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Old   June 5, 2007, 05:24
Default Drag force correction
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Hello !

Does anybody knows how can I use the Epstein drag force instead of Stokes-Cunningham on FLUENT? I'm trying to simulate a multiphase flow of a gas at low pressure with a low volume fraction of nanoparticles, in which the nanoparticle's size is much smaller than the mean free path of the gas molecules.

Thanks in advance
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Old   June 5, 2007, 09:07
Default Re: Drag force correction
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You can write something like this for your UDF and use it in the interaction panel for multiphase model. It seems you talking about dpm model. If so I don't have a sample for that. Hope this helps.

#include "udf.h"

#include "sg_mphase.h"

#define diam2 3.e-6

DEFINE_EXCHANGE_PROPERTY(custom_drag, cell, mix_thread, s_col, f_col)


Thread *thread_g, *thread_s;

real x_vel_g, x_vel_s, y_vel_g, y_vel_s, z_vel_g, z_vel_s,

rho_g, rho_s, mu_g, void_g, k_g_s, eps_s;

thread_g = THREAD_SUB_THREAD(mix_thread, s_col);/*gas phase*/

thread_s = THREAD_SUB_THREAD(mix_thread, f_col);/* solid phase*/

x_vel_g = C_U(cell, thread_g);

y_vel_g = C_V(cell, thread_g);

z_vel_g = C_W(cell, thread_g);

x_vel_s = C_U(cell, thread_s);

y_vel_s = C_V(cell, thread_s);

z_vel_s = C_W(cell, thread_s);

rho_g = C_R(cell, thread_g);

rho_s = C_R(cell, thread_s);

void_g = C_VOF(cell, thread_g);/* gas vol frac*/

eps_s = C_VOF(cell, thread_s);/* solid vol frac*/

mu_g = C_MU_L(cell, thread_g);

k_g_s = .... ;

return k_g_s;

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Old   June 5, 2007, 10:11
Default Re: Drag force correction
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For the DPM model, write a UDF using the DEFINE_DPM_DRAG-macro. Example code is available in the manual. You then choose to use your UDF instead of Stokes-Cunningham in the drop-down menu in the DPM panel.

Good luck!

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Old   June 6, 2007, 00:09
Default Re: Drag force correction
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Thank you both for readily responses ! I will try something with UDF, though UDF seems tough work for a newbie like me. I will check the manual, and more suggestions are welcomed too.

Thanks everyone for your kind help !!!
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