Problem with steadyState solvers using pressure BC

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 December 9, 2009, 09:41 Problem with steadyState solvers using pressure BC #1 New Member   Victor Fleischer Join Date: Nov 2009 Posts: 21 Rep Power: 7 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

December 14, 2009, 06:40
#2
Member

Tobias Holzinger
Join Date: Mar 2009
Location: Munich, Germany
Posts: 46
Rep Power: 8
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         Gauss linear;
}
divSchemes
{
default         Gauss linear;
}
laplacianSchemes
{
default         Gauss linear corrected;
}
interpolationSchemes
{
default         linear;
}

{
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

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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