[a.aralnu]

I've been trying to run a simulation of flow past a NACA2412 profile. First I made the mesh with ANSYS Fluent but I would always get a bad orthogonality metric and a large aspect ratio, still it should be able to run but all the simulations I run end up crashing.

My mesh is a 3D D-grid with periodic boundaries on the front and back faces of the mesh (along Z direction) in order to simulate the flow over an infinite 3D airfoil.

As someone recommended, I tried using ICEM CFD for the mesh creation and I've done over 5 iterations of the mesh where I get a good mesh quality in ICEM but then, when converting it to openFoam I always end up having a high non orthogonality (around 85).

I always use the renumberMesh command after converting the mesh... and I just noticed that's my problem!!! I just converted my newest mesh and did a checkMesh command and got these metrics.

Overall number of cells of each type:
    hexahedra:     7874145
    prisms:        0
    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.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
    Patch               Faces    Points   Surface topology                  
    outlet              12690    13008    ok (non-closed singly connected)  
    inlet               58327    59616    ok (non-closed singly connected)  
    airfoil             13019    13296    ok (non-closed singly connected)  
    periodic_1          167535   168429   ok (non-closed singly connected)  
    periodic_2          167535   168429   ok (non-closed singly connected)  

Checking geometry...
    Overall domain bounding box (-7.84838 -8 -4.44089e-16) (32.15 8 3)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (3.23885e-16 1.34691e-15 -1.49092e-14) OK.
 ***High aspect ratio cells found, Max aspect ratio: 7145.22, number of cells 673510
  <<Writing 673510 cells with high aspect ratio to set highAspectRatioCells
    Minimum face area = 1.20983e-09. Maximum face area = 0.0639391.  Face area magnitudes OK.
    Min volume = 7.72232e-11. Max volume = 0.00408122.  Total volume = 1837.31.  Cell volumes OK.
    Mesh non-orthogonality Max: 37.1664 average: 6.854
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.228152 OK.
    Coupled point location match (average 4.97604e-09) OK.

After running renumberMesh I get these metrics:

Overall number of cells of each type:
    hexahedra:     7874145
    prisms:        0
    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.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
    Patch               Faces    Points   Surface topology                  
    outlet              12690    13008    ok (non-closed singly connected)  
    inlet               58327    59616    ok (non-closed singly connected)  
    airfoil             13019    13296    ok (non-closed singly connected)  
    periodic_1          167535   168429   ok (non-closed singly connected)  
    periodic_2          167535   168429   ok (non-closed singly connected)  

Checking geometry...
    Overall domain bounding box (-7.84838 -8 -4.44089e-16) (32.15 8 3)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-8.62421e-17 -1.83782e-15 -2.9796e-15) OK.
 ***High aspect ratio cells found, Max aspect ratio: 7174.32, number of cells 673177
  <<Writing 673177 cells with high aspect ratio to set highAspectRatioCells
    Minimum face area = 1.20983e-09. Maximum face area = 0.0639385.  Face area magnitudes OK.
    Min volume = 7.72112e-11. Max volume = 0.00408139.  Total volume = 1837.31.  Cell volumes OK.
    Mesh non-orthogonality Max: 85.4069 average: 7.0512
   *Number of severely non-orthogonal (> 70 degrees) faces: 2810.
    Non-orthogonality check OK.
  <<Writing 2810 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
    Max skewness = 0.228202 OK.
    Coupled point location match (average 5.21154e-09) OK.

I guess that this is the reason why I'm having trouble with what seems to be a perfect mesh in the meshing software...

Does anybody know if there is a way to do renumberMesh without losing mesh quality?

[GerhardHolzinger]

What is the OpenFOAM version you are using?

Have you tried other versions of OpenFOAM?

Do you write the case-files in binary format or with sufficiently high writePrecision?
It is very weird that things like max. volume, max. face area and others change, simply re-ordering the vertices should not alter any of those.

What happens if you change the boundary type of your periodic boundaries to the type patch prior to renumbering and change them back to periodic after renumbering? That's a mere shot into the darkness, although I have never hab problems caused by renumberMesh, I have never really used periodic patches, so I have no idea whether the periodic patches may pose a problem.

[s1291]

I think Gerhard is right about writeFormat. Here is a related issue: https://develop.openfoam.com/Develop.../-/issues/2043

[a.aralnu]

I changed the write format to binary and changed write precision from 6 to 12 and it solved the orthogonality problem! Thank you very much!

I'm still having issues with convergence though. I'm not sure if that's due to my high aspect ratio (my first cell height on airfoil wall is 1.1e-5 so it's pretty hard to fix that) or maybe some mistake with BC's initialization or the fvSchemes... I'll look more into it.

[a.aralnu]

Yeah I found that info a couple hours after posting this and it solved my problem! I just don't know if I can delete this thread or mark it as solved. I'm still having some issues with convergence but I think I should try changing the initial values on my boundaries and tinker with fvSchemes and fvSolution files now that my mesh issue is solved.

Thank you very much for your reply!!