[snappyHexMesh] SnappyHexMesh creates extra patch on a multi-region problem

giorgianig · June 13, 2025, 06:05

Dear all,

I am running a multiregion case with 7 regions, nested one inside the other. The most inner region is called Piege. I am struggling to obtain a valid mesh as snappyHexMesh generates an extra patch with very few faces called Piege as it were an external surface. Here is part of the checkMesh output:

HTML Code:

Checking patch topology for multiply connected surfaces... 
Patch    Faces   Points  Surface topology
Cont_ext_bot    84036    85201  ok (non-closed singly connected)
Cont_ext_lat   400200   403913  ok (non-closed singly connected)
Cont_ext_top    84036    85201  ok (non-closed singly connected)
Piege        2        4      ok (closed singly connected)
".*"   568274   571991      ok (closed singly connected)

The other three patch "Cont_ext_blabla" are correct, they are the external surfaces of the most external region.

I managed to visualize this Piege patch in Paraview and it is composed by two very small faces. The mesh is of very good quality.

Does anyone ever had a similar behaviour?

Thanks in advance.

giorgianig · June 13, 2025, 06:41

Additional info, between the .stl that I use to define the geometry there's one called Piege. I have seen that at the beginning snappyHexMesh generate a patch for each .stl, so I guess the internal ones used to define the boundaries between regions are collapsed during the mesh computation as internal faces. So probably for some reason a couple of faces of the patch Piege are not collapsed.
No idea why though.
Maybe I can force the collapsing of these two extra faces?

June 13, 2025, 06:05	SnappyHexMesh creates extra patch on a multi-region problem	#1
giorgianig Member Giorgio Join Date: Mar 2023 Posts: 79 Rep Power: 4	Dear all, I am running a multiregion case with 7 regions, nested one inside the other. The most inner region is called Piege. I am struggling to obtain a valid mesh as snappyHexMesh generates an extra patch with very few faces called Piege as it were an external surface. Here is part of the checkMesh output: HTML Code: Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology Cont_ext_bot 84036 85201 ok (non-closed singly connected) Cont_ext_lat 400200 403913 ok (non-closed singly connected) Cont_ext_top 84036 85201 ok (non-closed singly connected) Piege 2 4 ok (closed singly connected) ".*" 568274 571991 ok (closed singly connected) The other three patch "Cont_ext_blabla" are correct, they are the external surfaces of the most external region. I managed to visualize this Piege patch in Paraview and it is composed by two very small faces. The mesh is of very good quality. Does anyone ever had a similar behaviour? Thanks in advance.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
How to adress boundary patch from another region in chtMultiRegionFoam?	Aniy	OpenFOAM Programming & Development	1	October 7, 2021 07:56
Problem with chtMultiregionFoam radiation boundary condition	baran_foam	OpenFOAM Running, Solving & CFD	10	December 17, 2019 17:36
[snappyHexMesh] SnappyHexMesh Patch Problem	Perschr	OpenFOAM Meshing & Mesh Conversion	0	October 8, 2016 12:09
[snappyHexMesh] Multi region meshing with SHM creates extra regions	Dav3dum	OpenFOAM Meshing & Mesh Conversion	0	August 8, 2016 08:54
Multicomponent fluid	Andrea	CFX	2	October 11, 2004 05:12

June 13, 2025, 06:41		#2
giorgianig Member Giorgio Join Date: Mar 2023 Posts: 79 Rep Power: 4	Additional info, between the .stl that I use to define the geometry there's one called Piege. I have seen that at the beginning snappyHexMesh generate a patch for each .stl, so I guess the internal ones used to define the boundaries between regions are collapsed during the mesh computation as internal faces. So probably for some reason a couple of faces of the patch Piege are not collapsed. No idea why though. Maybe I can force the collapsing of these two extra faces?