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-   -   steady or unsteady? (in dpm) (http://www.cfd-online.com/Forums/fluent/31360-steady-unsteady-dpm.html)

 winnie April 28, 2003 04:49

steady or unsteady? (in dpm)

Hi, everyone

I would like to discuss the steady and unsteady particle Lagrangian discrete phase model with you.

In Fluent document, we can find the explaination of steady and unsteady model as follows:

The steady-particle Lagrangian discrete phase model is suited for flows in which particle streams are injected into a continuous phase flow with a well-defined entrance and exit condition.

The unsteady-particle discrete phase model, however, is capable of modeling continuous suspensions of particles.

In my opinion, whether we should use steady or unsteady model depends on the procedure of each model:

1) steady model: In each iteration, firstly the continuous phase flow field is solved and then based on it the particle streams with definite entrance and exit condition are created. Iteration goes on until both the continuous phase flow field and particle trajectory never change.

2)unsteady model: particle trajectory is calculated step by step; another word, after each time step, particle will be advanced to a new position. In each time step, the iteration between continuous phase and particle is going on. In each iteration, there are sub-iteration in the continuous phase per DPM iteration which is controled by the "number of continuous phase iteration per DPM iteration" in Discrete Phase Model panel.

From what I have discussed above, I find that a problem such as bubbly flow in a pipe can be solved by using both steady and unsteady model and the result of a steady one should be the same as the result of an unsteady one when the particle of the unsteady model has escaped from the exit.

I don't know if my understanding is right. Hope anyone who has experience in DPM can give me some suggestions.

Thank you very much for reading a so long message.

Regards

winnie

 phd_y2k2001 April 28, 2003 12:30

Re: steady or unsteady? (in dpm)

In the real life, there are few steady state particle flow.

Most unsteady cases become virtually steady if we can remove the same amount of particles from the domain by any means. Accumulation of particles in the domain will make the local density of the particles more than 10% and the DPM will no longer will be applicable.

Well, in case I am confusing you, I will stop here :)

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