# fvschemes and fvsolutions in MRFSimpleFoam

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 November 24, 2009, 10:07 fvschemes and fvsolutions in MRFSimpleFoam #1 Member   任芸 Join Date: Jun 2009 Posts: 75 Rep Power: 8 hi all, i use MRFSimplefoam to study a centrifugal pump impeller study.the problem is :after several steps of iterations,i have a Floating exception error,due to the fast increase in epsilon and k values.during the calculation,i keep the fvschemes and fvsolutions unchanged,so i guess they maybe the cause to divergenced. fvschemes: FoamFile { version 2.0; format ascii; class dictionary; object fvSchemes; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // ddtSchemes { default steadyState; } gradSchemes { default Gauss linear; grad(p) Gauss linear; grad(U) Gauss linear; } divSchemes { default none; div(phi,U) Gauss limitedLinearV 1; div(phi,k) Gauss limitedLinear 1; div(phi,epsilon) Gauss limitedLinear 1; div((nuEff*dev(grad(U).T()))) Gauss linear; } laplacianSchemes { default none; laplacian(nuEff,U) Gauss linear corrected; laplacian((1|A(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; } // ************************************************** *********************** // fvsolutions: FoamFile { version 2.0; format ascii; class dictionary; object fvSolution; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // solvers { p GAMG { tolerance 1e-8; relTol 0.05; smoother GaussSeidel; cacheAgglomeration true; nCellsInCoarsestLevel 20; agglomerator faceAreaPair; mergeLevels 1; }; U smoothSolver { smoother GaussSeidel; nSweeps 2; tolerance 1e-7; relTol 0.1; }; k smoothSolver { smoother GaussSeidel; nSweeps 2; tolerance 1e-7; relTol 0.1; }; epsilon smoothSolver { smoother GaussSeidel; nSweeps 2; tolerance 1e-7; relTol 0.1; }; } SIMPLE { nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; } relaxationFactors { p 0.3; U 0.5; k 0.5; epsilon 0.5; } // ************************************************** *********************** // could you please tell me how can i resolve it? thank you yours jennifer

 November 25, 2009, 03:24 #2 Senior Member   Gijsbert Wierink Join Date: Mar 2009 Posts: 382 Rep Power: 9 Hi Jennifer, You could try to decrease the relaxation factor of k and epsilon and check that the time step is small enough. __________________ Regards, Gijs

 November 25, 2009, 08:37 #3 Member   任芸 Join Date: Jun 2009 Posts: 75 Rep Power: 8 thank you Gijs, after i change the relaxation factor 0.25 for turbulence properties.0.5 for velocity, 0.1 for pressure,and it iterate more steps than before.but it divergenced at last ,also due to the fast increase in epsilon and k values. appreciate! jennifer

 November 25, 2009, 10:31 #4 Senior Member   Gijsbert Wierink Join Date: Mar 2009 Posts: 382 Rep Power: 9 You're very welcome, glad to help. Another thing may be the number of cells in the coarsest level for the pressure solver. In the tutorials this is usually some low number because the grid is commonly good. If you have a more complex grid with some weird and/or skewed cells it works to increase that number, that is increase Code: `nCellsInCoarsestLevel 20;` to e.g. Code: `nCellsInCoarsestLevel 500;` But note that the number cannot be too high, then the solver will complain. kiddmax and bennn like this. __________________ Regards, Gijs

 November 25, 2009, 11:28 #5 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 9 Hi Renyun: would you mind show me the information of last iteration ? i mean which one is first go to diverge.

November 25, 2009, 23:30
#6
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Join Date: Jun 2009
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Quote:
 Originally Posted by waynezw0618 Hi Renyun: would you mind show me the information of last iteration ? i mean which one is first go to diverge.
Hello Doctor Zhang wei,
the last iteration is as follows:
Time = 16

smoothSolver: Solving for Ux, Initial residual = 0.0146841, Final residual = 0.00071266, No Iterations 2
smoothSolver: Solving for Uy, Initial residual = 0.00278712, Final residual = 0.00015971, No Iterations 2
smoothSolver: Solving for Uz, Initial residual = 0.000257914, Final residual = 3.3909e-06, No Iterations 2
GAMG: Solving for p, Initial residual = 4.86694e-06, Final residual = 1.07195e-07, No Iterations 2
time step continuity errors : sum local = 2.70395e+23, global = 8.88956e+22, cumulative = 8.88956e+22
smoothSolver: Solving for epsilon, Initial residual = 1, Final residual = 0.00258025, No Iterations 2
bounding epsilon, min: -2.59328e+36 max: 9.99446e+45 average: 2.25125e+40
smoothSolver: Solving for k, Initial residual = 0.00087545, Final residual = 8.77668e-07, No Iterations 2
bounding k, min: -7.27788e+35 max: 2.9925e+38 average: 6.85609e+32
ExecutionTime = 575.49 s ClockTime = 588 s

after the 17th step ,it divergenced!
several days ago,i have a structured impeller meshed in CFX calculated by MRFSimpleFoam.but it divergenced again,so i guess there maybe something wrong with my setup,could you mind to help me?
regards！
renyun

