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September 24, 2010, 12:34 
turbDyMFoam and Convergence

#1 
Senior Member
Robert
Join Date: Sep 2010
Posts: 158
Rep Power: 8 
Hello,
I have used icoDyMFoam to run a turbomachinery case (I was learning to use OpenFOAM, mesh, etc.), and obviously it did not converge. So I have been trying to implement turbDyMFoam. I have downloaded the files found here: http://openfoamwiki.net/index.php/Si...vaned_diffuser And transplanted the controlDict, RASProperties, transportProperties, fvsolution, and fvscheme files to my (originally icoDyMFoam) case. I also put boundary conditions on the inlet (freestream) flow (I am doing an external flow with a rotating part) for k and epsilon (zerogradient for everywhere else). The simulation runs at least, but soon diverges (floating point exception, huge velocity magnitudes). Can anybody give me a guide to the parameters I can adjust to get convergence? Thanks in advance. 

September 24, 2010, 15:17 

#2 
Senior Member
Robert
Join Date: Sep 2010
Posts: 158
Rep Power: 8 
I get these figures:
Code:
Largest slave weighting factor correction : 1.0817671 average: 1.0000028 Largest master weighting factor correction: 1 average: 1 It is actually running, and I am only getting floating point exceptions, so I guess that means only the initial conditions are bad. I have tried: http://www.cfdonline.com/Forums/ope...implefoam.html http://www.cfdonline.com/Forums/ope...pskreu.html None fail to diverge. Last edited by lordvon; September 24, 2010 at 16:54. 

September 24, 2010, 20:27 

#3 
Senior Member
Robert
Join Date: Sep 2010
Posts: 158
Rep Power: 8 
Hey guys,
Posting working cases of turbulent external flow using turbdymfoam would be highly appreciated. 

September 25, 2010, 07:13 

#4 
Senior Member
Andrea Pasquali
Join Date: Sep 2009
Location: Germany
Posts: 142
Rep Power: 9 
Hi lordvon,
I'm trying turbDyMFoam with ggi on wind turbine analysis and it's working well. I use RAS kOmegaSST turbulence model. Have you good mesh (especially in nonOrthoFaces check)? Are your turbulent parameters internalField values correct? Regards
__________________
Andrea Pasquali 

September 25, 2010, 19:03 

#5 
Senior Member
Robert
Join Date: Sep 2010
Posts: 158
Rep Power: 8 
Hello Andrea, thanks for your reply.
I ran 'checkMesh' and it said that one mesh check failed. I could not discern what exactly this was from the terminal outputs. 'Nonorthogonality check OK.' ; is this what you were talking about? I posted the entirety of the terminal message below. I have also posted below my initial condition files for k and epsilon. I calculated them using the common formulas. The boundary types in those files are not the only ones I have tested. Could I take a look at your fvsolution, fvscheme, and /0/ files for k, epsilon, and omega? Have you tried using RNGkepsilon? /0/k: Code:
dimensions [0 2 2 0 0 0 0]; internalField uniform 0.17; boundaryField { left { type zeroGradient; //type turbulentIntensityKineticEnergyInlet; //intensity 0.05; //value 1; } top { type zeroGradient; } right { type zeroGradient; } bottom { type zeroGradient; } outsideSlider { type ggi; } casing { type zeroGradient; } defaultFaces { type empty; } insideSlider { type ggi; } shaft { type zeroGradient; } blades { type zeroGradient; } } Code:
dimensions [0 2 3 0 0 0 0]; internalField uniform .67; boundaryField { left { type zeroGradient; //type turbulentMixingLengthDissipationRateInlet; //mixingLength 0.1; //value uniform 200; } top { type zeroGradient; } right { type zeroGradient; } bottom { type zeroGradient; } outsideSlider { type ggi; } casing { type zeroGradient; } defaultFaces { type empty; } insideSlider { type ggi; } shaft { type zeroGradient; } blades { type zeroGradient; } } Code:
Create time > FOAM Warning : From function dlLibraryTable::open(const fileName& functionLibName) in file db/dlLibraryTable/dlLibraryTable.C at line 86 could not load libOpenFoamTurbo.so: cannot open shared object file: No such file or directory Create polyMesh for time = constant Time = constant Mesh stats points: 72864 internal points: 0 faces: 248063 internal faces: 104627 cells: 70538 boundary patches: 10 point zones: 0 face zones: 2 cell zones: 2 Number of cells of each type: hexahedra: 0 prisms: 70538 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 0 polyhedra: 0 Checking topology... Boundary definition OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. *Number of regions: 2 The mesh has multiple regions which are not connected by any face. <<Writing region information to "constant/cellToRegion" Checking patch topology for multiply connected surfaces ... Patch Faces Points Surface topology left 37 76 ok (nonclosed singly connected) top 56 114 ok (nonclosed singly connected) right 37 76 ok (nonclosed singly connected) bottom 56 114 ok (nonclosed singly connected) outsideSlider 456 912 ok (nonclosed singly connected) casing 670 1340 ok (nonclosed singly connected) defaultFaces 141076 72864 ok (nonclosed singly connected) insideSlider 456 912 ok (nonclosed singly connected) shaft 16 32 ok (nonclosed singly connected) blades 576 1152 ok (nonclosed singly connected) Checking geometry... This is a 2D mesh Overall domain bounding box (1.125 1.125 0) (2.25 1.125 1) Mesh (nonempty) directions (1 1 0) Mesh (nonempty, nonwedge) dimensions 2 All edges aligned with or perpendicular to nonempty directions. Boundary openness (1.6291944e17 4.3115768e17 1.895701e23) Threshold = 1e06 OK. ***High aspect ratio cells found, Max aspect ratio: 3898.0533, number of cells 37146 Threshold = 1000 <<Writing 37146 cells with high aspect ratio to set highAspectRatioCells Minumum face area = 2.5918065e07. Maximum face area = 0.084123393. Face area magnitudes OK. Min volume = 2.5918065e07. Max volume = 0.0027079637. Total volume = 7.5688711. Cell volumes OK. Mesh nonorthogonality Max: 33.073843 average: 6.9423388 Threshold = 70 Nonorthogonality check OK. Face pyramids OK. Max skewness = 0.49352535 OK. Failed 1 mesh checks. End 

