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Old   May 27, 2016, 13:17
Default MRF solving issues
  #1
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carno
Join Date: Mar 2009
Posts: 70
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Hi, I am new to openFOAM. Excuse me if I do any mistake.

I am trying to solve a MRF problem as below. The problem is the run is not able to complete even 10 iterations.
I tried following,
1. Slowly ramping the speed to 3000 rpm
2. Initially tried to solve laminar and switch to turbulence to model k-w and k-e
Nothing seems working.
My problem details are as below.

Meshcheck reports 1 error,

Mesh stats
points: 244533
faces: 2365063
internal faces: 2148809
cells: 1128468
faces per cell: 4
boundary patches: 5
point zones: 0
face zones: 0
cell zones: 3

Overall number of cells of each type:
hexahedra: 0
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 1128468
polyhedra: 0

Checking topology...
Boundary definition OK.
Cell to face addressing 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 854 460 ok (non-closed singly connected)
outlet 1184 630 ok (non-closed singly connected)
walls 18276 9585 ok (non-closed singly connected)
walls_stator 135500 68219 ok (non-closed singly connected)
walls_rotor 60440 30311 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-3.588227 -1.183531 -1.183531) (3.094186 1.183531 1.183531)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-1.01979e-016 -1.406094e-016 -5.540091e-017) OK.
Max cell openness = 3.759495e-016 OK.
Max aspect ratio = 79.51179 OK.
Minimum face area = 1.717113e-007. Maximum face area = 0.02271197. Face area magnitudes OK.
Min volume = 1.808659e-010. Max volume = 0.001020305. Total volume = 23.12361. Cell volumes OK.
Mesh non-orthogonality Max: 87.8478 average: 18.20694
*Number of severely non-orthogonal (> 70 degrees) faces: 389.
Non-orthogonality check OK.
<<Writing 389 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
***Max skewness = 5.490139, 2 highly skew faces detected which may impair the quality of the results
<<Writing 2 skew faces to set skewFaces
Coupled point location match (average 0) OK.

Failed 1 mesh checks.

End
----------------------------------------

Solver exits doing following,

Time = 2

DILUPBiCG: Solving for Ux, Initial residual = 0.3260528, Final residual = 0.0108277, No Iterations 2
DILUPBiCG: Solving for Uy, Initial residual = 0.3300664, Final residual = 0.01127371, No Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 0.3395786, Final residual = 0.01083639, No Iterations 2
GAMG: Solving for p, Initial residual = 0.08636129, Final residual = 0.004401122, No Iterations 7
GAMG: Solving for p, Initial residual = 0.1115448, Final residual = 0.005344135, No Iterations 1
time step continuity errors : sum local = 0.3802423, global = 0.003882829, cumulative = 0.007101267
DILUPBiCG: Solving for epsilon, Initial residual = 0.1713729, Final residual = 0.0156289, No Iterations 1
bounding epsilon, min: -156432.1 max: 3702708 average: 391.6643
DILUPBiCG: Solving for k, Initial residual = 0.4867903, Final residual = 0.04814626, No Iterations 2
ExecutionTime = 32.645 s ClockTime = 32 s

Time = 3

DILUPBiCG: Solving for Ux, Initial residual = 0.4354033, Final residual = 0.02818809, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.7221585, Final residual = 0.05162595, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.4768465, Final residual = 0.04278764, No Iterations 1
GAMG: Solving for p, Initial residual = 0.1660247, Final residual = 0.0114165, No Iterations 2
GAMG: Solving for p, Initial residual = 0.03848046, Final residual = 0.002525837, No Iterations 3
time step continuity errors : sum local = 1.865936e+011, global = 9.781742e+007, cumulative = 9.781742e+007
DILUPBiCG: Solving for epsilon, Initial residual = 1, Final residual = 0.01480226, No Iterations 4
DILUPBiCG: Solving for k, Initial residual = 1, Final residual = 0.07233552, No Iterations 2
ExecutionTime = 46.764 s ClockTime = 46 s

Time = 4

DILUPBiCG: Solving for Ux, Initial residual = 0.6965265, Final residual = 0.02627963, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.6764134, Final residual = 0.03492312, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.8239209, Final residual = 0.0755949, No Iterations 1
GAMG: Solving for p, Initial residual = 0.9999998, Final residual = 6.538528, No Iterations 100
GAMG: Solving for p, Initial residual = 0.0003485187, Final residual = 2.777873e-005, No Iterations 3
time step continuity errors : sum local = 6.827751e+025, global = -3.92473e+023, cumulative = -3.92473e+023
DILUPBiCG: Solving for epsilon, Initial residual = 1, Final residual = 0.05536559, No Iterations 15
DILUPBiCG: Solving for k, Initial residual = 1, Final residual = 0.08238156, No Iterations 3
ExecutionTime = 98.659 s ClockTime = 98 s
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Old   May 27, 2016, 18:00
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  #2
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Arsalan
Join Date: Jul 2014
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Quote:
Originally Posted by Carno View Post

Mesh stats
points: 244533
faces: 2365063
internal faces: 2148809
cells: 1128468
faces per cell: 4
boundary patches: 5
point zones: 0
face zones: 0
cell zones: 3

