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Too many iterations in pimplefoam and extreme Courant Number |
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December 21, 2020, 11:58 |
Too many iterations in pimplefoam and extreme Courant Number
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#1 | |||
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Hi, I'm running a simulation in OF8 about air running into two chambers, and the second chamber is with desks and windows (outlets), and when I start the simulation I don't know why Courant Number goes very high and Pimple iterations for velocity goes very high (1000 iterations!) .
Here are my docs about the case: fvSchemes Quote:
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December 21, 2020, 17:44 |
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#2 |
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Can you post the terminal output from the run? It's difficult to know what's failing without more detail. I have had similar issues in the past due to poorly configured pressure boundary conditions. Can you post your velocity and pressure files for time 0?
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December 21, 2020, 17:56 |
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#3 | |||
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Yes, this is the U file
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December 21, 2020, 18:25 |
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#4 |
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hmm, It looks to me to be failing on a Div/0 error while calculating epsilon. I notice in your solution file you have the relative tolerance for U|K|epsilon set to 0. I don't think this is the issue but try setting it to 0.1 and see if it solves.
For your pressure boundaries try setting your door, room, and desk to zeroGradient rather than fixed flux pressure and see if it helps. |
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December 21, 2020, 18:41 |
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#5 | |
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I tried to change to zeroGradient in pressure and I get this message:
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December 21, 2020, 18:52 |
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#6 |
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Try modifying your fvSolution file to include the reference pressure like this:
PIMPLE { momentumPredictor yes; nOuterCorrectors 3; nCorrectors 1; nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; } from this: PIMPLE { momentumPredictor yes; nOuterCorrectors 3; nCorrectors 1; nNonOrthogonalCorrectors 0; } |
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December 21, 2020, 19:01 |
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#7 | |
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Thanks, now it says that I should check my velocity boundary conditions as it's stated here:
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December 21, 2020, 19:12 |
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#8 |
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mmmm, well I am not super confident on this one but I suspect it may be due to your 0 pressure condition in your solution resulting in no mass flow at your outlet. if you set the outlet pressure to fixed uniform 100,000 and the internal field uniform to 100,000 in your pressure boundary file does it fix the problem? this would be equivalent to 1Bar pressure (atmospheric) for both the outlet condition and the initial condition.
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December 21, 2020, 19:21 |
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#9 |
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Yeah,but I don't now where I see if you put 0 in the pressure file it's equal to atmospheric pressure and on the other hand I think in pimpleFoam it's not very important pressure but p/density it is.
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December 21, 2020, 19:38 |
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#10 |
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Oh you're right, it's dynamic pressure so it shouldn't matter. For some reason it is setting your mass outflow to 0, not sure if this could be an issue with the way the outlet is defined, the pressureInletOutletVelocity should work unless it is considering the outflow to be backwards and limiting it to zero. will it execute if you set the outlet velocity boundary to zeroGradient?
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December 21, 2020, 19:44 |
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#11 |
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Same as before if I set the velocity boundary condition in the outlet as zeroGradient.
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December 21, 2020, 19:47 |
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#12 |
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hmm, sounds like it could be an issue with the boundary definition. can you go into the constant/polymesh/boundary file and post the contents?
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December 21, 2020, 19:51 |
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#13 | ||
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Yes, here it is
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December 21, 2020, 20:11 |
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#14 |
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Looks like it should be fine. I am really not sure what is going on, as far as I can see your configuration should work fine. How big is the simulation setup? are you able to zip and upload it?
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December 22, 2020, 10:24 |
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#15 |
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Yes, here are the different folders except the constant folder I can't upload it.0 (còpia).zip
system (còpia).zip Thanks in advance. |
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December 25, 2020, 17:26 |
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#16 |
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Hi,
I have the same issue in my case. pimplefoam converges but the courant number increases to very high values even in the first time steps. It seems that the resulted U values are incorrectly very high which lead to high Co#. |
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September 8, 2023, 05:52 |
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#17 |
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krishna kant
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Hi,
I ever faced a similar issue. Try setting up proper initial fields. It helps in stability a lot. 0 is a poor initial condition. |
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