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April 21, 2012, 21:25 |
singularity?
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#1 |
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Mihai Pruna
Join Date: Apr 2010
Location: Boston
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I am trying to model a simple pipe with total pressure at inlet and fixed 0 pressure at outlet. Tried various things, last one being a filleting of the edges.
Please see images. Flat face facing you is inlet,curved faces are wall and there is symmetry on the Z=0 plane. I pasted the BCs,o refer to this post: http://www.cfd-online.com/Forums/ope...ty-driven.html I am attaching screenshots. I already tried smaller relaxation factors. still got huge values. FoamFile { version 2.0; format ascii; class volScalarField; location "0"; object nut; } dimensions [0 2 -1 0 0 0 0]; internalField uniform 0; boundaryField { rightZmax { type freestream; freestreamValue uniform 0; } leftZmin { type symmetryPlane; } inletXmin { type freestream; freestreamValue uniform 0; } outletXmax { type calculated; value uniform 0; } topYmax { type freestream; freestreamValue uniform 0; } bottomYmin { type freestream; freestreamValue uniform 0; } Sductface1 { type nutkWallFunction; value uniform 0; } Sductface2 { type nutkWallFunction; value uniform 0; } SDuctInlet { type calculated; value uniform 0; } SDuctOutlet { type calculated; value uniform 0; } Sductface5 { type nutkWallFunction; value uniform 0; } Sductface6 { type nutkWallFunction; value uniform 0; } Sductface7 { type nutkWallFunction; value uniform 0; } Sductface8 { type nutkWallFunction; value uniform 0; } } FoamFile { version 2.0; format ascii; class volScalarField; object k; } dimensions [0 2 -2 0 0 0 0]; internalField uniform 0.240000; boundaryField { outletXmax { type inletOutlet; inletValue $internalField; value $internalField; } inletXmin { type freestream; freestreamValue uniform 0.240000; } bottomYmin { type freestream; freestreamValue uniform 0.240000; } topYmax { type freestream; freestreamValue uniform 0.240000; } leftZmin { type symmetryPlane; } rightZmax { type freestream; freestreamValue uniform 0.240000; } Sductface1 { type kqRWallFunction; value $internalField; } Sductface2 { type kqRWallFunction; value $internalField; } SDuctInlet { type fixedValue; value uniform 0.240000; } SDuctOutlet { type zeroGradient; } Sductface5 { type kqRWallFunction; value $internalField; } Sductface6 { type kqRWallFunction; value $internalField; } Sductface7 { type kqRWallFunction; value $internalField; } Sductface8 { type kqRWallFunction; value $internalField; } } FoamFile { version 2.0; format ascii; class volVectorField; location "0"; object U; } dimensions [0 1 -1 0 0 0 0]; internalField uniform (0.000000 0.000000 0.000000); boundaryField { inletXmin { type freestream; freestreamValue uniform (0.000000 0.000000 0.000000); } outletXmax { type inletOutlet; inletValue $internalField; value $internalField; } bottomYmin { type freestream; freestreamValue uniform (0.000000 0.000000 0.000000); } topYmax { type freestream; freestreamValue uniform (0.000000 0.000000 0.000000); } rightZmax { type freestream; freestreamValue uniform (0.000000 0.000000 0.000000); } leftZmin { type symmetryPlane; } Sductface1 { type fixedValue; value uniform (0 0 0); } Sductface2 { type fixedValue; value uniform (0 0 0); } SDuctInlet { type zeroGradient; } SDuctOutlet { type zeroGradient; } Sductface5 { type fixedValue; value uniform (0 0 0); } Sductface6 { type fixedValue; value uniform (0 0 0); } Sductface7 { type fixedValue; value uniform (0 0 0); } Sductface8 { type fixedValue; value uniform (0 0 0); } } FoamFile { version 2.0; format ascii; class volScalarField; object omega; } dimensions [0 0 -1 0 0 0 0]; internalField uniform 1.780000; boundaryField { inletXmin { type freestream; freestreamValue uniform 1.780000; } outletXmax { type inletOutlet; inletValue $internalField; value $internalField; } bottomYmin { type freestream; freestreamValue uniform 1.780000; } topYmax { type freestream; freestreamValue uniform 1.780000; } leftZmin { type symmetryPlane; } rightZmax { type freestream; freestreamValue uniform 1.780000; } Sductface1 { type omegaWallFunction; value $internalField; } Sductface2 { type omegaWallFunction; value $internalField; } SDuctInlet { type fixedValue; value uniform 1.780000; } SDuctOutlet { type zeroGradient; } Sductface5 { type omegaWallFunction; value $internalField; } Sductface6 { type omegaWallFunction; value $internalField; } Sductface7 { type omegaWallFunction; value $internalField; } Sductface8 { type omegaWallFunction; value $internalField; } } FoamFile { version 2.0; format ascii; class volScalarField; object p; } dimensions [0 2 -2 0 0 0 0]; internalField uniform 0.000000; boundaryField { inletXmin { type freestreamPressure; freestreamValue 0.000000; } outletXmax { type fixedValue; value $internalField; } bottomYmin { type freestreamPressure; freestreamValue 0.000000; } topYmax { type freestreamPressure; freestreamValue 0.000000; } leftZmin { type symmetryPlane; } rightZmax { type freestreamPressure; freestreamValue 0.000000; } Sductface1 { type zeroGradient; } Sductface2 { type zeroGradient; } SDuctInlet { type totalPressure; gamma 1.4; p0 uniform 100000.000000; } SDuctOutlet { type fixedValue; value uniform 0.000000; } Sductface5 { type zeroGradient; } Sductface6 { type zeroGradient; } Sductface7 { type zeroGradient; } Sductface8 { type zeroGradient; } } FoamFile { version 2.0; format ascii; class dictionary; object fvSolution; } solvers { p { solver GAMG; tolerance 1e-7; relTol 0.1; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; cacheAgglomeration on; agglomerator faceAreaPair; nCellsInCoarsestLevel 10; mergeLevels 1; } U { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; } k { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; } omega { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; } } SIMPLE { nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; residualControl { p 1e-5; U 1e-5; k 1e-5; omega 1e-5; } } potentialFlow { nNonOrthogonalCorrectors 10; pRefCell 0; pRefValue 0; } relaxationFactors { p 0.3; U 0.7; k 0.7; omega 0.7; } cache { grad(U); }
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April 22, 2012, 03:34 |
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#2 |
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Alberto Passalacqua
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At a first sight, there could be something wrong in a group of cells (the red area). What discretization schemes are you using? If you have problematic cells, turn limiters on to see if the situation improves.
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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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April 23, 2012, 15:17 |
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#3 |
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Mihai Pruna
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Location: Boston
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well, this is what i have in my fv schemes, copied from the motorbike tutorial.
will this work for internal flows as well? My solution seems to blow up only when I try to specify inlet pressure. FoamFile { version 2.0; format ascii; class dictionary; object fvSchemes; } ddtSchemes { default steadyState; } gradSchemes { default Gauss linear; } divSchemes { default none; div(phi,U) Gauss linearUpwindV grad(U); div(phi,k) Gauss upwind; div(phi,omega) Gauss upwind; div((nuEff*dev(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } fluxRequired { default no; p; }
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April 23, 2012, 16:49 |
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#4 |
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Alberto Passalacqua
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Yes, but it might help to put a limiter on the gradients too:
Code:
gradSchemes { default cellLimited Gauss linear 1; }
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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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April 23, 2012, 17:36 |
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#5 |
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Mihai Pruna
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Location: Boston
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Thanks for the suggestions. checkmesh returned all clear.
hmm, my numbers are too big too....been focused on the numerics didn't bother to check Bernoulli. 100000 deltap/rho gives supersonic velocity...and I was using simpleFoam....gonna try with 10000 instead.
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April 24, 2012, 18:18 |
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#6 |
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Mihai Pruna
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Location: Boston
Posts: 195
Rep Power: 16 |
thanks Alberto, the cell limiter helped prevent the values from attaining huge values.
However, I discovered another issue with my patches, which I fixed and I am hoping the simulation will run properly without limiters.
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