mass source term to boundary cells adjacent to a wall

Kimia · June 4, 2017, 20:39

Hi all,

I am trying to write a UDF code for applying mass source term only to those cells adjacent to a wall boundary. The idea is to model evaporation by considering a static interface between water and vapor and applying convective heat transfer and mass source term to it.
I have defined the interface as a wall and written the code below to assign proper mass source terms to those cells adjacent to it. I am sure the code is not right. I will be beyond grateful if you could help me to write it properly.
Thank you so much.

#include "udf.h"

//get the boundary cells
DEFINE_ON_DEMAND(on_demand_calc)
{
Domain *d;
face_t f;
cell_t c;
Thread *t;
real source;

d= Get_Domain(1);
Thread *tb = Lookup_Thread(d,1); //Get boundary thread, wall zone ID is 1
// which is assumed to be the liquid-vapor interface
thread_loop_c(t,d)
{
begin_c_loop(c,t)
{

if (c == F_C0(f,tb)) //i.e if cell is adjacent to the wall boundary
{

source= 100;
C_UDMI(c,t,0)=source;
}
else
{
source=0;
C_UDMI(c,t,0)=source;
}

}
end_c_loop(c,t)
}

}

//define the source term
DEFINE_SOURCE(mass_source, c, t, dS, eqn)
{
//Thread *t;
//cell_t c;

real mdot;
mdot=C_UDMI(c,t,0);

return (mdot);
}

KaLium · June 5, 2017, 02:50

Is that a correct way to use F_C0 ?

KaLium · June 5, 2017, 03:07

Maybe you could use a face-loop:

thread = Lookup_Thread(domain,P_ID);
begin_f_loop(f,thread)
{
c0 = F_C0(f,thread);
t0 = THREAD_T0(thread);
source= 100.0;
C_UDMI(c0,t0,0)=source;
end_f_loop(f,thread)
}

Kimia · June 5, 2017, 04:57

Thank you so much for your help. I tried with face loop and it seems that it works!
I really appreciate your help.

vidyadhar · November 1, 2018, 08:02

Hello Kimia!

I am also trying to write UDF for modeling evaporation (copied below and also attached herewith).
My problem involves evaporation of a liquid into its vapor.

I have few queries:
1. Whether this way of writing UDF is okay? or can you help me in writing UDF for simulating evaporation.

2. Whether source terms for evaporation mass flux are to be applied over the entire liquid and vapor regions? or in a particular cells near the interface?
How to apply the source terms at a particular region?
3. How to get the calculated mass fluxes in Fluent GUI? whether UDF will create a field for the evaporative mass flux in Fluent?

Thanks in advance!

#include "udf.h"
#include "sg_mphase.h"
#define T_SAT 343
#define LAT_HT 2455.1345e3
#define CON 20
DEFINE_SOURCE(vap_src, cell, pri_th, dS, eqn)
{
Thread *mix_th, *sec_th;
real m_dot_v;
real v_s;
mix_th = THREAD_SUPER_THREAD(pri_th);
sec_th = THREAD_SUB_THREAD(mix_th, 1);
/*m_dot_v=0.;*/
if (NULL != THREAD_STORAGE(mix_th,SV_VOF_G))
{
v_s = C_VOF_G(cell,mix_th)[0];
}
if(C_T(cell,mix_th)>=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot_v = CON*(C_T(cell,mix_th)-T_SAT)*fabs(v_s);

dS[eqn] = 0.;
}
}

if(C_T(cell,mix_th)<=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot_v = -CON*(T_SAT-C_T(cell,mix_th))*fabs(v_s);
dS[eqn] = 0.;
}
}
return m_dot_v ;
}

DEFINE_SOURCE(liq_src, cell, sec_th, dS, eqn)
{
Thread *mix_th, *pri_th;
real m_dot_l;
real v_s;
mix_th = THREAD_SUPER_THREAD(sec_th);
pri_th = THREAD_SUB_THREAD(mix_th, 0);
/*m_dot_l=0.;*/
if (NULL != THREAD_STORAGE(mix_th,SV_VOF_G))
{
v_s = C_VOF_G(cell,mix_th)[0];
}
if(C_T(cell,mix_th)>=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot_l = -CON*(C_T(cell,mix_th)-T_SAT)*fabs(v_s);
dS[eqn] = 0.;
}
}
if(C_T(cell,mix_th)<=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot_l = CON*(T_SAT-C_T(cell,mix_th))*fabs(v_s);
dS[eqn] =0.;
}
}