Overall number of cells of each type:
hexahedra: 0
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 1128468
polyhedra: 0

Checking topology...
Boundary definition OK.
Cell to face addressing 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 854 460 ok (non-closed singly connected)
outlet 1184 630 ok (non-closed singly connected)
walls 18276 9585 ok (non-closed singly connected)
walls_stator 135500 68219 ok (non-closed singly connected)
walls_rotor 60440 30311 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-3.588227 -1.183531 -1.183531) (3.094186 1.183531 1.183531)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-1.01979e-016 -1.406094e-016 -5.540091e-017) OK.
Max cell openness = 3.759495e-016 OK.
Max aspect ratio = 79.51179 OK.
Minimum face area = 1.717113e-007. Maximum face area = 0.02271197. Face area magnitudes OK.
Min volume = 1.808659e-010. Max volume = 0.001020305. Total volume = 23.12361. Cell volumes OK.
Mesh non-orthogonality Max: 87.8478 average: 18.20694
*Number of severely non-orthogonal (> 70 degrees) faces: 389.
Non-orthogonality check OK.
<<Writing 389 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
***Max skewness = 5.490139, 2 highly skew faces detected which may impair the quality of the results
<<Writing 2 skew faces to set skewFaces
Coupled point location match (average 0) OK.

Failed 1 mesh checks.

End
----------------------------------------


Time = 4

DILUPBiCG: Solving for Ux, Initial residual = 0.6965265, Final residual = 0.02627963, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.6764134, Final residual = 0.03492312, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.8239209, Final residual = 0.0755949, No Iterations 1
GAMG: Solving for p, Initial residual = 0.9999998, Final residual = 6.538528, No Iterations 100
GAMG: Solving for p, Initial residual = 0.0003485187, Final residual = 2.777873e-005, No Iterations 3
time step continuity errors : sum local = 6.827751e+025, global = -3.92473e+023, cumulative = -3.92473e+023
DILUPBiCG: Solving for epsilon, Initial residual = 1, Final residual = 0.05536559, No Iterations 15
DILUPBiCG: Solving for k, Initial residual = 1, Final residual = 0.08238156, No Iterations 3
ExecutionTime = 98.659 s ClockTime = 98 s
Hi Carno,

As you said, the checkMesh command report an error from your mesh which is related to max skewness of two cells, and the solver crashes because of high continuity errors (the bold parts of the report) that arise probably from the low quality mesh.

So you can give more details of your problem to get a more accurate help.

Regards,
Arsalan.
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Old   May 30, 2016, 06:54
Default
  #3
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carno
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Posts: 70
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Thanks, Arsalan. I also think it is mesh issue. I will work on it. I used salome for tet-meshing.

I am sending other details also.
The rotor diameter is around 2.2m You might have figured out that from bounding box.
I am using k-w turbulence model.
Inlet: total pressure, Outlet: static pressure
Attaching solver files.

fvSchemes file
Code:
FoamFile
{
version 2.0;
class dictionary;
format ascii;
location "system";
object fvSchemes;
}
ddtSchemes
{
default steadyState;
}
gradSchemes
{
default Gauss linear;
}
divSchemes
{
default bounded Gauss upwind;
div(phi,U) bounded Gauss upwind;
div(phi,k) bounded Gauss upwind;
div(phi,epsilon) bounded Gauss upwind;
div(R) Gauss linear;
div((nuEff*dev(T(grad(U))))) Gauss linear;
}
laplacianSchemes
{
default Gauss linear corrected;
}
interpolationSchemes
{
default linear;
}
snGradSchemes
{
default corrected;
}
fluxRequired
{
default no;
p ;
}

fvSolution file
Code:
FoamFile
{
version 2.0;
class dictionary;
format ascii;
location "system";
object fvSolution;
}
solvers
{
U
{
tolerance 1.0E-6;
preconditioner DILU;
solver PBiCG;
relTol 0.1;
maxIter 100;
}
epsilon
{
tolerance 1.0E-6;
preconditioner DILU;
solver PBiCG;
relTol 0.1;
maxIter 100;
}
omega
{
tolerance 1.0E-6;
preconditioner DILU;
solver PBiCG;
relTol 0.1;
maxIter 100;
}
k
{
tolerance 1.0E-6;
preconditioner DILU;
solver PBiCG;
relTol 0.1;
maxIter 100;
}
p
{
nPostSweeps 1;
solver GAMG;
smoother GaussSeidel;
nFinalSweeps 0;
nPreSweeps 0;
nCellsInCoarsestLevel 100;
cacheAgglomeration true;
maxIter 100;
tolerance 1.0E-6;
agglomerator faceAreaPair;
relTol 0.1;
mergeLevels 1;
}
}
SIMPLE
{
nNonOrthogonalCorrectors 1;
pRefCell 0;
pRefValue 0.0;
residualControl
{
U 1.0E-4;
epsilon 1.0E-4;
k 1.0E-4;
p 1.0E-4;
}
}
relaxationFactors
{
U 0.7;
epsilon 0.8;
k 0.8;
p 0.3;
}
potentialFlow
{
nNonOrthogonalCorrectors 10;
pRefCell 0;
pRefValue 0.0;
}
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