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-   -   Problem with steadyState solvers using pressure BC (http://www.cfd-online.com/Forums/openfoam/70905-problem-steadystate-solvers-using-pressure-bc.html)

 Victor December 9, 2009 09:41

Problem with steadyState solvers using pressure BC

Hi at all,

i have a problem, trying to reach a steadyState for my Case.
It is quite similar to the MultiRegionHeater Tutorial Case.
I fixed the pressure on the Inlet and the Outlet (fixedValue 1e5) and set the Velocity to zeroGradient on the Inlet and Outlet.
I tried different Solvers (rhoSimpleFoam, buoyantSimpleFoam) but always the problem occured, that the pressure Equation could not be solved properly. The residuals rised instead of converging......
Doas anybody know how to handle this?
Perhaps the problem is, that on the other boundaries i don't have a buoyantPressure BC as in the tutorial case!?
Victor

 woody December 14, 2009 06:40

1 Attachment(s)
Hi,

I do also have a similar Problem,

Global dimensions are (x y z) in mm: (60 1 1). In the center I have a square duct of 5 mm length, which tapers the chanel from h=1mm to H=0.8 mm.
My global resolutions are (141 17 17) cells within refinement near the wall.

solver: any Simple Solver
conditions:
• zeroGradient for p&U at all boundaries with normals in y&z direction
• U: fixedValue (0 0 0) at the central tapering p zeroGradient
• Inlet U: fixedValue (0 0 0) p zeroGradient
• Outlet p: fixedValue 1e5 U zeroGradient
fvSolution:

Code:

```      U     {         solver          PBiCG;         preconditioner  DILU;         tolerance        1e-05;         relTol          0;     }; p     {         solver          GAMG;         //preconditioner        DIC;         tolerance        1e-8;         relTol          1e-3;         smoother        GaussSeidel;         nPreSweeps      0;         nPostSweeps      2;         cacheAgglomeration on;         nCellsInCoarsestLevel 500;         agglomerator    faceAreaPair;         mergeLevels      3;     }; SIMPLE {     nNonOrthogonalCorrectors 5;     pRefCell        0;     pRefValue      1e5;     pMin pMin [ 1 -1 -2 0 0 0 0 ]  99000; } relaxationFactors {     p              0.3;     U              0.7;  }```
fvSchemes:
Code:

```ddtSchemes {     default steadyState; } gradSchemes {     default        Gauss linear; } divSchemes {     default        Gauss linear; } laplacianSchemes {     default        Gauss linear corrected; } interpolationSchemes {     default        linear; } snGradSchemes {     default        corrected; } fluxRequired {     default        no;     p; }```
But even potentialFoam comes up with:

Code:

```/*---------------------------------------------------------------------------*\ | =========                |                                                | | \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          | |  \\    /  O peration    | Version:  1.6.x                                | |  \\  /    A nd          | Web:      www.OpenFOAM.org                      | |    \\/    M anipulation  |                                                | \*---------------------------------------------------------------------------*/ Build  : 1.6.x-75be59b10850 Exec  : potentialFoam -writep Date  : Dec 14 2009 Time  : 10:24:17 Host  : mallorca PID    : 1295 Case  : /nfs/home/holzinger/OpenFOAM/holzinger-1.6.x/run/tests/LaplacianTest nProcs : 1 SigFpe : Enabling floating point exception trapping (FOAM_SIGFPE). // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Create time Create mesh for time = 0 Reading field p Reading field U Calculating potential flow GAMG:  Solving for p, Initial residual = 1, Final residual = 6.765909e-05, No Iterations 1 GAMG:  Solving for p, Initial residual = 0.919474, Final residual = 0.0009191767, No Iterations 309 GAMG:  Solving for p, Initial residual = 0.9116319, Final residual = 0.0009114059, No Iterations 898 GAMG:  Solving for p, Initial residual = 0.8729049, Final residual = 0.004903195, No Iterations 1000 GAMG:  Solving for p, Initial residual = 0.6403362, Final residual = 0.04555466, No Iterations 1000 GAMG:  Solving for p, Initial residual = 0.3767028, Final residual = 0.1098806, No Iterations 1000 continuity error = 0.1176216 Interpolated U error = 9.739145e-09 ExecutionTime = 288.06 s  ClockTime = 292 s End```
So obviously the pressure can't be computed although the solution should be trivial p=const allover the field...

chekMesh says:

Code:

```/*---------------------------------------------------------------------------*\ | =========                |                                                | | \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          | |  \\    /  O peration    | Version:  1.6.x                                | |  \\  /    A nd          | Web:      www.OpenFOAM.org                      | |    \\/    M anipulation  |                                                | \*---------------------------------------------------------------------------*/ Build  : 1.6.x-75be59b10850 Exec  : checkMesh Date  : Dec 14 2009 Time  : 11:37:05 Host  : mallorca PID    : 4495 Case  : /nfs/home/holzinger/OpenFOAM/holzinger-1.6.x/run/tests/LaplacianTest nProcs : 1 SigFpe : Enabling floating point exception trapping (FOAM_SIGFPE). // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Create time Create polyMesh for time = 0 Time = 0 Mesh stats     points:          197952     faces:            517087     internal faces:  471701     cells:            159954     boundary patches: 11     point zones:      0     face zones:      0     cell zones:      2 Overall number of cells of each type:     hexahedra:    136530     prisms:        0     wedges:        0     pyramids:      0     tet wedges:    0     tetrahedra:    0     polyhedra:    23424 Checking topology...     Boundary definition OK.     Point usage OK.     Upper triangular ordering OK.     Face vertices OK.     Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces ...     Patch              Faces    Points  Surface topology                      Inlet              289      324      ok (non-closed singly connected)      Outlet              289      324      ok (non-closed singly connected)      minY1              2074    2259    ok (non-closed singly connected)      maxY1              2074    2259    ok (non-closed singly connected)      minZ1              2074    2259    ok (non-closed singly connected)      maxZ1              2074    2259    ok (non-closed singly connected)      minY2              2074    2259    ok (non-closed singly connected)      maxY2              2074    2259    ok (non-closed singly connected)      minZ2              2074    2259    ok (non-closed singly connected)      maxZ2              2074    2259    ok (non-closed singly connected)      Air_to_Solid        28216    28752    ok (non-closed singly connected)  Checking geometry...     Overall domain bounding box (-0.275 -0.000425 -0.000425) (0.275 0.000425 0.000425)     Mesh (non-empty, non-wedge) directions (1 1 1)     Mesh (non-empty) directions (1 1 1)     Boundary openness (2.298745e-20 -7.724642e-16 -7.724659e-16) OK.     Max cell openness = 4.963084e-16 OK.     Max aspect ratio = 160 OK.     Minumum face area = 3.90625e-11. Maximum face area = 2.5e-07.  Face area magnitudes OK.     Min volume = 3.90625e-14. Max volume = 1.25e-11.  Total volume = 3.9325e-07.  Cell volumes OK.     Mesh non-orthogonality Max: 18.43495 average: 5.826624     Non-orthogonality check OK.     Face pyramids OK.     Max skewness = 0.3477894 OK. Mesh OK. End```
I don't know what is wrong :(. Any help is appreciated!

CU Tobias

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