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-   -   coupled DPM (http://www.cfd-online.com/Forums/fluent/28646-coupled-dpm.html)

Peter Kolb June 27, 2001 13:12

coupled DPM
 
I want to simulate the two-phase flow with coupled DPM. At the moment I have some problems with convergence resp. residual plot (especially the continuity) is fluctuant. Can anybody tell me if the fluctuations are normal and when convergence is reached? Or does anybody have an small example/tutorial where I can see how an optimal two-phase flow with coupled DPM is looking like.

Yours sincerely

Peter

Lanre June 27, 2001 14:42

Re: coupled DPM
 
The residuals will "jump" or "fluctuate" if the mass/momentum/energy source released by the DPM phase into the continuous phase is relatively large during coupled DPM calcs. This is expected. What you want is for the trend to decrease after a large number of iterations. To improve convergence, try:

1. increase number of DPM calcs per continuous phase iterations from default 10 to 40 (max recommended)

2. spatially distribute your injection. If you are injecting a large mass/momentum/heat source into a single cell, you may experience convergence difficulties. Use surface or group injection.

3. if turbulent, increase the number of "tries" or stochastic attempts. Since FLUENT divides the mass flow by the number of tries, this is the recommended approach when modelling combusting (heat/mass transfer) using the DPM model.

4. If this is a buoyancy-driven problem with the DPM bubbles being the source of momentum, consider patching initial values of upward velocity in the approximate volume where you anticipate the bubble plume to be.

Livo June 28, 2001 03:06

Re: coupled DPM
 
Lanre

1. increase number of DPM calcs per continuous phase iterations from default 10 to 40 (max recommended)

I am assuming it is increase number of continuous phase iterations per DPM iteration. Could you explain why this value must be increased. In the Fluent manual they just say this value depends upon the physics of the problem which has no meaning for me.

Thanks

Lanre June 28, 2001 09:58

Re: coupled DPM
 
Since the DPM model is applied in the Lagrangian sense, the continuous phase flow field must first be solved. The number of continuous phase iterations performed before a DPM injection needs adjusting depending on the sensitivity (strength on mass, momentum and energy sources) of the DPM trajectories on the continuous phase. In short, the more contiuous phase iterations between each DPM calc will lead to a more stable solution. The flip side is that if the DPM injections drive the flow, convergence will take a little longer. This is why I did not suggest >40 continuous phase calcs between each DPM injection.

hassansalem October 2, 2012 11:27

the no. of contiuous phase iterations between each DPM iterations depends on the amount of coupling between discrete and continuous phase...if this no.<3..this means there is strong coupling for example...so this no. depends strongly on the problem physics...

RodriguezFatz October 4, 2012 10:27

Quote:

Originally Posted by hassansalem (Post 384558)
the no. of contiuous phase iterations between each DPM iterations depends on the amount of coupling between discrete and continuous phase...if this no.<3..this means there is strong coupling for example...so this no. depends strongly on the problem physics...

Finally, over ten years after its creation, the problem can be officially declared as solved. Thank you so much grand master of DPM, now Peter Kolb can arise from standby and continue working.


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