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|ID||Project||Category||View Status||Date Submitted||Last Update|
|0003464||OpenFOAM||Bug||public||2020-03-04 00:35||2020-03-06 08:59|
|Fixed in Version|
|Summary||0003464: Unstable packing model in MPPICFoam without the isotropy model|
|Description||MPPICFoam shows very inaccurate results in Goldschmidt tutorial case with the isotropy model deactivated. It is even worse when there is no inlet flow in the simulation in which the max volume fraction was around 19 at the end. I will attach two videos that clearly show the issue. I don't know where the bug is but this is quite an issue as the isotropy model should be optional to MP-PIC. I have also tested a silo case (explicit) which diverged at about 0.8s and column tutorial case (implicit) which diverged at 0.28s.|
|Steps To Reproduce||Run $FOAM_TUTORIALS/lagrangian/MPPICFoam/Goldschmidt case without the isotropy model.|
|Additional Information||In the no-flow case, disabling the drag force affects the result drastically. Although it becomes better, it still remains unphysical. Damping model was off in all cases.|
|Tags||No tags attached.|
goldschmidt.mp4 (1,641,906 bytes)
goldschmidt_noFlow.mp4 (1,860,351 bytes)
||Do you see this with version 7? The cyclone tutorial has stopped working since version 7, and I don't know why. Might these be related?|
Oh, yes. There's a bug in dev. Look at the difference in the column case.
column.png (54,752 bytes)
column.png (54,752 bytes)
||Yes there is a considerable difference. I see this with version 7 as well. This packing behaviour made me think that there is something to do with the averaging method but I am not sure though. It is hard to track this bug. For me, column case without the isotropy model hangs at about 0.28s and the same happens with cellPointWallModified interpolation for U.air. There happens to be overpacking which is not usual with the implicit method. On the other hand if the drag force is disabled, the simulation runs till the end but then there is excessive scattering. This should be irrelevant to the averaging method.|
The image I posted is the difference between 7 and dev. If you see your problem in 7, too, then that is a
MPPIC has stability issues. Mostly this is when the parcels are too large relative to the cells, meaning a reliable average cannot be computed. There are other issues, too, though. When we wrote this, doing MPPIC reliably on polyhedral meshes wasn't a solved problem, and the only references we had when we first did the implementation were structured-mesh codes (Barracuda and Mfix) in which stability was achieved by various staggering procedures only possible on structured meshes. That situation may have changed now, I don't know.
There has been zero funding for improvement or extension of MPPIC since it's first release in 2013. If the basic limitations of our implementation of MPPIC is the issue here, then that will require someone to pay for additional research and development work to resolve it.
I'll find the bug that is causing the difference between 7 and dev. That's clearly a bug that has been introduced since version 7, and we have funding available (https://openfoam.org/maintenance) to do maintenance work of this sort.
Removing drag and isotropy will cause more scattering. Both act to reduce relative velocities within the system. Both will, in all likelihood, be necessary to get a physical solution. Damping, too, is important, as it is the only mechanism by which the sub-grid collision modelling dissipates energy. However, it can interact badly with the packing models. Again, limitations that we have never had the opportunity to fix.
||Thank you for the clarification and detailed explanation. I understand that the other issue is clearly a matter of funding. I just think that OpenFOAM is a great platform for MP-PIC too and could be quite unique with further developments which obviously require funding. I wish the big players in this field would be interested in it. Thanks in advance for your effort to find the bug that causes the difference between version 7 and dev.|
|2020-03-04 00:35||dscian||New Issue|
|2020-03-04 00:35||dscian||File Added: goldschmidt.mp4|
|2020-03-04 00:36||dscian||File Added: goldschmidt_noFlow.mp4|
|2020-03-04 16:13||will||Note Added: 0011228|
|2020-03-04 16:18||will||File Added: column.png|
|2020-03-04 16:18||will||Note Added: 0011229|
|2020-03-04 21:02||dscian||Note Added: 0011231|
|2020-03-05 08:47||will||Note Added: 0011232|
|2020-03-06 08:59||dscian||Note Added: 0011234|