[Sam Phillips]

Hi,

I am currently working on a CFD project looking at modelling the flow within a S-Duct diffuser using OpenFOAM. The S-Duct mesh was provided for me in Pointwise and I have subsequently exported this to OpenFOAM. However, when I run the checkMesh command I get the following error messages being produced:

Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
points: 5766480
faces: 22919991
internal faces: 22710632
cells: 8843541
faces per cell: 5.159768355
boundary patches: 4
point zones: 0
face zones: 2
cell zones: 2

Overall number of cells of each type:
hexahedra: 4761700
prisms: 654250
wedges: 0
pyramids: 78809
tet wedges: 0
tetrahedra: 3348782
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 5829 4883 ok (non-closed singly connected)
Outlet 19434 15400 ok (non-closed singly connected)
Symmetry 42003 25108 ok (non-closed singly connected)
Wall 142093 142626 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-630.7356569 -436.5005658 -5.558875756e-14) (203.2 169.4994342 302.6111017)
Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
Mesh has 3 solution (non-empty) directions (1 1 1)
Boundary openness (-9.72856767e-16 -1.002082513e-16 -2.857681002e-16) OK.
***High aspect ratio cells found, Max aspect ratio: 14331.92242, number of cells 164430
<<Writing 164430 cells with high aspect ratio to set highAspectRatioCells
Minimum face area = 0.0002272906038. Maximum face area = 783.1700631. Face area magnitudes OK.
Min volume = 5.320976163e-05. Max volume = 6837.581389. Total volume = 30214619.72. Cell volumes OK.
Mesh non-orthogonality Max: 89.39297691 average: 12.37164269
*Number of severely non-orthogonal (> 70 degrees) faces: 1129.
Non-orthogonality check OK.
<<Writing 1129 non-orthogonal faces to set nonOrthoFaces
***Error in face pyramids: 30 faces are incorrectly oriented.
<<Writing 30 faces with incorrect orientation to set wrongOrientedFaces
Max skewness = 0.8685866107 OK.
Coupled point location match (average 0) OK.

Failed 2 mesh checks.

I had anticipated the warning concerning high aspect ratio cells, however I am concerned about the error in face pyramids. I am attempting to run a k-w turbulence model which is currently crashing after about 10 mins of run time. I believe the error in the face pyramids could be the reason why.

Could anyone provide me with any assistance on how to resolve this error, either from within OpenFOAM or in Pointwise? I have looked into changing the orientation of my cells in Pointwise however I am unsure as to how to locate the 30 faces that are causing OpenFOAM problems? Any help would be greatly appreciated.

Many thanks in advance.
Sam

[geth03]

your mesh is really really bad.
your non-orthogonality is nearly 90. convergence is hardly achieved at those numbers, and if so, the results might not be reliable.

in polyMesh, there will be a new folder created, which is called 'set', after you execute checkMesh.
you can visualize those entries with foamToVTK:
foamToVTK -faceSet wrongOrientedFaces
a folder within you case will be created, its called 'VTK'.
drag and drop those files in paraview and you can see your bad mesh.

[Sam Phillips]

Hi geth03,

Thanks for your reply. I have done as you recommended and can now see the bad parts of my mesh in paraview. Could you provide me with any recommendations on how to improve the mesh, in particular the non-orthogonality if this is a big issue for convergence? How would I go about reducing this value.

Many thanks for your help.
Sam

[geth03]

you need to remesh your geometry with pointwise,
i think you can also show mesh quality data on pointwise.
do a google search which key metrics are important and
what values they should have. the most important metrics for openfoam
are aspect ratio, skewness, and non-orthogonality.