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[Gmsh] Remove tiny gap between surfaces

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Old   October 2, 2022, 02:17
Default Remove tiny gap between surfaces
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I've a swirler and a conical bluff body whose central rod goes through the swirler. (See image attached below.) The whole setup resides in a cylindrical enclosure creating a burner.

With snappyHexMesh, I receive the warning "The mesh has multiple regions which are not connected by any face .." when I run checkMesh, but no errors. This creates few regions with single cells that, as the warning mentions, are not a part of any face. While the velocity equation is solved without any errors, the pressure correction doesn't even start - crashes in the first time step and first pressure iteration. I suspect the above warning to be the cause. I've been unable to find the solution to resolve the warning. (I've tried refining the mesh, moving the background mesh, enabling minVolCollapseRatio - but to no avail.)

I "learnt" gmsh recently to try and mesh the domain. While I was able to create and export mesh without any errors, one issue exists. There's a tiny gap between bluff body rod and the swirler hole through which the former passes. This gap was ignored by snappyHexMesh, but is deemed meshable by gmsh. I've attached the image below for reference. I want to get rid of this part of the mesh through gmsh "Mesh Options". I cannot modify the geometry.

How can this be done?
Attached Images
File Type: jpg bluff_swirler.jpg (93.2 KB, 4 views)
File Type: jpg mesh.jpg (27.5 KB, 4 views)
File Type: png mesh_zoomed.png (161.9 KB, 4 views)
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Old   October 3, 2022, 13:22
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I'd posted the same question in the Gmsh forum. I was informed reliably by the creator of Gmsh that it isn't possible through Gmsh to remove such gaps. The only solution was to modify the geometry, which I did and solved the problem.

For those interested please follow this link: https://gitlab.onelab.info/gmsh/gmsh/-/issues/2121.
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