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blockMesh pipe shape not preserved in bend

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Old   May 22, 2010, 20:07
Default blockMesh pipe shape not preserved in bend
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I am creating different pipe bends in blockMesh, but experience that the shape midway is heavily distorted, that is - not circular. I have looked over the vertices and arc midpoints, but cannot find any major mistakes. Is this a bug? Or should the pipe be created in smalles increments? I believe that this has not been a problem before... I attach a screenshot and blockMeshDict-file.
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File Type: jpg print2_1.jpg (33.7 KB, 126 views)
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File Type: txt blockMeshDict.txt (2.4 KB, 68 views)
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Old   May 24, 2010, 08:30
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... and for the record, the volume specified consists of the circular outlet and inlet only. No other "radial profile shape" is defined. The four arcs connecting inlet and outlet have intersection points with equal distance to the pipe center.

This problem - say bug - is increasingly dominant for higher angles. For a 90 degree bend it is barely visible, but up to 180 degrees it becomes a huge error.

(My geometry also have an internal square shaped volume at centre, to avoid small angles that would else have occured with an radial mesh. This, however, should not affect the entire generated volume.)
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Old   May 25, 2010, 06:42
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blockMesh uses a mapping process which does not conform to surfaces created by compound curves exactly. For arcs upto 90deg the conformance is decent but not exact and above 90deg the conformance is poor.

If you require a mesh that represents your curved pipe exactly you should use an extrusion method, e.g. extrudeMesh.

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Old   May 25, 2010, 07:26
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Henry,

Wouldn't the extrudeMesh be better for single pipe bend studies only? More complex pipe geometries using extruded meshes would have to be stitched together. I assume a setup as illustrated in attached image would be difficult to create using extrudeMesh (this example is generated using blockMesh, but bends with 30-40 degrees increments).
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Last edited by kjetil; May 25, 2010 at 08:13. Reason: typo
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