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problem regarding droplet diameter udf

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Old   April 23, 2018, 13:26
Default problem regarding droplet diameter udf
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Chaitanya
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Dear members,
I am performing flow boiling simulations. In order to give secondary phase diameter, I have written the UDF for droplet diameter calculation. But, I am getting divergence after the first iteration only.

This is my udf...

#include "udf.h"

DEFINE_PROPERTY(droplet_dia,c,t)
{

Thread *thread_p, *thread_s;

real rho_p, rho_s, x_vel_p, y_vel_p, x_vel_s, y_vel_s, abs_u_p, abs_u_s, mu_p, mu_s, rey_p, rey_s, dd, sig;

Thread *tm = THREAD_SUPER_THREAD(t);
Thread *p = THREAD_SUB_THREAD(tm, 0);
Thread *s = THREAD_SUB_THREAD(tm, 1);

x_vel_p = C_U(c, p);
y_vel_p = C_U(c, p);
x_vel_s = C_U(c, s);
y_vel_s = C_U(c, s);
rho_p = C_R(c, p);
rho_s = C_R(c, s);
mu_p = C_MU_L(c, p);
mu_s = C_MU_L(c, s);

abs_u_p = sqrt(x_vel_p*x_vel_p + y_vel_p*y_vel_p);
abs_u_s = sqrt(x_vel_s*x_vel_s + y_vel_s*y_vel_s);

rey_p = (0.0126*abs_u_p*rho_p)/mu_p;
rey_s = (0.0126*abs_u_s*rho_s)/mu_s;
sig = 0.00327;

dd = 0.28*(sig/(rho_p*pow(abs_u_p,2)))*(pow(rey_s,(-1/6)))*(pow(rey_p,(2/3)))*(pow((rho_p/rho_s),(-1/3)))*(pow((mu_p/mu_s),(2/3)));

return dd;

}

So, possible suggestions that will use to solve the problem are highly appreciated
Thanking you
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Old   April 30, 2018, 14:01
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Micael
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two things pop up to me at first glance:
- for y velocity component, you probably want C_Y instead of C_U macro.
- you have some integer divisions, like 2/3. Those won't return what you might expect. Have a look into C programming regarding that topic. For instance, in C, 2/3 returns 0. However, 2./3 returns 0.6666 (actually will returns more digit than that).
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Old   May 8, 2018, 10:58
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tahir
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Quote:
Originally Posted by Micael View Post
two things pop up to me at first glance:
- for y velocity component, you probably want C_Y instead of C_U macro.
- you have some integer divisions, like 2/3. Those won't return what you might expect. Have a look into C programming regarding that topic. For instance, in C, 2/3 returns 0. However, 2./3 returns 0.6666 (actually will returns more digit than that).
Hi
Did you find the answer. I am also doing the twophase simulation in fluent and also need help.
Can we communicate on skype
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