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Kushagra April 11, 2008 15:15

Lagrangian Particle Tracking model In CFX
 
I am facing big times problem with the Lagrangian particle tracking model in CFX. I simulated flow in a hydrocyclone and once I obtained quite good flow field, I started tracking the particles with all the applicable forces applied (Turbulent dispersion force, pressure gradient force, gravity, byouancy) BUT I get wrong results all the time.

Could some one comment his experiences with Lagrangian model and accuracy of it in CFX-11? I have heard from other people as well that they have been facing the same problem as that of mine.

Please help. Thanks very much.

Regards, Kushagra

rvallejo September 19, 2009 11:57

Im facing the same problem. Could anyone help us ?

Thanks

John September 19, 2009 19:16

Quote:

Originally Posted by Kushagra
;87439
I am facing big times problem with the Lagrangian particle tracking model in CFX. I simulated flow in a hydrocyclone and once I obtained quite good flow field, I started tracking the particles with all the applicable forces applied (Turbulent dispersion force, pressure gradient force, gravity, byouancy) BUT I get wrong results all the time.

Could some one comment his experiences with Lagrangian model and accuracy of it in CFX-11? I have heard from other people as well that they have been facing the same problem as that of mine.

Please help. Thanks very much.

Regards, Kushagra

Can you provide details what's wrong with your results?

rvallejo September 22, 2009 12:57

Lagragian model provides a result where all the particles go to the underflow. I 'm using turbulent dispersion and Schiller Naumann drag force. I've tried virtual mass force and pressure gradiente force in addition, but they didn't work as well.

I'm using ANSYS CFX 11.01.

Best Regards,
Vallejo

rvallejo September 26, 2009 18:20

Quote:

Originally Posted by John (Post 229924)
Can you provide details what's wrong with your results?

Lagragian model provides a result where all the particles go to the underflow. I 'm using turbulent dispersion and Schiller Naumann drag force. I've tried virtual mass force and pressure gradiente force in addition, but they didn't work as well.

I'm using ANSYS CFX 11.01.

Best Regards,
Vallejo

leeportnoff March 12, 2010 19:26

When the particle diameters become small (less than 10 microns in air) the fluid can no longer be considered continuous. The drag coefficient on each particle, which is calculated using standard correlations (Schiller Neauman), must be divided by the Cunningham correction factor. The correction factor is greater than 1 which means that the effective particle drag coefficient goes down.
The cunningham correction factor is not used in CFX but if you use the "Particle Transport Drag Coefficient" in the Momentum Transfer tab in Pre you can specify any drag model that you need using CEL relations. First try to redo the Schiller Nauman relation, verify it with the CFX implementation and then correct it with the Cunningham factor. The Schiller Nauman will be the hardest part because it is an implicit relation.

gravis May 12, 2010 04:50

Quote:

Originally Posted by leeportnoff (Post 249760)
When the particle diameters become small (less than 10 microns in air) the fluid can no longer be considered continuous. The drag coefficient on each particle, which is calculated using standard correlations (Schiller Neauman), must be divided by the Cunningham correction factor. The correction factor is greater than 1 which means that the effective particle drag coefficient goes down.
The cunningham correction factor is not used in CFX but if you use the "Particle Transport Drag Coefficient" in the Momentum Transfer tab in Pre you can specify any drag model that you need using CEL relations. First try to redo the Schiller Nauman relation, verify it with the CFX implementation and then correct it with the Cunningham factor. The Schiller Nauman will be the hardest part because it is an implicit relation.

Does anyone have experience carrying out this implementation in CFX?

sei2006 May 12, 2010 05:41

check your turbulence model firstly.

leeportnoff December 2, 2010 22:18

LEVEL OF DIFFICULTY: ADVANCED
To get this working, I had to write a custom FORTRAN routine based on the pt_mom_source.F file included in ANSYS.
I compiled a custom pt_mom_custom.dll,
Expressions, functions, and variables > user routines > insert user routine and call 'drag'
option: particle user routine
calling name: pt_mom_custom
library name: pt_mom_custom
library path: <path to winnt> containing pt_mom_custom.dll

Then insert User Function
user routine name: drag
argument units: []
results units: []

Now, in your domain, under the 'Fluid pair models'
for 'drag force' select 'none'
check 'particle user source'
you should see your 'drag' routine for particle user routine

Lastly choose arguments and return variables.
** important ** the order you select these variables must match the order in your pt_mom_custom.h routine. i.e. It is by order of appearance, that cfx knows input DIAM_PT means particle.Mean Particle Diameter.


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