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Old   October 26, 2011, 14:19
Default Divergence detected in AMG solver: pressure correction
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andi
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Hi,
its a air flow simulation.
i have a porous cell zone.
the inlet speed is ~16m/s , diameter ~45mm and the turbulence intensity ~5% and a pressure outlet with 116mm diameter (hydraulic diameter) and ~5% turbulence. i have a mesh with ~500k cells. max skewness is under 0,80 and max. aspect ratio under 10. i have the standard k-epsilon-model active. solution options are default.
the error iam getting is : Divergence detected in AMG solver: pressure correction. i played with the under-relaxtion factor for pressure and decreased it. but it doenst help. i did the same simulation with a different mesh (only ~300k cells) and it worked after setting the limit for maximum absolute pressure to maximum (1e+20).
what can i do to get rid of that problem? any suggestions?
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Old   October 27, 2011, 03:32
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Kristian Etienne Einarsrud
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Hi,

I have also encountered this problem, although for bubbly flows, not porous materials. For my cases, the problem was solved by changing the pressure AMG-cycle from the default (in my case) C-cycle to a flexible cycle.

You can change these settings under Solution Controls -> Advanced
-> Multigrid

Maybe this can resolve your problems as well?

Cheers!
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Old   October 27, 2011, 05:40
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it doesnt help. thanks for the suggestion anyway!
I played a little with the "sweeps" under multigrid, it ran ok until ~700 Iterations.
Then again, "Divergence detected in AMG solver: pressure correction" error..

Last edited by thisisit; October 27, 2011 at 06:38.
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Old   October 28, 2011, 09:36
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andi
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sorry for double-post, but if u need any other information, that could help you to help me, just let me know!

ok, for now i may have solved my problem.
its my understanding, that especially in the first iterations the simulation was not stable and divergence was detected by the solver
for the first 30 iterations i activated the "laminar flow" option in the porous cell zone and then deactivated it again.
it seems that this helps in my case, because iam in iteration ~1500 and my simulation reaches convergence almost.. yep it worked.

Last edited by thisisit; October 29, 2011 at 05:05.
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Old   October 31, 2011, 05:13
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Kristian Etienne Einarsrud
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Good that it worked out!
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Old   February 6, 2013, 12:14
Default meshing quality or pressure corection
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michel
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Dear all,

I am trying to simulate micro-cylinders embedded in a rectangular microchannel so I simplified the model with a unit cell which is a square microchannel including a micro-cylinder with an inlet and outlet by apply periodic boundary condition in the inlet and outlet (I used mass-flow rate for inlet boundary condition).
The point is when I applied periodic boundary condition in Fluent, an error just appeared before the first iteration calculating solution "divergence detected in AMG solver-pressure correction" . Although I tried to overcome this problem by reducing under relaxation factor and change some parameters in solution control, unfortunately I could not be able to solve it.
In the other hand when I want to make periodic region in inlet and outlet in mesh utility, but the coordinate system light yellow prevent to well define it.

I suggest maybe it is related to mesh quality and i have to make a finer mesh, do you have any suggestion about the mesh or solving this problem.
Any help would be greatly appreciated.

Regards
Michel
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Old   September 24, 2013, 13:12
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Ravichandra Rangappa
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Quote:
Originally Posted by KristianEtienne View Post
Hi,

I have also encountered this problem, although for bubbly flows, not porous materials. For my cases, the problem was solved by changing the pressure AMG-cycle from the default (in my case) C-cycle to a flexible cycle.

You can change these settings under Solution Controls -> Advanced
-> Multigrid

Maybe this can resolve your problems as well?

Cheers!
Yes, It worked.
changing to multigrid is getting smooth flow during iteration, in my case default setting gets divergence bellow 100 iteration, now running more than 200 with out any spikes or back pressure, hope it will converge soon..........thanks
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Old   April 1, 2014, 06:54
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Kieran
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Running the simulation in the coupled solver seemed to help for me.
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