 November 26, 2009, 03:51 #7 Member   Join Date: Nov 2009 Posts: 33 Rep Power: 7 Hi Renyun, I would try to start with simple Upwind for turbulence first: So: div(phi,k) Gauss upwind; div(phi,epsilon) Gauss upwind; div((nuEff*dev(grad(U).T()))) Gauss upwind; And than switch to higher order schemes maybe later. But from my experience this is often not needed for turbulence to use higher order schemens, but of course for div(phi,U). Also I think that in Simple alg. the underrelaxation for U+p should be "1". So maybe it helps to adapt the underrelaxation. Hope this helps. Stawrogin

November 26, 2009, 03:52
#8
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Gijsbert Wierink
Join Date: Mar 2009
Posts: 382
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Quote:
 bounding epsilon, min: -2.59328e+36 max: 9.99446e+45 average: 2.25125e+40 smoothSolver: Solving for k, Initial residual = 0.00087545, Final residual = 8.77668e-07, No Iterations 2 bounding k, min: -7.27788e+35 max: 2.9925e+38 average: 6.85609e+32
Clearly epsilon and k explode. What are your initial and boundary conditions for epsilon and k?
__________________
Regards, Gijs

 November 26, 2009, 04:55 #9 Member   任芸 Join Date: Jun 2009 Posts: 75 Rep Power: 8 hello Gijs, the epsilon and k initial values are: FoamFile { version 2.0; format ascii; class volScalarField; object epsilon; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -3 0 0 0 0]; internalField uniform 0.45; boundaryField { wall { type zeroGradient; } Outlet { type zeroGradient; } Inlet { type fixedValue; value uniform 0.45; } } FoamFile { version 2.0; format ascii; class volScalarField; object k; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -2 0 0 0 0]; internalField uniform 0.09; boundaryField { wall { type zeroGradient; } Outlet { type zeroGradient; } Inlet { type fixedValue; value uniform 0.09; } } by the way,the values of k and epsilon calculate by the following eaquations: Last edited by renyun0511; November 26, 2009 at 07:38.

 November 26, 2009, 05:20 #10 Senior Member   Gijsbert Wierink Join Date: Mar 2009 Posts: 382 Rep Power: 9 Hi Renyun, Usually it helps to have the k and epsilon values for the internalField lower (by, say, a factor of 10) than the inlet values. Also, I'd try to play a bit with the schemes, as stawrogin suggests. __________________ Regards, Gijs

November 26, 2009, 22:09
#11
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Quote:
 Originally Posted by stawrogin Hi Renyun, I would try to start with simple Upwind for turbulence first: So: div(phi,k) Gauss upwind; div(phi,epsilon) Gauss upwind; div((nuEff*dev(grad(U).T()))) Gauss upwind; And than switch to higher order schemes maybe later. But from my experience this is often not needed for turbulence to use higher order schemens, but of course for div(phi,U). Also I think that in Simple alg. the underrelaxation for U+p should be "1". So maybe it helps to adapt the underrelaxation. Hope this helps. Stawrogin
Thank you very much Stawrogin,
i can continue the calculation after adopting your advice.As you known,the problem has puzzled me since two months ago.it is indeed a good news to me that it's not divergenced again!i am extremely grateful to you,and to all people helped me.
and there are some problem :
1.the original divSchemes set is:
divSchemes
{
default none;
div(phi,U) Gauss limitedLinearV 1;
div(phi,k) Gauss limitedLinear 1;
div(phi,epsilon) Gauss limitedLinear 1;
}

i don't know the difference between Gauss upwind and Gauss limitedLinear.why is Gauss?and which in Fluent is one/two order upwind(i know).
2.in Simple alg. why the underrelaxation for U+p should be "1"? the following i changed is：
relaxationFactors
{
p 0.3;
U 0.5;
k 0.5;
epsilon 0.5;
}

yours

jennifer
appreciate!

May 17, 2011, 02:48
#12
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Kurne
Join Date: Aug 2010
Location: Pune, INDIA
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Dear 任芸

I am facing similar problem what u have face and mentioned here.

I have followed the guidance mentioned by stawrogin but still i am facing same problem.Will u please guide me.

Attached Files
 schemes.tar.gz (897 Bytes, 15 views)
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June 25, 2011, 06:36
MRFSimpleFoam divergence
#13
Member

Aldo Iannetti
Join Date: Feb 2010
Posts: 48
Rep Power: 7
Quote:
 Originally Posted by gwierink You're very welcome, glad to help. Another thing may be the number of cells in the coarsest level for the pressure solver. In the tutorials this is usually some low number because the grid is commonly good. If you have a more complex grid with some weird and/or skewed cells it works to increase that number, that is increase Code: `nCellsInCoarsestLevel 20;` to e.g. Code: `nCellsInCoarsestLevel 500;` But note that the number cannot be too high, then the solver will complain.
Hi,
I'm facing an issue using MRFSimpleFoam simulting a centrifugal pump, I see the divergence just when the residual seem to come low enough to think to be out of problems, have a kook to the image, (p residual is missing but it behaves just like the others). The divergence occurs within 2 iteration only and I'm not able to understand which field causes the problem, here attached fvSchemes and fvSolution.
Thanks

