpreted in Fluent:


#include "udf.h" //file that contains definitions for define functions and fluent operations

DEFINE_PROFILE(vis_res,th,i)
{
real x[ND_ND];
real a;
real t = CURRENT_TIME;
cell_t c;

begin_c_loop(c,th)
{
C_CENTROID(x,c,th);
if(t >= 0 && t <= 0.4)
a = 1e9;
else(t > 0.4 && t <= 0.8)
a = 1.0;
F_PROFILE(c,th,i) = a;
}
end_c_loop(c,th)
}


I received errors, I hope someone can help me to modify the UDF.



Thanks in advance!!

[AlexanderZ]

what kind of error did you get? describe in details, put here console output

best regards

[pakk]

Your "else" should be "else if".

[sshivam]

Hello, I am working on the same problem but in my case, I need to modify the visc resistance using an equation which is the function of wetting time of cell and total flow time. To do so, I am using the VOF approach to model the two-phase flow in porous media. So the following things I expect from UDF

1. Consider for a cell, it should record the time when the volume fraction becomes unity (tw) which varies for different cells.
2. The viscous resistance for secondary phase should be modified using the following equation a = (1/(3.7E-15*(current_time-tw)^2-1.75E-12*(current_time-tw)+6E-10))

any suggestions on this?

[pakk]

I guess the challenge is in the first part. In pseudo-code:

Add one UDM, which will represent the wetting time per cell. 
Initialize this UDM at a large value.
Add a scalar update:
 For each cell:
  Check if the vof is 1
  If so, check if the current time is below the UDM value. 
  If so, update the UDM value to the current time.

[sshivam]

#include "udf.h"

DEFINE_PROFILE(vis_res,c,i)
{
int phase_domain_index;
cell_t cell;
Thread *cell_thread;
Domain *subdomain;
real xc[ND_ND];

real current_time;
current_time = CURRENT_TIME;


sub_domain_loop(subdomain, mixture_domain, phase_domain_index) /* loop over all subdomains (phases) in the superdomain (mixture) */
{
if (DOMAIN_ID(subdomain) == 2) /* loop if secondary phase */

thread_loop_c (cell_thread,subdomain) /* loop over all cell threads in the secondary phase domain */
{

begin_c_loop_all (cell,cell_thread) /* loop over all cells in secondary phase cell threads */
{

C_CENTROID(xc,cell,cell_thread);

if

C_VOF(cell,cell_thread) = 1.; /* if volume fraction to 1*/

tw = C_time(c,t); /*wetting time*/

C_UDMI(c,t,0)=tw; /*saving wetting time*/

a = (1/(3.7E-15*(current_time-tw)^2-1.75E-12*(current_time-tw)+6E-10));

else

a =(1/9E-10);

F_PROFILE(c,t,i) = a;
}
}
}
end_c_loop_all (cell,cell_thread)

From ansys udf manual I have created this UDF. Since I am new to this. I would like to have your comments and suggestions on the same.

[pakk]

After some grammar fixes:

#include "udf.h"

DEFINE_PROFILE(vis_res,t,i)
{
int phase_domain_index;
cell_t cell;
Thread *cell_thread;
Domain *subdomain;
real a;
real current_time = CURRENT_TIME;

sub_domain_loop(subdomain, mixture_domain, phase_domain_index) /* loop over all subdomains (phases) in the superdomain (mixture) */
{
 if (DOMAIN_ID(subdomain) == 2) /* loop if secondary phase */
 thread_loop_c (cell_thread,subdomain) /* loop over all cell threads in the secondary phase domain */
 {
  begin_c_loop_all (cell,cell_thread) /* loop over all cells in secondary phase cell threads */
  {
  if (C_VOF(cell,cell_thread) > 0.99999) /* if volume fraction is close enough to one*/
   {
   if (C_UDMI(cell,t,0)==0) C_UDMI(cell,t,0)=current_time; /*saving wetting time only if it is the first time that it wets*/
   a = (1/(3.7E-15*pow(current_time-C_UDMI(cell,t,0),2)-1.75E-12*(current_time-C_UDMI(cell,t,0))+6E-10));
   } else {
   a = (1/9E-10);
   }
  F_PROFILE(cell,t,i) = a;
  }
 }
}
end_c_loop_all (cell,cell_thread)
}

Surely this will still fail, but at least it is closer.
And I think it can be simplified a lot further, but I am not so experienced with writing for secondary phases, and I don't have Fluent right now:

#include "udf.h"

DEFINE_PROFILE(vis_res,t,i)
{
cell_t cell;
real current_time = CURRENT_TIME;

begin_c_loop_all (cell,t) /* loop over all cells in secondary phase cell threads */
{
if (C_VOF(cell,t) > 0.99999) /* if volume fraction is close enough to one*/
 {
 if (C_UDMI(cell,t,0)==0) C_UDMI(cell,t,0)=current_time; /*saving wetting time only if it is the first time that it wets*/
 F_PROFILE(cell,t,i) = (1/(3.7E-15*pow(current_time-C_UDMI(cell,t,0),2)-1.75E-12*(current_time-C_UDMI(cell,t,0))+6E-10));
 } else {
 F_PROFILE(cell,t,i) = (1/9E-10);
 }
}
end_c_loop_all (cell,t)
}

Look at my changes critically, I did not test them.

[sshivam]

Thanks a lot for simplifications. I look forward to testing it