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[snappyHexMesh] No layers from snappyHexMesh

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Old   June 18, 2018, 09:45
Default No layers from snappyHexMesh
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Dear fellow Foamers,

I'm still quite new to OpenFOAM and am using snappyHexMesh to mesh to mesh the flow over a small blended wing body.
The results from the first two parts of sHM, being the castellatedMesh and snapping algorithms, are quite fine without many (say less than 5) non-orthogonality or other illegal faces.
However, when I try to add layers I never seem to get any, or way to few (layers << 1).
I've tried playing around with all the parameters from addLayersControls, but nothing seems to work.

my sHMDict:

            nSurfaceLayers 15;

    relativeSizes       false; // false, usually with firstLayerThickness
    expansionRatio      1.5;
    firstLayerThickness 8e-6;
    //finalLayerThickness 0.7;
    minThickness        1e-06;

    minMedianAxisAngle    80;
    //maxThicknessToMedialRatio    0.6;
    //maxFaceThicknessRatio    0.6;

    featureAngle     180;
    nSmoothSurfaceNormals    50;
    nSmoothNormals    50;         
    nSmoothThickness    300;

    nRelaxIter        30;
    nLayerIter         50;
    nRelaxedIter    30;

Perhaps an sHM expert can already see what's going wrong from the above code, but in case you need more info I attached my full sHMDicts and logs as well. The ones with the _coarse extension are on a coarser (1.5E6 instead of 9E6) mesh.

It would therefor be really helpful if somebody with more sHM experience can tell me what I'm doing wrong.
Thanks in advance!

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Old   June 18, 2018, 12:21
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I'm not an sHM expert, but I share my experiences with you, maybe it can help.
First of all, try to add less layers once. Try with 3-5 layers. Then another 3-5 layers, etc...
Also try with relativeSizes true; Usually like this shm can generate more layers.
Try with less and greater layers (ie 1-2 layers with 0.5 relativeSize), which is easier to generate. If it will also fail somewhere, you will know the problematic regions.

Also in OpenFOAM by esi group (ie.: v1712, the latest), you can use a different mesh shrinking algorithm (using displacementLaplacian instead of medialAxis) which works much better at the sharp edges. So if you have it, you could try it.

Or if you are really lost, try cfMesh. It can generate the BL with 100% coverage and it is really simple to use, and it can generate a really nice mesh. (Also included in v1712, but you can download it for v5.0 too.)
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Old   June 25, 2018, 05:36
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Hey Simrego,

Thanks for the fast reply! Sorry I didn't respond sooner, I overlooked my mailbox.
I'll definitely have a try at this quite soon and will let you know how it goes.
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