Angular Velocity of the particle

vagaikwa · June 28, 2013, 15:28

Hello,
I am using DPM model and trying to simulate flow of few particles through fluid. How do I know if my particles are having any angular velocity? And if not how can i impart angular velocity? I have enabled Saffman Lift but it is not generating any lift on my particles.

Thanks.
Varad.

sadjad.s · June 29, 2013, 06:52

Hi mate,
I am rather sure DPM can not see angular motion of particles.
You see, particles should be too small, hence angular velocity would be negligible.
About Saffman force, if particle and flow velocities become equal, which will be after a while, Saffman force is zero.

vagaikwa · June 29, 2013, 10:34

Thanks for your reply.
Yes that is what is exactly happening. The velocities of particle and fluid becomes equal after a while. So which model should I adopt if I want to simulate particulate flow and see the translational and angular velocity effects and lift on the particles too.

sadjad.s · June 29, 2013, 10:40

To see that you need to model 6DoF (Dynamic mesh). But problem is that it fails when particles strike to each other.

vagaikwa · June 29, 2013, 10:46

I thought of using Dynamic mesh. But the issue is my particle diameter size to tube diameter size is 0.04. Also I have to simulate flow 8 particles and then go upto 100-200 particles.

sadjad.s · June 29, 2013, 10:52

This is DPM limitation and you may have to neglect angular velocity.
Other problem is your rather big particles sizes. I mean particles with 4% size of characteristic length are rather big for Discrete Phase and can fully change flow pattern. You may switch to Eulerian method.

vagaikwa · June 29, 2013, 10:52

Sadjad,
Do u think I should still go for dynamic mesh?

vagaikwa · June 29, 2013, 10:56

Oh the size is big? I thought it is small. Because the references I am using they have the ratio of particle to tube diameter size higher than what I am trying to do. Thanks for your help brother.

ldm273507 · December 26, 2013, 03:09

Hi,friend. I want to simualte the movement of water droplet. If you konw how to control the velocity of the water droplet using the DPM model? I write an UDF about this, but it's incorrect, could you give me some suggestion?
#include "udf.h"
#include "dpm.h"
DEFINE_ADJUST(my_adjust,d)
{
Tracked_Particle *tp;
cell_t c=P_CELL(tp);
Thread *t=P_CELL_THREAD(tp);
Particle *p;
if(P_POS(p)[2]<14.8&&P_POS(p)[2]>=13.4)
begin_particle_cell_loop(p,c,t)
{
P_VEL(p)[2] = -0.2;
}
end_particle_cell_loop(p,c,t)
}
"Uninitialized varible ’tp' used" and "Uninitialized varible ’p' used" appears when I compile the UDF.
Thank you.

June 28, 2013, 15:28	Angular Velocity of the particle	#1
vagaikwa Member Join Date: Apr 2012 Posts: 48 Rep Power: 14	Hello, I am using DPM model and trying to simulate flow of few particles through fluid. How do I know if my particles are having any angular velocity? And if not how can i impart angular velocity? I have enabled Saffman Lift but it is not generating any lift on my particles. Thanks. Varad.

June 29, 2013, 06:52	Answer	#2
sadjad.s Member sadjad Join Date: Jan 2012 Posts: 72 Rep Power: 14	Hi mate, I am rather sure DPM can not see angular motion of particles. You see, particles should be too small, hence angular velocity would be negligible. About Saffman force, if particle and flow velocities become equal, which will be after a while, Saffman force is zero. __________________ ICEM, CFX and Fluent expert

June 29, 2013, 10:40	Answer	#4
sadjad.s Member sadjad Join Date: Jan 2012 Posts: 72 Rep Power: 14	To see that you need to model 6DoF (Dynamic mesh). But problem is that it fails when particles strike to each other. __________________ ICEM, CFX and Fluent expert

June 29, 2013, 10:52	Answer	#6
sadjad.s Member sadjad Join Date: Jan 2012 Posts: 72 Rep Power: 14	This is DPM limitation and you may have to neglect angular velocity. Other problem is your rather big particles sizes. I mean particles with 4% size of characteristic length are rather big for Discrete Phase and can fully change flow pattern. You may switch to Eulerian method. __________________ ICEM, CFX and Fluent expert

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June 29, 2013, 10:34		#3
vagaikwa Member Join Date: Apr 2012 Posts: 48 Rep Power: 14	Thanks for your reply. Yes that is what is exactly happening. The velocities of particle and fluid becomes equal after a while. So which model should I adopt if I want to simulate particulate flow and see the translational and angular velocity effects and lift on the particles too.

June 29, 2013, 10:46		#5
vagaikwa Member Join Date: Apr 2012 Posts: 48 Rep Power: 14	I thought of using Dynamic mesh. But the issue is my particle diameter size to tube diameter size is 0.04. Also I have to simulate flow 8 particles and then go upto 100-200 particles.

June 29, 2013, 10:56		#8
vagaikwa Member Join Date: Apr 2012 Posts: 48 Rep Power: 14	Oh the size is big? I thought it is small. Because the references I am using they have the ratio of particle to tube diameter size higher than what I am trying to do. Thanks for your help brother.

December 26, 2013, 03:09		#9
ldm273507 New Member Rodman Join Date: Dec 2013 Posts: 7 Rep Power: 13	Hi,friend. I want to simualte the movement of water droplet. If you konw how to control the velocity of the water droplet using the DPM model? I write an UDF about this, but it's incorrect, could you give me some suggestion? #include "udf.h" #include "dpm.h" DEFINE_ADJUST(my_adjust,d) { Tracked_Particle tp; cell_t c=P_CELL(tp); Thread t=P_CELL_THREAD(tp); Particle *p; if(P_POS(p)[2]<14.8&&P_POS(p)[2]>=13.4) begin_particle_cell_loop(p,c,t) { P_VEL(p)[2] = -0.2; } end_particle_cell_loop(p,c,t) } "Uninitialized varible ’tp' used" and "Uninitialized varible ’p' used" appears when I compile the UDF. Thank you.