[Gmsh] Problem with meshing a ridge with an extrusion of 20 mm

[look]

Dear gmsh community,

Currently I am working on a part of an airfoil which has a ridge of 5 mm on the trailing edge. Please see the attached screenshot. I mesh the surface in enGrid and lateron I create an extrusion on that surface of an absolute height of 20 mm. On that extrusion I build a volume tet mesh with gmsh. 

I finally got it to work but after I converted the mesh to OpenFOAM with gmshToFoam, checkMesh complain about some bad quality cells. Please see the following output:

<CODE>
Kates-MacBook-Pro:geometry kate$ checkMesh
/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
Build  : 2.3.1-262087cdf8db
Exec   : checkMesh
Date   : Jul 23 2015
Time   : 16:58:31
Host   : "Kates-MacBook-Pro.local"
PID    : 70687
Case   : /Users/kateeisenhower/Documents/gmsh/Data/geometry
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Allowing user-supplied system call operations

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

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:           680409
    faces:            5884664
    internal faces:   5515361
    cells:            2760292
    faces per cell:   4.13001
    boundary patches: 2
    point zones:      0
    face zones:       1
    cell zones:       1

Overall number of cells of each type:
    hexahedra:     0
    prisms:        358857
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    2401435
    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                  
    patch0              368444   184719   ok (non-closed singly connected)  
    defaultFaces        859      754      multiply connected (shared edge)  
  <<Writing 286 conflicting points to set nonManifoldPoints

Checking geometry...
    Overall domain bounding box (-3 -0.501511 -3) (3 0.501988 3)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (1.30587e-19 2.76155e-16 2.35201e-16) OK.
    Max cell openness = 5.12735e-16 OK.
    Max aspect ratio = 45.2301 OK.
    Minimum face area = 1.53274e-09. Maximum face area = 0.566488.  Face area magnitudes OK.
    Min volume = 1.13287e-09. Max volume = 0.102629.  Total volume = 35.889.  Cell volumes OK.
    Mesh non-orthogonality Max: 178.031 average: 14.488
   *Number of severely non-orthogonal (> 70 degrees) faces: 384.
 ***Number of non-orthogonality errors: 26.
  <<Writing 410 non-orthogonal faces to set nonOrthoFaces
 ***Error in face pyramids: 307 faces are incorrectly oriented.
  <<Writing 304 faces with incorrect orientation to set wrongOrientedFaces
 ***Max skewness = 211.421, 8 highly skew faces detected which may impair the quality of the results
  <<Writing 8 skew faces to set skewFaces
    Coupled point location match (average 0) OK.

Failed 3 mesh checks.

End

</CODE>

Especially the 286 conflicting points (nonManifoldPoints), the non-orthogonal faces and the faces with incorrect orientation bother me. I checked the problematic faces in ParaView and the problematic cells are all in the area around the ridge. However I didn’t know how to locate the nonManifoldPoints but I guess they are also located in this place.
I think there are a few possible solutions now:

1) Make one sharp edge instead of the two edges which form the trailing edge
2) Mesh the ridge surface mesh with smaller elements
3) Mesh the ridge surface mesh with bigger elements
4) Make a a radius instead of a ridge

All of these options would be okay for me. Which method would you recommend for meshing a trailing edge? And which element size would you recommend?

If someone has any other idea I would be very grateful if you could share it. How is this kind of problem handled usually?

Best regards and thanks in advance,

Kate

P.S.: If you need any further information please don’t hesitate to ask!
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