[Gmsh] Strange large tetrahedra in transfinite volume

[Ingraham, Daniel J. (GRC-LTV0)]

Hi Gmsh mailing list,

I'm trying to put together a boundary-layer-style mesh[1] for a
Computational Fluid Dynamics simulation using the Transfinite Line,
Surface, and Volume commands. The line and surface meshes look great,
but using the Transfinite Volume command gives me a mesh with a couple
of issues. First, the volume edges don't line up with the surface edges for
a few cells, despite my careful adjustment of the surface mesh
orientation in the call to `Transfinite Surface` (i.e., `Transfinite
Surface{inflow_s} = {} Left;`). I've attached screenshots of the mesh,
one displaying only surface edges (`bl_mesh-no_volume_edges.png`) and
the other showing surface and volume edges
(`bl_mesh-with_volume_edges.png`). You'll see a couple of the elements
look like they have "X" on their faces in the surface+volume edge
picture, indicating the problem.

The second issue: when I clip the mesh in the Gmsh GUI, I see these
apparently random large tetrahedra that appear to be intersecting the
happy-looking small tetrahedra that I intended to create. The screenshot
named `bl_mesh_clip-strange_large_tets.png` shows what I'm talking
about. My guess is that this second problem is causing the first one.

I've attached the .geo files I'm using. Any ideas?

Thanks!

Daniel

[1] Very small mesh spacing normal to the wall that slowly grows in the
wall-normal direction, and a more-or-less uniform spacing tangent to the
wall.

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