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Cindy Jones October 10, 2002 16:19

question of DPM model
Hi, everyone I have two questions on the DPM model. 1. If my volume friction is larger than 10%, let say about 40%, can I still use DPM model to get rough results. If not, which kind of model I should use. ( I need to know the partical distribution)

2. How can I know the grid resolution is collect for the DPM model. I have a simple case, with different size of grids. One has 20,000 grids, for this case, I got 2500 particles. The other has 50,000 grids, I got more than 5000 particles.

Many thanks

CFD Newbie October 10, 2002 16:52

Re: question of DPM model
If your volume fraction is greater than 10% you must use the granular model as DPM won't account for particle-particle interactions that are important.

For the other question, the grid resolution is immaterial.


CFD Newbie

Cindy Jones October 10, 2002 17:30

Re: question of DPM model
Thanks for your reply.

Could you tell me that why the grid resolution is not important? how can I tell my result is correct if I got different results by using differnt number of grids? And why I got differnt particle number? Sorry for so many question.

Many Thanks


CFD Newbie October 10, 2002 22:21

Re: question of DPM model
For the sake of the particles, resolution is not important but you must do the grid analysis until you obtain independence for the resolution of the flow equations.

Fluent releases a particle for every cell you have in the surface, so the more cells you have the more particles.

If you analyse impact of particles, look at the percentages instead of the absolute number.

The only way to know if your simulations are OK is by comparing them with quality experimental results.



Cindy Jones October 11, 2002 13:54

Re: question of DPM model
Thanks so much for your help.

Have a nice weekend


Laika October 17, 2002 03:46

Re: question of DPM model
some comments:

--with volume fraction of 40 % you should indeed not use DPM. Granular can be an option, but maybe the particles are not granular. What kind of particles do you have, Cindy? Droplets, powder, ...?

--CFD Newbie tells Fluent releases one particle per cell. That's indeed the case with a surface-injection (and more correctly: it's one particle per face), but there are numerous other possibilities. You can also create an injection-file and release as much particles as you want.

--The grid resolution needed for good results have indeed nothing to do with the dpm-model. If you don't have experience with modelling for your application, you should test several grids and compare the results.

good luck,

Laika, still orbiting

yawi October 24, 2002 23:51

Re: question of DPM model
where is Granular model?

Laika October 25, 2002 03:51

Re: question of DPM model
it's one of the options for Eulerian multiphase simulation.

Laika, still orbiting

revalin herdianto November 18, 2002 22:58

Re: question of DPM model
Hi Newbie, you said that fluent releases particles at every cell? Does not fluent release particles on the surface that you define (for instance, inlet surface?)

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