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November 18, 2016, 23:56 |
Courant number in OpenFOAM
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#1 |
New Member
Felix
Join Date: Sep 2015
Location: Hannover, Berlin
Posts: 23
Rep Power: 10 |
When do i need the folowing equation?
And what does it mean? is there Delta V the cell volume and Delta S a area from the cell surface? What means the f in sum_f. Could somebody explain it with a cell with the size a*b*c found it on: https://openfoamwiki.net/index.php/Co and also in CourantNo.C Code:
tmp<volScalarField::Internal> Coi Code:
( byRho ( (0.5*mesh_.time().deltaT()) *fvc::surfaceSum(mag(phi))()() /mesh_.V() ) ); |
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November 21, 2016, 02:52 |
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#2 |
Senior Member
Kevin van As
Join Date: Sep 2014
Location: TU Delft, The Netherlands
Posts: 252
Rep Power: 20 |
The Courant number provides a stability criterion, which is especially important if you use an explicit time scheme. If , you may expect your simulation to diverge. See:
https://en.wikipedia.org/wiki/Couran...Lewy_condition Intuitively, it says that within a given timestep , fluid may flow a distance of one cell at most (if ). In practice, we limit the Courant number to be smaller than 0.1~0.5. In your equation , where is the surface area of a face. Plugging in your , you will find that (for example). This expression should be evaluated for each face , because (again, see the link above) in more dimensions you should sum the contributions of each dimension. The factor 0.5 is presumably there to prevent double-counting opposite faces (west and east), as they belong to the same direction. When do you need it? You don't. In controlDict, set Code:
adjustTimeStep yes; maxCo 0.25; |
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November 21, 2016, 04:39 |
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#3 |
New Member
Felix
Join Date: Sep 2015
Location: Hannover, Berlin
Posts: 23
Rep Power: 10 |
Well this is everything i need t know. Thank you.
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July 1, 2018, 16:45 |
Automatic Control of Courant Number
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#4 | |
Member
Chris Harding
Join Date: Dec 2016
Posts: 76
Rep Power: 9 |
Quote:
Thanks in advance. Last edited by HappyS5; July 1, 2018 at 17:54. Reason: More descriptive |
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June 26, 2020, 05:04 |
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#5 |
Member
alexander thierfelder
Join Date: Dec 2019
Posts: 71
Rep Power: 6 |
The factor of 0.5 is just because we summed over the magnitude of the phi, since the phi_in hast to be equal to phi_out. Is that correct?
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June 26, 2020, 06:04 |
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#6 |
Senior Member
Join Date: Dec 2019
Location: Cologne, Germany
Posts: 355
Rep Power: 8 |
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June 28, 2021, 02:00 |
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#7 | |
Senior Member
Franco
Join Date: Nov 2019
Location: Compiègne, France
Posts: 129
Rep Power: 6 |
Quote:
icoFoam has not this feautre implemented, if you want "icoFoam with adjustable time" you should run pimpleFoam in ico foam setting and pimple has adjustable time build in. best regards |
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