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Convergence blues

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Old   June 26, 2019, 13:31
Default Convergence blues
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Joe
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Hi,


Im running a simpleFoam case with k-e. After approximately 570 iterations the simulation crashes. Any general ideas on what might cause this? Attached the residuals and the instability - the velocity goes through the roof..


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File Type: png Residuals.png (39.1 KB, 25 views)
File Type: png V1.png (33.0 KB, 23 views)
File Type: png V2.png (20.8 KB, 19 views)
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Old   June 27, 2019, 05:19
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Does checkMesh complain about the mesh quality?
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Old   June 28, 2019, 18:00
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Hi jherb,


I think the mesh is ok.. see below:


Mesh stats
points: 171587
faces: 1781432
internal faces: 1682136
cells: 865892
faces per cell: 4
boundary patches: 7
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 0
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 865892
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
inlet1 238 141 ok (non-closed singly connected)
inlet2 232 138 ok (non-closed singly connected)
outlet1 232 138 ok (non-closed singly connected)
outlet2 234 139 ok (non-closed singly connected)
sym 36380 18443 ok (non-closed singly connected)
wall1 48840 24753 ok (non-closed singly connected)
pipes 13140 6738 ok (non-closed singly connected)

Checking faceZone topology for multiply connected surfaces...
No faceZones found.

Checking basic cellZone addressing...
No cellZones found.

Checking geometry...
Overall domain bounding box (0 0 0) (194 189 13)
Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
Mesh has 3 solution (non-empty) directions (1 1 1)
Boundary openness (-1.05596e-16 6.78774e-18 3.33865e-15) OK.
Max cell openness = 2.51381e-16 OK.
Max aspect ratio = 6.12287 OK.
Minimum face area = 0.00594874. Maximum face area = 4.18215. Face area magnitudes OK.
Min volume = 0.000219401. Max volume = 2.55495. Total volume = 464436. Cell volumes OK.
Mesh non-orthogonality Max: 52.7944 average: 14.6586
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 0.688954 OK.
Coupled point location match (average 0) OK.

Mesh OK.

End
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Old   June 29, 2019, 07:11
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Ok. Step by step. What are the settings in fvSchemes and fvSolutions?
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Old   July 1, 2019, 15:36
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Hi jherb...thanks for the reply.. attached the settings:
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File Type: png fvsolution.png (38.0 KB, 9 views)
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Old   July 1, 2019, 18:25
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Ok, just guesses: You could try to increase the nNonOrthogonalCorrectors to something like 2 or 3 and reduce the relaxation factors.
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Old   July 2, 2019, 06:34
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It works when I reduce the k,e & U relaxation to 0.2 at the start of the simulation then gradually increase to 0.5. The 0.2 seems a bit low but the results are looking ok I think.
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high velocity, residuals, simplefoam, unstable

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