[Dawood Al-Mosuli]

Hello,
I am new with using UDF. I tried to write one to represent the drag equations in the attached file for 3 phase flow (1 liquid and 2 solid).

I tried to write one similar (below) to that provided in section 2.4.2 DEFINE_EXCHANGE_PROPERTY in UDF manual [UDF for customizing the default Syamlal drag law in Fluent] , but it doesn't work. It seems that I have a problem with defining inputs [I got error when defining the solid fraction Es].

/************************************************** *************
UDF for customizing the default Syamlal drag law in Fluent
************************************************** **************/

#include "udf.h"

#define pi 4.*atan(1.)
#define diam2 0.000163

DEFINE_EXCHANGE_PROPERTY(custom_drag,cell,mix_thre ad,s_col,f_col)
{
Thread *thread_l, *thread_s;
real x_vel_l, x_vel_s, y_vel_l, y_vel_s, abs_v, slip_x, slip_y,
rho_l, rho_s, mu_l, reyp, afac,
bfac, void_l, vfac, fdrgs, taup, k_g_s;

/* find the threads for the gas (primary) */
/* and solids (secondary phases) */

thread_l = THREAD_SUB_THREAD(mix_thread, s_col);/* gas phase */
thread_s = THREAD_SUB_THREAD(mix_thread, f_col);/* liquid phase*/

/* find phase velocities and properties*/

x_vel_l = C_U(cell, thread_l);
y_vel_l = C_V(cell, thread_l);

x_vel_s = C_U(cell, thread_s);
y_vel_s = C_V(cell, thread_s);

slip_x = x_vel_l - x_vel_s;
slip_y = y_vel_l - y_vel_s;

rho_l = C_R(cell, thread_l);
rho_s = C_R(cell, thread_s);

mu_l = C_MU_L(cell, thread_l);
void_l = C_VOF(cell, thread_l);/* gas vol frac*/


k_g_s =(6 / 27) * (3.6*Es / pow(El,2.0) + pow (El,2.0)) + (0.11 + ( 2*K /(3 * pow(Vs, 2.0))));


return k_g_s;
}



I got the error : Es: undeclared variable
Can any one give me instructions about my mistakes and how to write a correct one.

[`e`]

You should have posted your UDF question in Fluent UDF and Scheme Programming. There are no attached files in your post.

Originally Posted by Dawood Al-Mosuli

I got the error : Es: undeclared variable
Can any one give me instructions about my mistakes and how to write a correct one.

If you have not declared "Es" then this variable is an undeclared variable and you should first declare this variable before attempting to access this variable.