Aldo
Attached Images
 Immagine.jpg (56.6 KB, 36 views)
Attached Files
 fvSchemes.txt (2.0 KB, 35 views) fvSolution.txt (1.9 KB, 23 views)

June 26, 2011, 02:55
#14
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Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
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Quote:
 Originally Posted by aldo.iannetti Hi, I'm facing an issue using MRFSimpleFoam simulting a centrifugal pump, I see the divergence just when the residual seem to come low enough to think to be out of problems, have a kook to the image, (p residual is missing but it behaves just like the others). The divergence occurs within 2 iteration only and I'm not able to understand which field causes the problem, here attached fvSchemes and fvSolution. Thanks Aldo
I would suggest to the attached setup. If you have problems with it, try to run first a laminar simulation, to understand if the turbulence model is giving you troubles.

Also, run checkMesh on your grid to check its quality.

Best,
Attached Files
 fvSchemes.txt (1.7 KB, 61 views) fvSolution.txt (1.8 KB, 52 views)
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June 26, 2011, 04:02
MRFSimpleFoam issue
#15
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Aldo Iannetti
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Quote:
 Originally Posted by alberto I would suggest to the attached setup. If you have problems with it, try to run first a laminar simulation, to understand if the turbulence model is giving you troubles. Also, run checkMesh on your grid to check its quality. Best,
OK,
Here attached the set-up files, I've tried to remesh the domain and (since the last post was about a GGI interface mesh using OpenFOAM 1.6 ext) tried to use OF 1.7.1 without GGI (even if I need it for the next simulations). Now I'm facing convergence but with a very strange problem: I see that the solutor has imposed a 0 velocity in the inlet BC even if I set up a 3.9 m/s vel.
1) Why is that?
2) Can I set up different BC?
3) Have I miss something?
4) Can GGI be the cause of the sudden divergence I mentioned in the last post? (checking GGI mesh had no problem)

Thanks
Aldo
Attached Files
 Case.zip (67.7 KB, 27 views)

 June 26, 2011, 04:18 #16 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,894 Rep Power: 26 From your figure, it seems you impose U tangentially at the inlet, since the inlet seems parallel to z, and your velocity at the inlet is parallel to z. Also, the case is not complete. I do not have experience with GGI, so I cannot answer to the rest. Best, __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image. OpenQBMM - An open-source implementation of quadrature-based moment methods

June 26, 2011, 04:27
#17
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Aldo Iannetti
Join Date: Feb 2010
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Quote:
 Originally Posted by alberto From your figure, it seems you impose U tangentially at the inlet, since the inlet seems parallel to z, and your velocity at the inlet is parallel to z. Also, the case is not complete. I do not have experience with GGI, so I cannot answer to the rest. Best,
I just had a look to the case and I'm sure the inlet is perpendicular to the z axis and I've imposed a +z velocity of 3.9 m/s. Do You think using a mass flow inlet BC would be lucky enough to ensure the velocity at inlet of 3.9 m/s? Why can't it keep the velocity I've imposed? Is it allowed to do that?

 June 26, 2011, 04:36 #18 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,894 Rep Power: 26 Hi, no, with a fixedValue BC, the code does not change the BC at all. You probably have some problem elsewhere. P.S. If you look at the figure WaterPump.jpg in your attachment, the inlet does not seem perpendicular to z. :-) __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image. OpenQBMM - An open-source implementation of quadrature-based moment methods

June 26, 2011, 20:42
#19
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Quote:
 Originally Posted by aldo.iannetti OK, Here attached the set-up files, I've tried to remesh the domain and (since the last post was about a GGI interface mesh using OpenFOAM 1.6 ext) tried to use OF 1.7.1 without GGI (even if I need it for the next simulations). Now I'm facing convergence but with a very strange problem: I see that the solutor has imposed a 0 velocity in the inlet BC Aldo
hi aldo,
From the picture of your pump model and the setup of your case, i guess may your problem is that you ingored the setup of GGI. The rotating impeller and stationary volute need to be coupled and GGI does work.
Additionally, the residuals seem not converged. so i suggest you can reset your fvsolution file.
eg.
relaxationFactors
{
p 0.5;
U 0.5;
k 0.3;
epsilon 0.3;
}
Good luck!

 August 1, 2011, 08:35 #20 New Member   Suhas Join Date: Jul 2011 Location: Pune Posts: 20 Rep Power: 5 hi foamers, please tell me that is ggi boundary conditions work with OF 1.7.1? and for my pump case i am converting star ccm+ mesh file i.e. .ccm file. There is one wrongOrientedFace while doing checkMesh. if anybody know how to solve this then help me. or what are the precaustions to be taken while importing ccm+ file to OF 1.7.1. to useful for MRFSimpleFoam?

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