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May 26, 2010, 16:14 

#21  
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Alberto Passalacqua
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Quote:
The upwind schemes does not require anything: div(phi, U) Gauss upwind; The gradient scheme is used, for example, by the linearUpwind scheme: div(phi, U) Gauss linearUpwind Gauss linear; Quote:
Best, 

May 26, 2010, 17:28 

#22 
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Moritz Wied
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hi alberto,
thanks a lot for your reply. i want to limit k and epsilon and dont know how to make that. e.g. for k, would it work like that? div(phi, k) Gauss linearUpwind Gauss limitedLinear 1e10 30; if not, could you give me an example? thanks a lot, Moritz 

May 26, 2010, 22:54 

#23  
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Alberto Passalacqua
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Quote:
If the equations do not include that physical limit, I would not use a limiter, but a bound, as done in the codes already. The syntax, explained at page U113 of the user's guide, is, for example: div(phi, U) Gauss limitedVanLeer a b; where a and b are the bounds of your range [a,b]. Schemes that support the limitation in this way are listed in the same page. Best, 

May 27, 2010, 05:08 

#24  
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Moritz Wied
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Quote:
What i dont understand is, that in these Schemes you calculate divergence and divgrad, but not the scalar values themselves, so can you limit the values themselves there? Quote:
Quote:
what parameters have to be given, when you use e.g. limitedVanLeerV? Thank you so much for your time!! 

May 27, 2010, 17:11 

#25  
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Alberto Passalacqua
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Quote:
Let's try to understand what is the cause. What solver are you using, what turbulence model, and what boundary condition setup? Best, 

May 27, 2010, 22:43 

#26 
Senior Member

Hi Alberto, I have a similar problem with my case using kOmegaSST model. However, I ran many different but similar meshes of this external flow and they all converge. Only this case diverges on k. All the BCs and other parameters are identical.
Also, the case runs fine in laminar, although it doesn't converge... Could my mesh be the only cause of the divergence? Thanks, Louis 

May 27, 2010, 23:10 

#27 
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Alberto Passalacqua
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Let me guess: is the mesh tetrahedral (maybe generated with Salomé)?
Please run checkMesh, and if you have very skewed cells and/or a high degree of nonorthogonality, yes, the mesh can be the reason of the problem. In this case you can easily see where this happens by saving solutions right before the crash and looking for peaks of values in the diverging variables. Best, 

May 28, 2010, 11:26 

#28 
Senior Member

Hi Alberto,
it is a hexmesh, from snappyHexMesh. Yes, it does have skewed faces but those skewed faces didn't seem to create a problem on my other meshes (well at least the bound on k worked for those other meshes). Thanks for your advice, I will try to slightly modify my snappyHexMesh parameters to get a slightly different mesh! Cheers, Louis 

May 28, 2010, 16:02 

#29  
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Alberto Passalacqua
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Quote:
Best, 

May 29, 2010, 10:18 

#30 
Senior Member

I got it to converge by modifying the mesh on the triSurface file.stl I gave to snappyHexMesh.. Not the best solution but works as a fix
Thx, Louis 

June 15, 2010, 10:27 
MRFSimpleFoam bounding k & epsilon

#31 
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Aldo Iannetti
Join Date: Feb 2010
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Hi Foamers,
I have a great problem using MRFSimpleFoam with OF 1.6. I'm studing (fluent Vs OpenFOAM) a 3D fan (mesh imported from GAMBIT) using the kepsilon model and upwind schemes for convective fluxes, the under relaxation factors are 0.3, 0.7, 0.5, 0.5 for pressure, velocity, k and epsilon. After 5600 iterations my OF residuals are very low and the message "bounding epsilon..." is printed very few times but the solution is far from the one obtained by Fluent using UDS. Trying to relaunch OF case from the 5600th iteration I faced the k and epsilon diverging and I haven't changed settings. I'm struggling to know what's going wrong.Can you please help me? Is there anybody who know about bugs in MRFSimpleFoam in OF 1.6? How to let kepsilon converge? Thanks Aldo 

June 15, 2010, 16:10 

#32 
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Alberto Passalacqua
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Hi,
we do not have enough details to answer. P.S. Please, when you have a question, open a new thread. Thanks! :) 

June 16, 2010, 04:01 

#33  
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Aldo Iannetti
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Quote:
Resume: MRFSimpleFoam 1st order upwind> convergence of u, p, k, epsilon untill 5800 iterations> stop and restart> residuals stepup (3 order) and divergence of k and epsilon (under zero) without any change in settings (I thought to get crazy but it's true). MRFSimpleFoam 2nd order upwind> divergence of k and epsilon (under zero), It seem there is not the possibility using other discretization schemes. How to set up a 2nd order disc. scheme without any problem? Is there anybody who know have tested MRFSimpleFoam comparing it to fluent? How arethe resulting fields? Thanks aldo 

June 16, 2010, 10:48 

#34  
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Alberto Passalacqua
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Quote:
You might want to try


June 16, 2010, 12:15 

#35  
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Aldo Iannetti
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Quote:
Sorry, I'm quite new in OF, can you please correct my fvSchemes dict (expecially the laplacian schemes)? __________________________________________________ ______ ddtSchemes { default steadyState; } gradSchemes { default cellLimited Gauss linear 1; grad(p) cellLimited Gauss linear 1; grad(U) cellLimited Gauss linear 1; } divSchemes { default none; div(phi,U) Gauss linearUpwindV cellMDLimited Gauss linear 1; div(phi,k) Gauss linearUpwind cellLimited Gauss linear 1; div(phi,epsilon) Gauss linearUpwind cellLimited Gauss linear 1; div((nuEff*dev(grad(U).T()))) Gauss linearUpwind cellLimited Gauss linear 1;//Gauss linear; } laplacianSchemes { default none; laplacian(nuEff,U) Gauss linear corrected; laplacian((1A(U)),p) Gauss linear corrected; laplacian(DkEff,k) Gauss linear corrected; laplacian(DepsilonEff,epsilon) Gauss linear corrected; } interpolationSchemes { default linear; interpolate(U) linear; } snGradSchemes { default corrected; } fluxRequired { default no; p ; } __________________________________________________ ___ Thanks 

June 19, 2010, 12:33 
MRF Divergence

#36 
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Aldo Iannetti
Join Date: Feb 2010
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Hi Alberto,
I tried to follow your advices but It diverges after 4000 iter. and I don't understand why, can you please have a look at the attached log and fvSchemes files in order to correct my mistakes? Thanks Aldo 

June 20, 2010, 15:10 

#37 
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Alberto Passalacqua
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Are there zones of the system where you can observe some unphysical behaviour (velocity too high, for example?
Additionally, what underrelaxation factors are you using? Did you try to reduce them for k and epsilon? P.S. You wrote you use OpenFOAM 1.6. Did you update it to 1.6.x? Best, 

February 5, 2014, 13:01 
How can I bound own Scalar value in equations?

#38 
New Member
Mahdi
Join Date: Jul 2013
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Thanks all for information about bounded schemes
I need a method to bound own volScalarField that is solved in an equation has div , laplacian ,... for example C1 in the concentration equation must be between [0,1] anybody can tell me how can i add this limiter to the equation and force C1 to be in [0,1]? thank you. 

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