[mactone]

Dear Formers,

I've constructed a burner flowfield geometry. After the blockMesh and snappyHexMesh, the mesh is generated successfully.
I've referenced the post checkMesh Ok but bad cells still present But no solution or explaination in that post. It seems use finer blockMesh is a solution?

My problem is pretty similar to that.

My questions is
1. Will this error has bad influence on my simulation such as bad convergence or bad accuracy due to the errors in the mesh?
2. How to refine the mesh so those errors can go away?
3. Why the checkMesh is okay, but checkMesh with furners options fails?


checkMesh, the output ends as follow, no error was shown:

Checking patch topology for multiply connected surfaces...
                   Patch    Faces   Points                  Surface topology
                     air     4804     5564  ok (non-closed singly connected)
                    fuel     1340     1544  ok (non-closed singly connected)
                  outlet     4104     4613  ok (non-closed singly connected)
             wall_burner    81792    94012  ok (non-closed singly connected)
            wall_chamber   109940   113596  ok (non-closed singly connected)
                   pilot      152      185  ok (non-closed singly connected)

Checking faceZone topology for multiply connected surfaces...
    No faceZones found.

Checking basic cellZone addressing...
    No cellZones found.

Checking geometry...
    Overall domain bounding box (-0.4000000026 -0.4000000026 1.26361801e-08) (0.4000000026 0.4000000026 2.332000017)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-1.120593655e-15 -1.21631218e-15 -7.792938171e-16) OK.
    Max cell openness = 3.319599976e-16 OK.
    Max aspect ratio = 6.429704674 OK.
    Minimum face area = 3.978369824e-08. Maximum face area = 0.0001908707779.  Face area magnitudes OK.
    Min volume = 5.927097015e-11. Max volume = 2.604615265e-06.  Total volume = 0.799458194.  Cell volumes OK.
    Mesh non-orthogonality Max: 54.97320245 average: 7.136477232
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 2.85596137 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

End

But, when I
checkMesh --allTopology --allRegions, the same mesh has errors as follow

Checking faceZone topology for multiply connected surfaces...
    No faceZones found.

Checking basic cellZone addressing...
    No cellZones found.

Checking geometry...
    Overall domain bounding box (-0.4000000026 -0.4000000026 1.26361801e-08) (0.4000000026 0.4000000026 2.332000017)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-1.120593655e-15 -1.21631218e-15 -7.792938171e-16) OK.
    Max cell openness = 3.319599976e-16 OK.
    Max aspect ratio = 6.429704674 OK.
    Minimum face area = 3.978369824e-08. Maximum face area = 0.0001908707779.  Face area magnitudes OK.
    Min volume = 5.927097015e-11. Max volume = 2.604615265e-06.  Total volume = 0.799458194.  Cell volumes OK.
    Mesh non-orthogonality Max: 54.97320245 average: 7.136477232
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 2.85596137 OK.
    Coupled point location match (average 0) OK.
 ***Error in face tets: 344 faces with low quality or negative volume decomposition tets.
  <<Writing 336 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces
    Min/max edge length = 5.657329348e-05 0.01392850623 OK.
   *There are 2166 faces with concave angles between consecutive edges. Max concave angle = 72.7399196 degrees.
  <<Writing 2166 faces with concave angles to set concaveFaces
    Face flatness (1 = flat, 0 = butterfly) : min = 0.4816127466  average = 0.9996852552
   *There are 10 faces with ratio between projected and actual area < 0.8
    Minimum ratio (minimum flatness, maximum warpage) = 0.4816127466
  <<Writing 10 warped faces to set warpedFaces
    Cell determinant (wellposedness) : minimum: 0.01350136115 average: 1.474873198
    Cell determinant check OK.
 ***Concave cells (using face planes) found, number of cells: 38934
  <<Writing 38934 concave cells to set concaveCells
    Face interpolation weight : minimum: 0.1164988534 average: 0.4833431086
    Face interpolation weight check OK.
    Face volume ratio : minimum: 0.02502027251 average: 0.9134506808
    Face volume ratio check OK.

Failed 2 mesh checks.

Writing fields with mesh quality parameters
    Writing non-orthogonality (angle) to nonOrthoAngle
    Writing face interpolation weights (0..0.5) to faceWeight
    Writing face skewness to skewness
    Writing cell determinant to cellDeterminant
    Writing aspect ratio to aspectRatio
    Writing approximate aspect ratio to cellAspectRatio
    Writing cell shape (hex, tet etc.) to cellShapes
    Writing cell volume to cellVolume
    Writing cell volume ratio to cellVolumeRatio
    Writing minTetVolume to minTetVolume
    Writing minPyrVolume to minPyrVolume
    Writing cell region to cellRegion
    Writing cell zoning to cellZone
    Writing face zoning to faceZone

End

Failed 2 mesh checks which are
***Error in face tets: 344 faces with low quality or negative volume decomposition tets.
***Concave cells (using face planes) found, number of cells: 38934

[tomf]

Hi mactone,

My personal experience:

Typically the checkMesh results without additional options should be considered for evaluating if the mesh is of sufficient quality. The additional criteria that are turned on with the options might indicate problems for specific solvers, in particular the Lagrangian solvers, although the past couple of years some work has been devoted on making those more robust as well.

So I would not worry about these 'errors' if they are due to the additional options before running the case.

Best Regards,
Tom

[mactone]

Originally Posted by tomf

Hi mactone,

My personal experience:

Typically the checkMesh results without additional options should be considered for evaluating if the mesh is of sufficient quality. The additional criteria that are turned on with the options might indicate problems for specific solvers, in particular the Lagrangian solvers, although the past couple of years some work has been devoted on making those more robust as well.

So I would not worry about these 'errors' if they are due to the additional options before running the case.

Best Regards,
Tom

Thank you tomf. Good to know the 'errors' from additional options can be not so worried.