[Achini]

Hello!

I am using the following UDF to model particle wall forces. The force is applied only on half of the particles and I'm expecting to see a portion of particles moving towards the wall.

I took the minimum distance between the particle and the wall via a loop over the boundary face and I have considered each direction separately.

But using the below UDF I couldn't see particle trajectories. Can you please help me figure out the reason for that?

It feels like the force is not being applied to particles.
I would be much grateful if you could help me fix this.


#include "udf.h"
#include "dpm.h"
#include "dpm_mem.h"
#include "surf.h"
#include "math.h"

int particleid;

DEFINE_DPM_BODY_FORCE(particle_body_force,p,i) /* Fluent macro to define particle body force*/
{
double force,dw,area,facearea,e,K;
real xw[ND_ND];

real vec[ND_ND];

Domain*d;
cell_t c;
Thread *t;
face_t f;



d = Get_Domain(1);

K = 4.00365*pow(10,(-24));


particleid = (int)p->part_id;

if (particleid % 2 == 0) return(0); /*This part makes it such that only half of the particles get the force. */

c = P_CELL(p); /*Get the cell and thread that the particle is currently in */

/* t = P_CELL_THREAD(p);*/

if (i==0) /* to consider the direction */
{
t = Lookup_Thread(d, 7); /* channel wall on yz plane */

force = 0; /* reset force*/

dw=500;
begin_f_loop(f, t)
{

F_CENTROID(xw,f,t); /* Center of the face*/


NV_VV(vec, =, xw, -, P_POS(p)); /* vector conecting the particlea nd the face center*/

if (dw>NV_MAG(vec))
{
dw = NV_MAG(vec);

}


end_f_loop(f, t)

}

force = (K/(vec[i]* vec[i]))-(K/((150-vec[i])*(150-vec[i]))); /* calculation of the net force by attractions from walls */
}

else if (i==1) /* to consier the direction */
{
t = Lookup_Thread(d, 8); /* channel wall on xy plane*/

force =0; /* reset force*/

dw=500;
begin_f_loop(f, t)
{

F_CENTROID(xw,f,t); /* Center of the face*/


NV_VV(vec, =, xw, -, P_POS(p)); /* vector conecting the particlea nd the face center*/
if (dw>NV_MAG(vec))
{
dw = NV_MAG(vec);
}

end_f_loop(f, t)

}

force = (K/(vec[i])* (vec[i]))-(K/((100-vec[i])*(100-vec[i]))); /* calculation of the net force by attractions from walls on yz plane*/

}

else
{
force=0;
}

return (force/P_MASS(p));


}


Thank you!

[pakk]

Show what you see instead... What does the TUI show when you release particles?

[Achini]

The particles flow straight through the channel without any disturbance. no change in particle trajectories.

[pakk]

In the first post, you said there were no trajectories. Did you change something?

[Achini]

Sorry, my mistake.

I was trying to say that there was no change in particle trajectories. I can see them but they are not diverting towards the wall due to the attraction force.

what could be the season for that?

Thank you!

[AlexanderZ]

write to file the values of force, you are applying to model

force/P_MASS(p)

check if it is enough to influence particle trajectories

[Achini]

Thank you AlexanderZ!

I will try it.

[Achini]

Hello!

This is a snap of particle tracks from my simulation.



In the particle trajectories, there's a high inclination in some points.
I was expecting a gradual diversion towards walls.

Please help!
Thanks

[pakk]

Picture did not upload...

[Achini]

Hello Pakk,

The image hadn't uploaded. Sorry about it.


https://www.dropbox.com/s/u0pgx46j4c...FFPT1.png?dl=0



This is how the particle trajectories appear. Hope it's visible now.

Although the force is exerted by all four walls, the trajectories have diverted only towards one face. Also, I can't understand the reason for the high inclination at some points.

I would be grateful if you could help me with this.
Thank you!

[pakk]

Particles will go to the closest wall. I have no idea where the walls are in your picture. According to the UDF, they are 100 m and 150 m apart from each other, the scale on your picture is 100 micrometer, so it looks like your particles are just very close to one of the walls.

[Achini]

Thank you Pakk for your reply.

The two black lines beside the tracks are the walls.

Even the particles close to one wall moves towards the other wall. That's the problem I have.
Also what might be the reason for the sudden change in the gradient of the particle trajectories.

Thank you!

[pakk]

In the UDF your walls are 150 m apart in the x-direction, and 100 m apart in the y-direction, and there are no walls in the z-direction. If you want your UDF to work with your geometry, your geometry should be the same.

I don't know which perspective your picture is showing, but the walls are 100 micrometer apart.

You are somehow off by a factor of at least 1000000. Fix that!
Possible, the orientation of your UDF is different from the orientation of your geometry. Fix that!

[angel_97]

Hello, i have the same problem, i don't feel any lateral force on the particle. Maybe can be a problem of loop when you find the minimum distance. It's not a correct value and you have a lot of oscillation.