return m_dot_l;
}

DEFINE_SOURCE(enrg_src, cell, mix_th, dS, eqn)
{
Thread *pri_th, *sec_th;
real m_dot;
real v_s;
pri_th = THREAD_SUB_THREAD(mix_th, 0);
sec_th = THREAD_SUB_THREAD(mix_th, 1);
if (NULL != THREAD_STORAGE(mix_th,SV_VOF_G))
{
v_s = C_VOF_G(cell,mix_th)[0];
}
if(C_T(cell,mix_th)>=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot = -CON*(C_T(cell,mix_th)-T_SAT)*fabs(v_s);
dS[eqn] = -CON*fabs(v_s);
}
}

if(C_T(cell,mix_th)<=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot = CON*(T_SAT-C_T(cell,mix_th))*fabs(v_s);
dS[eqn] = CON*fabs(v_s);
}
}
return LAT_HT*m_dot; }

vidyadhar · November 5, 2018, 06:49

Quote:

Originally Posted by Kimia

Hi all,

I am trying to write a UDF code for applying mass source term only to those cells adjacent to a wall boundary. The idea is to model evaporation by considering a static interface between water and vapor and applying convective heat transfer and mass source term to it.
I have defined the interface as a wall and written the code below to assign proper mass source terms to those cells adjacent to it. I am sure the code is not right. I will be beyond grateful if you could help me to write it properly.
Thank you so much.

#include "udf.h"

//get the boundary cells
DEFINE_ON_DEMAND(on_demand_calc)
{
Domain *d;
face_t f;
cell_t c;
Thread *t;
real source;

d= Get_Domain(1);
Thread *tb = Lookup_Thread(d,1); //Get boundary thread, wall zone ID is 1
// which is assumed to be the liquid-vapor interface
thread_loop_c(t,d)
{
begin_c_loop(c,t)
{

if (c == F_C0(f,tb)) //i.e if cell is adjacent to the wall boundary
{

source= 100;
C_UDMI(c,t,0)=source;
}
else
{
source=0;
C_UDMI(c,t,0)=source;
}

}
end_c_loop(c,t)
}

}

//define the source term
DEFINE_SOURCE(mass_source, c, t, dS, eqn)
{
//Thread *t;
//cell_t c;

real mdot;
mdot=C_UDMI(c,t,0);

return (mdot);
}

Hi Kimia,

Could you get success in executing the evaporation UDF.
In the UDF that you have written in this post:
You are storing source in User defined memory under DEFINE_ON_DEMAND. Then you are using UDMI(c0,t0,0) in DEFINE_SOURCE.

Since DEFINE_ON_DEMAND executes only once, if the source term is a function of temperature, how to change the UDF so that in each iteration the mdot term will be updated? (As in your case, you have used source term=100 which is a constant)

Albert Lee · May 2, 2019, 02:47

Quote:

Originally Posted by vidyadhar

Hello Kimia!

I am also trying to write UDF for modeling evaporation (copied below and also attached herewith).
My problem involves evaporation of a liquid into its vapor.

I have few queries:
1. Whether this way of writing UDF is okay? or can you help me in writing UDF for simulating evaporation.

2. Whether source terms for evaporation mass flux are to be applied over the entire liquid and vapor regions? or in a particular cells near the interface?
How to apply the source terms at a particular region?
3. How to get the calculated mass fluxes in Fluent GUI? whether UDF will create a field for the evaporative mass flux in Fluent?

Thanks in advance!

#include "udf.h"
#include "sg_mphase.h"
#define T_SAT 343
#define LAT_HT 2455.1345e3
#define CON 20
DEFINE_SOURCE(vap_src, cell, pri_th, dS, eqn)
{
Thread *mix_th, *sec_th;
real m_dot_v;
real v_s;
mix_th = THREAD_SUPER_THREAD(pri_th);
sec_th = THREAD_SUB_THREAD(mix_th, 1);
/*m_dot_v=0.;*/
if (NULL != THREAD_STORAGE(mix_th,SV_VOF_G))
{
v_s = C_VOF_G(cell,mix_th)[0];
}
if(C_T(cell,mix_th)>=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot_v = CON*(C_T(cell,mix_th)-T_SAT)*fabs(v_s);

dS[eqn] = 0.;
}
}

if(C_T(cell,mix_th)<=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot_v = -CON*(T_SAT-C_T(cell,mix_th))*fabs(v_s);
dS[eqn] = 0.;
}
}
return m_dot_v ;
}

