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December 24, 2015, 08:37 |
Courant number explodes
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#1 |
Member
Evangelos
Join Date: Sep 2011
Posts: 87
Rep Power: 14 |
Hello Foamers!
i am trying to simulate the bifurcation that is depicted in the bifurcation.png file. There is one inlet in the right of the geometry and three outlets at the right. I use icoFoam to solve the flow problem. the deltaT is 1e-4. The courant number at first is very small but is increased with a small step after each iteration. After 10000 iterations the courant number is getting too big so the simulation stops. The mesh is ok after checkMesh. I calculate the Dp in order to have the desired mean velocity in the pipe before the bifurcation and then i divide with density. 0/p File object p; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; boundaryField { inlet { type fixedValue; value uniform 0.012957446; } outlet_internal { type fixedValue; value uniform 0; } outlet_externalbig { type fixedValue; value uniform 0; } outlet_externalsmall { type fixedValue; value uniform 0; } walls { type zeroGradient; } } 0/U File object U; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 1 -1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { inlet { type pressureInletVelocity; value uniform (0 0 0); } outlet_internal { type zeroGradient; } outlet_externalbig { type zeroGradient; } outlet_externalsmall { type zeroGradient; } walls { type fixedValue; value uniform (0 0 0); } } transportproperties transportModel Newtonian; nu nu [ 0 2 -1 0 0 0 0 ] 0.000002057; Can anyone help me to solve the problem ? I stuck over 15 days |
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December 24, 2015, 11:49 |
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#2 |
Member
Akshay Kumar
Join Date: Aug 2010
Location: India
Posts: 84
Rep Power: 15 |
Hey
Why are you running a transient simulation for this case? |
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December 24, 2015, 14:33 |
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#3 |
Member
Evangelos
Join Date: Sep 2011
Posts: 87
Rep Power: 14 |
I know that Poiseuille flow is treated as steady state.
But i have developed a code based on transient solver and i need to evaluate the results of my case with experimental data |
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December 25, 2015, 05:06 |
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#4 |
Member
Akshay Kumar
Join Date: Aug 2010
Location: India
Posts: 84
Rep Power: 15 |
Ahh okay. Did you try running adjustable time stepping? Also, try pimplefoam solver : use higher outerCorrectors and relax the solution
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December 25, 2015, 23:36 |
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#5 |
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,912
Rep Power: 36 |
If you know the desired velocity at the inlet, just impose that, rather than the pressure at the inlet (it seems you use that to find the pressure drop?).
Also, as a suggestion, I would not recommend icoFoam. You could use pimpleFoam, and have better control on the solution process (outer correctors, adaptive time-step, under-relaxation, ...).
__________________
Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. |
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