[aerospacious]

Hey fellow foamers,


The reason for this post is because I am running into some problems when Extruding a mesh generated by cfMesh.
For some reason the quality of the cfMesh is fine and the checkMesh utility does not flag a single problem.

checkMesh result cfMesh:

Mesh stats
    points:           18141991
    faces:            52760636
    internal faces:   51354113
    cells:            17311300
    faces per cell:   6.01427
    boundary patches: 7
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     17216033
    prisms:        628
    wedges:        0
    pyramids:      1190
    tet wedges:    0
    tetrahedra:    492
    polyhedra:     92957
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            6   13448
            7   14140
            8   108
            9   52169
           12   12980
           15   112

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      486      652  ok (non-closed singly connected)
                  outlet     2008     2288  ok (non-closed singly connected)
                   front   671323   675329  ok (non-closed singly connected)
                    back   684354   688365  ok (non-closed singly connected)
                     top      966     1292  ok (non-closed singly connected)
                  bottom      966     1292  ok (non-closed singly connected)
                  marlyn    46420    47106  ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (-5.3 -0.4 -4) (10.7 -0.299998 4)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (1.74977e-18 3.67367e-13 4.64238e-17) OK.
    Max cell openness = 7.56747e-16 OK.
    Max aspect ratio = 36.5897 OK.
    Minimum face area = 7.09395e-09. Maximum face area = 0.00273625.  Face area magnitudes OK.
    Min volume = 2.33909e-12. Max volume = 0.000108415.  Total volume = 12.7988.  Cell volumes OK.
    Mesh non-orthogonality Max: 61.8058 average: 1.46265
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 1.73461 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

However, when I run extrudeMesh from a patch created by cfMesh it does (not so) funny things.

checkMesh result cfMesh + extrudeMesh:

Mesh stats
    points:           1376730
    internal points:  0
    faces:            2741427
    internal faces:   1371010
    cells:            684354
    faces per cell:   6.00922
    boundary patches: 7
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     677647
    prisms:        224
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     6483
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            7   6429
            8   54

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      162      326  ok (non-closed singly connected)
                  outlet      274      550  ok (non-closed singly connected)
                   front   684354   688365  ok (non-closed singly connected)
                    back   684354   688365  ok (non-closed singly connected)
                     top      322      646  ok (non-closed singly connected)
                  bottom      322      646  ok (non-closed singly connected)
                  marlyn      629     1258  ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (-5.3 -0.3 -4) (10.7 0.700002 4)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-1.40344e-17 1.69986e-13 9.9365e-17) OK.
 ***High aspect ratio cells found, Max aspect ratio: 1.33419e+97, number of cells 7102
  <<Writing 7102 cells with high aspect ratio to set highAspectRatioCells
    Minimum face area = 7.3062e-09. Maximum face area = 0.0529325.  Face area magnitudes OK.
 ***Zero or negative cell volume detected.  Minimum negative volume: -1.7993e-06, Number of negative volume cells: 8
  <<Writing 8 zero volume cells to set zeroVolumeCells
    Mesh non-orthogonality Max: 162.379 average: 1.08717
   *Number of severely non-orthogonal (> 70 degrees) faces: 72.
 ***Number of non-orthogonality errors: 17.
  <<Writing 89 non-orthogonal faces to set nonOrthoFaces
 ***Error in face pyramids: 40 faces are incorrectly oriented.
  <<Writing 35 faces with incorrect orientation to set wrongOrientedFaces
 ***Max skewness = 35.2287, 3 highly skew faces detected which may impair the quality of the results
  <<Writing 3 skew faces to set skewFaces
    Coupled point location match (average 0) OK.

Failed 5 mesh checks.

End

Oddly enough I don think I am doing something weird with the extrudeMeshDict either. Though I encountered some problems before when the merge tolerance was too low resulting in collapsed edges, this is not happening in the current situation.
Furthermore, not all meshes that I have created with cfMesh experienced these kind of problems with extrudeMesh so I am at a loss.


extrudeMeshDict:

constructFrom       patch;

sourceCase          ".";

sourcePatches       (front);
exposedPatchName    back;

flipNormals         false;

nLayers             1;

expansionRatio      1;

extrudeModel        linearNormal;

linearNormalCoeffs
{
    thickness           1;
}

mergeFaces          false;
mergeTol        1e-8;

extrudeMesh log:

Create mesh for time = 0

Selecting extrudeModel linearNormal
Extruding from patch using model linearNormal
Collapsing edges < 1e-08 of bounding box

Extruding patches 1(front) on mesh "/mnt/homedirs/timo.vanpelt/OpenFOAM/timo.vanpelt-5.0/run/cavity/with_cavity/AoA-X/AoA8_r"

Create mesh for time = 0

Adding overall 0 processor patches.
Testing:"/mnt/homedirs/timo.vanpelt/OpenFOAM/timo.vanpelt-5.0/run/cavity/with_cavity/AoA-X/AoA8_r/system/fvSchemes"
Mesh bounding box : (-5.3 -1.4 -4) (10.7 -0.4 4)
        with span : (16 1 8)
Merge distance    : 1e-08

Collapsing edges < 1e-08 ...

            Uncollapsed edges = 0 / 3368633
    Number of points : 1350658
    Not visited      : 0
    Not collapsed    : 1350658
    Collapsed        : 0

Collapsing 0 cells
Writing mesh to "/mnt/homedirs/timo.vanpelt/OpenFOAM/timo.vanpelt-5.0/run/cavity/with_cavity/AoA-X/AoA8_r/constant/region0"
End

Has anyone encountered a similar problem and found a fix, it would be greatly appreciated

[redTo]

Hi Timo,

did you find out, how to improve the mesh quality with cfmesh?