September 25, 2010, 21:18 
fvSolution tolerance and reltol

#6 
Senior Member
Robert
Join Date: Sep 2010
Posts: 158
Rep Power: 8 
Hello everyone,
Running komegaSST, I no longer get floating point exceptions (at least not yet). However looking at the output through paraFoam, things are still crazy. I stumbled upon this thread: http://www.cfdonline.com/Forums/ope...timesteps.html , I started to increase tolerance of p's reltol. That decreased the amount of bounding messages, though they still appear. So I was wondering, can anybody explain how to adjust the fields in fvSolution (preconditioner, tolerance, reltol) to get better convergence and accuracy? Here is a relative section in the OpenFOAM manual: http://www.openfoam.com/docs/user/fvSolution.php (I am looking into it myself of course, I put this up so that a solution may be worked towards in parallel) ADDITIONS: Ok, so I have decided to set all 'reltol's to zero, that way we only have to worry about the 'tolerance'. Do I need to mess with the preconditioners? My system files so far: fvSolution: Code:
solvers { pcorr PCG { preconditioner DIC; tolerance 1e10; relTol 0; }; p PCG { preconditioner DIC; tolerance 1e10; relTol 0; }; pFinal PCG { preconditioner DIC; tolerance 1e10; relTol 0; }; U PBiCG { preconditioner DILU; tolerance 1e10; relTol 0; }; k PBiCG { preconditioner DILU; tolerance 1e10; relTol 0; }; epsilon PBiCG { preconditioner DILU; tolerance 1e10; relTol 0; }; R PBiCG { preconditioner DILU; tolerance 1e10; relTol 0; }; omega PBiCG { preconditioner DILU; tolerance 1e10; relTol 0; }; } PISO { nCorrectors 3; nNonOrthogonalCorrectors 1; pRefCell 0; pRefValue 0; } Code:
ddtSchemes { default Euler; } gradSchemes { default Gauss linear; grad(p) Gauss linear; grad(U) Gauss linear; } divSchemes { default none; div(phi,U) Gauss upwind; div(phi,k) Gauss upwind; div(phi,epsilon) Gauss upwind; div(phi,omega) Gauss upwind; div(phi,R) Gauss upwind; div(R) Gauss linear; div(phi,nuTilda) Gauss upwind; div((nuEff*dev(grad(U).T()))) 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; laplacian(DREff,R) Gauss linear corrected; laplacian(DnuTildaEff,nuTilda) Gauss linear corrected; laplacian(DomegaEff,omega) Gauss linear corrected; laplacian((rho*(1A(U))),p) Gauss linear corrected; laplacian(alphaEff,h) Gauss linear corrected; laplacian(rAU,p) Gauss linear corrected; laplacian(nu,U) Gauss linear corrected; laplacian(1,p) Gauss linear corrected; } interpolationSchemes { default linear; interpolate(U) linear; } snGradSchemes { default corrected; } fluxRequired { default no; p; } Last edited by lordvon; September 25, 2010 at 21:51. 

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