[woodie]

Good day all,

My problem is related to Ansys ICEM, the conversion to OpenFOAM and checkMesh errors.

I have made a hexahedral mesh in ICEM CFD 18.1 (single wind turbine rotor blade, see. Fig.1/2) with about 7M cells.

After conversion too OpenFOAM (fluent3DMeshToFoam) everything seems fine, checkMesh -allTopology gives the following output though:

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create mesh for time = 0

Enabling all (cell, face, edge, point) topology checks.

Enabling all geometry checks.

Time = 0

Mesh stats
    points:           7067496
    faces:            20959026
    internal faces:   20715676
    cells:            6945947
    faces per cell:   5.99985891
    boundary patches: 7
    point zones:      0
    face zones:       1
    cell zones:       1

Overall number of cells of each type:
    hexahedra:     6944967
    prisms:        980
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     0

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Topological cell zip-up check OK.
    Face-face connectivity OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
    Patch               Faces    Points   Surface topology                   Bounding box
    BLADE               36744    36839    ok (non-closed singly connected)   (-1.80496822 -0.944902034 1.47313936) (0.982712077 0.944827568 35.01)
    INLET               32929    33300    ok (non-closed singly connected)   (-103.92305 -90 0.875) (103.92305 -90 119.998012)
    HUB                 31215    31643    ok (non-closed singly connected)   (-1.51554446 -90 0.875) (1.51554446 350 1.74999999)
    OUTLET              32929    33300    ok (non-closed singly connected)   (-207.8461 350 0.875) (207.8461 350 239.99482)
    SIDE_LEFT           44421    44844    ok (non-closed singly connected)   (-207.8461 -90 0.875) (-1.51554441 350 120)
    SIDE_RIGHT          32929    33300    ok (non-closed singly connected)   (1.51554441 -90 0.875) (207.8461 350 120)
    TOP                 32183    32498    ok (non-closed singly connected)   (-207.8461 -90 60) (207.8461 350 239.99482)

Checking faceZone topology for multiply connected surfaces...
    FaceZone            Faces    Points   Surface topology                   Bounding box
    int_FLUID           20715676 7067488  multiply connected (shared edge)   (-206.631866 -90 0.875) (206.655689 350 239.99482)
  <<Writing 7065113 conflicting points to set nonManifoldPoints

Checking basic cellZone addressing...
    CellZone            Cells        Points       Volume       BoundingBox
    FLUID               6945947      7067496      15472908.6   (-207.8461 -90 0.875) (207.8461 350 239.99482)

Checking geometry...
    Overall domain bounding box (-207.8461 -90 0.875) (207.8461 350 239.99482)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (8.53833983e-17 -5.91260289e-16 6.12398899e-16) OK.
 ***High aspect ratio cells found, Max aspect ratio: 15610.2635, number of cells 4324
  <<Writing 4324 cells with high aspect ratio to set highAspectRatioCells
    Minimum face area = 1.96668796e-09. Maximum face area = 209.596829.  Face area magnitudes OK.
    Min volume = 4.13112397e-12. Max volume = 1052.66242.  Total volume = 15472908.6.  Cell volumes OK.
    Mesh non-orthogonality Max: 89.825889 average: 18.8627287
   *Number of severely non-orthogonal (> 70 degrees) faces: 15644.
    Non-orthogonality check OK.
  <<Writing 15644 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
    Max skewness = 3.18585766 OK.
    Coupled point location match (average 0) OK.
 ***Error in face tets: 106564 faces with low quality or negative volume decomposition tets.
  <<Writing 106564 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces
   *Edges too small, min/max edge length = 2.34169721e-06 21.8345617, number too small: 837655
  <<Writing 837655 points on short edges to set shortEdges
  <<Writing 837657 near (closer than 0.000650828928 apart) points to set nearPoints
   *There are 6 faces with concave angles between consecutive edges. Max concave angle = 89.3707312 degrees.
  <<Writing 6 faces with concave angles to set concaveFaces
    Face flatness (1 = flat, 0 = butterfly) : min = 0.612468465  average = 0.999992307
   *There are 8 faces with ratio between projected and actual area < 0.8
    Minimum ratio (minimum flatness, maximum warpage) = 0.612468465
  <<Writing 8 warped faces to set warpedFaces
    Cell determinant (wellposedness) : minimum: 5.08273978e-15 average: 0.0490945013
 ***Cells with small determinant (< 0.001) found, number of cells: 2334747
  <<Writing 2334747 under-determined cells to set underdeterminedCells
    Concave cell check OK.
    Face interpolation weight : minimum: 0.000349430852 average: 0.479246783
 ***Faces with small interpolation weight (< 0.05) found, number of faces: 5365
  <<Writing 5365 faces with low interpolation weights to set lowWeightFaces
    Face volume ratio : minimum: 0.000318593433 average: 0.913266952
 ***Faces with small volume ratio (< 0.01) found, number of faces: 2448
  <<Writing 2448 faces with low volume ratio cells to set lowVolRatioFaces

Failed 5 mesh checks.

End

Yes, orthogonality and aspect ratio are not good - but i am more interested in the rest of the errors. In particular this one:

***Error in face tets: 106564 faces with low quality or negative volume decomposition tets.

The reason being that it creates problems with mapFields, while the simulation is running without problems.
The faceSet lowQualityTetFaces is visualised in Figures 3/4 (most of the faces are on the blade surfaces), i dont understand why there would be Tet-Faces since they should be hex.
Why is OpenFOAM even decomposing into tets?



Does anyone have an idea why this error occurs? Something must have happend converting the mesh.

ICEM: Mesh Check finds some penetrating and overlapping elements (it doesnt seem like they are the cause for this), all cell determinants are above 0.1, Quality for 99.96% of elements above 0.4.

using OpenFOAM-v1912
any help is much appreciated, if more info is needed - let me know!

best regards
christoph

[hjasak]

Hi,

Yet decomposition is done because this is how you calculate the cell volume and cell centre for a polyhedron. It means that some of the faces are ciccave, but I’d like to see precisely how.

Can I have a look at this mesh? You can contact me on h.jasak at wikki.co.uk

Hrv

[woodie]

Thanks for your quick response. Of course you can have a look, i have already messaged you.

Christoph

[hjasak]

Not received - can you try again please?

[Sakun]

hi guys,

any recommendation for this issue ? because i am having the same

many thanks