DEFINE_SOURCE(liq_src, cell, sec_th, dS, eqn)
{
Thread *mix_th, *pri_th;
real m_dot_l;
real v_s;
mix_th = THREAD_SUPER_THREAD(sec_th);
pri_th = THREAD_SUB_THREAD(mix_th, 0);
/*m_dot_l=0.;*/
if (NULL != THREAD_STORAGE(mix_th,SV_VOF_G))
{
v_s = C_VOF_G(cell,mix_th)[0];
}
if(C_T(cell,mix_th)>=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot_l = -CON*(C_T(cell,mix_th)-T_SAT)*fabs(v_s);
dS[eqn] = 0.;
}
}
if(C_T(cell,mix_th)<=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot_l = CON*(T_SAT-C_T(cell,mix_th))*fabs(v_s);
dS[eqn] =0.;
}
}

return m_dot_l;
}

DEFINE_SOURCE(enrg_src, cell, mix_th, dS, eqn)
{
Thread *pri_th, *sec_th;
real m_dot;
real v_s;
pri_th = THREAD_SUB_THREAD(mix_th, 0);
sec_th = THREAD_SUB_THREAD(mix_th, 1);
if (NULL != THREAD_STORAGE(mix_th,SV_VOF_G))
{
v_s = C_VOF_G(cell,mix_th)[0];
}
if(C_T(cell,mix_th)>=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot = -CON*(C_T(cell,mix_th)-T_SAT)*fabs(v_s);
dS[eqn] = -CON*fabs(v_s);
}
}

if(C_T(cell,mix_th)<=T_SAT)
{
if(0<C_VOF(cell,mix_th)<1)
{
m_dot = CON*(T_SAT-C_T(cell,mix_th))*fabs(v_s);
dS[eqn] = CON*fabs(v_s);
}
}
return LAT_HT*m_dot; }

Hi vidyadhar!
Have you solved this kind of simulation of evaporation and using VOF?
Recently, I also tried to simulation the evaporation in a tank, the udf of mass transfer are same as your post. When I simulated for some time, the temperature distribution in the tank is weird. It shows that the temperature of vapor phase reaches the maximum of temperature distribution (I loaded the heat source at the liquid side).
Have you confronted this kind of problem? If yes, how did you solved it ? Could you do me a favor? Thank you very much!
(The question I was posted on Using Fluent VOF and Lee model to simulate mass transfer of two phase)

kangluyang · November 15, 2020, 11:53

You can update the UDM using DEFINE_ADJUST in fluent during iteration.

June 4, 2017, 20:39	mass source term to boundary cells adjacent to a wall	#1
Kimia New Member Join Date: Jun 2016 Posts: 17 Rep Power: 10	Hi all, I am trying to write a UDF code for applying mass source term only to those cells adjacent to a wall boundary. The idea is to model evaporation by considering a static interface between water and vapor and applying convective heat transfer and mass source term to it. I have defined the interface as a wall and written the code below to assign proper mass source terms to those cells adjacent to it. I am sure the code is not right. I will be beyond grateful if you could help me to write it properly. Thank you so much. #include "udf.h" //get the boundary cells DEFINE_ON_DEMAND(on_demand_calc) { Domain d; face_t f; cell_t c; Thread t; real source; d= Get_Domain(1); Thread tb = Lookup_Thread(d,1); //Get boundary thread, wall zone ID is 1 // which is assumed to be the liquid-vapor interface thread_loop_c(t,d) { begin_c_loop(c,t) { if (c == F_C0(f,tb)) //i.e if cell is adjacent to the wall boundary { source= 100; C_UDMI(c,t,0)=source; } else { source=0; C_UDMI(c,t,0)=source; } } end_c_loop(c,t) } } //define the source term DEFINE_SOURCE(mass_source, c, t, dS, eqn) { //Thread t; //cell_t c; real mdot; mdot=C_UDMI(c,t,0); return (mdot); }

June 5, 2017, 03:07		#3
KaLium Senior Member Kal-El Join Date: Apr 2017 Location: Finland Posts: 150 Rep Power: 9	Maybe you could use a face-loop: thread = Lookup_Thread(domain,P_ID); begin_f_loop(f,thread) { c0 = F_C0(f,thread); t0 = THREAD_T0(thread); source= 100.0; C_UDMI(c0,t0,0)=source; end_f_loop(f,thread) } Kimia likes this.

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June 5, 2017, 02:50		#2
KaLium Senior Member Kal-El Join Date: Apr 2017 Location: Finland Posts: 150 Rep Power: 9	Is that a correct way to use F_C0 ?

June 5, 2017, 04:57		#4
Kimia New Member Join Date: Jun 2016 Posts: 17 Rep Power: 10	Thank you so much for your help. I tried with face loop and it seems that it works! I really appreciate your help.

November 15, 2020, 11:53		#8
kangluyang New Member LouisK Join Date: Aug 2013 Location: Shanghai,China Posts: 10 Rep Power: 13	You can update the UDM using DEFINE_ADJUST in fluent during iteration.