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-   -   Changing the acceleration of DPM particles?? (http://www.cfd-online.com/Forums/fluent-udf/75438-changing-acceleration-dpm-particles.html)

Wikie April 26, 2010 04:50

Changing the acceleration of DPM particles??
 
Hello,

I want to change just the acceleration for the DPM particles. Instead of -9.81 m/sē i want to have -0.004 m/sē. For all the other phases except the particles it should still be -9.81 m/sē. I tried to change it, including a UDF for the particles, but I'm new to FLUENT, especially to UDF and so it's not working in the way I want. In my case I can neglect all other acceleration, body forces an and drag forces.
This is my first try of the UFD. Can anybody help me with this problem??


#include "udf.h"

DEFINE_DPM_BODY_FORCE(particle_body_force,p,i)
{
real bforce=0;

if(i==1) bforce=-0.004;

/* an acceleration should be returned */
return (bforce);
}


Thanks a lot

Wikie

coglione April 27, 2010 02:47

Hello Wikie,

I'm not sure but I guess your particles still "feel" the gravitational acceleration of -9.81 m/s2 incorporated as standard body force term in the equation of motion for particles as soon as gravitation is on (operating condition). In my opinion to force a net-acceleration of -0.004 m/s2 your udf should return an acceleration of +9.806 m/s2.
Just try and see if this matches your expectations.

cheers

Wikie April 27, 2010 04:41

Hello coglione,

thanks for your reply. I tried your suggestion and changed the acceleration to +9.806 m/sē, but without any success. Based on an acceleration of -0.004m/sē the particle resistance time should be something about 20s, now it's just 0.41s. If I change the gravity for the whole setup to -0.004 m/sē it's working fine for the particles but not for the surrounding humid air flow.
In my opinion the main problem is how I'm trying to write the UDF. This is my first time programming an UDF. Could anybody please have a look at my first try?? As written above I want to have an acceleration for all particles everywhere and every time of -0.004 m/sē.


#include "udf.h"

DEFINE_DPM_BODY_FORCE(particle_body_force,p,i)
{
real bforce=0;

if(i==1) bforce=-0.004;

/* an acceleration should be returned */
return (bforce);
}


Thanks a lot
Wikie


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