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Steps in Mesh by SnappyHexMesh

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Old   September 3, 2019, 02:31
Default Steps in Mesh by SnappyHexMesh
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chandra shekhar pant
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Hello All,


I am trying to simulate the blunt edge aerofoil with a slot at a distance of 60% chord length. I had created the stl file in gmsh and imported the stl into the snappyHexMesh. The mesh around the aerofoil looks steppy (in stairs, steep). The screen shot is attached herewith. I tried to check the stl file by using checkSurfaceMesh and it shows ok.
Complete report of the checkSurfaceMesh, snappyHexMesh, surfaceHexMesh dic along with the screenshot of mesh is attached.

Any help is highly welcomed.
Thanks!
Also snappyHexMesh gives this warning: Checking faces in error :
non-orthogonality > 65 degrees : 111012
faces with face pyramid volume < 1e-20 : 0
faces with face-decomposition tet quality < 1e-30 : 1
faces with concavity > 80 degrees : 827
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.02 : 2
faces on cells with determinant < 0.001 : 14
Finished meshing with 111856 illegal faces (concave, zero area or negative cell pyramid volume)
Attached Images
File Type: png aerofoil_mesh.png (70.0 KB, 19 views)
Attached Files
File Type: txt checksurfacemesh.txt (1.6 KB, 2 views)
File Type: c snappyHexMeshDict.c (9.9 KB, 1 views)
File Type: zip log.snappyHexMesh.c.zip (17.5 KB, 0 views)
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Old   September 3, 2019, 03:32
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Philipp Conen
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Hey,

I hope I understand your question in the right way.
If you want to get away the "stairs" you can try to turn
Code:
nCellsBetweenLevels 1;
into
Code:
nCellsBetweenLevels 2;
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Old   September 3, 2019, 03:38
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Hello Philipp Cone,



Many thanks for your reply, I will implement and update the results. Thanks again for the prompt and useful reply.
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Old   September 3, 2019, 06:03
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It haven't helped a lot. Please check the updated snap-shot herewith. I am just wondering if this issue may have been due to the meshing while creating the stl file in gmsh? Although not sure, if this is the issue of snappyHex or problem with the stl/gmsh. Any help or comment is highly welcomed.


Thanks!
Attached Images
File Type: png aerofoil_changed.png (92.9 KB, 12 views)
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Old   September 3, 2019, 07:12
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Hey,

sorry I am really new to OpenFOAM.
Maybe this can help.
Can you tell me why you use
Code:
resolveFeatureAngle -1;
?
I never saw a negativ value for this.
I would try out
Code:
resolveFeatureAngle 30;
But remember to change the surfaceFeaturesDict and the surfaceFeaturesExtractDict.
With a value of 30 you have to use
Code:
 includedAngle   150;
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Old   September 4, 2019, 02:03
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Hello,

Thanks for your valuable inputs. I tried to changed whatever you have suggested like, changing the nCellsBetweenLevels, resolveFeatureAngle to 2 and 30 respectively. Also change the surfaceFeatureExtract dir. according to your inputs. The snappyHexMesh dic and the surfaceFeatureExtract dir along with the updated snapshot of the mesh is attached. Is that issue could be from the stl file ? The stl file is attached also herewith.



Again thanks for the help would highly appreciate any further inputs.


Thanks!
Attached Images
File Type: png aerofoil_mesh_modifiedv1.png (64.4 KB, 10 views)
Attached Files
File Type: c snappyHexMeshDict.c (10.1 KB, 0 views)
File Type: c surfaceFeatureExtractDict.c (1.3 KB, 0 views)
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Old   September 4, 2019, 02:12
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Hey,

of course, it could also be due to the STL. As already mentioned, I'm not a professional yet.
Unfortunately I have no experience with GMSH. I can only recommend the use of Salome. With it very solid surface nets can be created. For the meshing I recommend Mefisto for 2D. Under 1D you can choose Wire Distance. In a box next to it you can choose a local length of 0.002m for example. That depends on your component size.
Otherwise, I can't think of another quick tip for you. I am sorry.
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Old   September 4, 2019, 02:25
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Hello,
I am truly very happy and thankful with your inputs. These inputs have really helped me, I will try to switch these software. Thanks again!
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Old   September 5, 2019, 02:15
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Hey,

your welcome.
Fell free to ask further questions!
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