[snappyHexMesh] Surface feature dict and layer addition

Hr_kules · March 16, 2023, 06:03

Hi, i have a technicall question for layer addition. So far i know that the extraction of surface features helps with capturing sharper angles in a arbitrary geometry, however when it comes to layer addition i wonder, if the produced eMeshes are also used.

I noticed that snappyHexMesh has also problems with creating nice layer, if the geometry has angles like 90 degrees at the boundary.

Maybe someone knows more than me

Yann · March 16, 2023, 10:29

Hello Nico,

AFAIK, snappy don't use eMesh for the layer addition.

Dealing with layers in snappy is pretty tricky, and it usually struggles to create layers due to mesh quality criteria (some layers are not created because snappy cannot find a way to create those layers while respecting quality criteria)

Having a uniform cell level over the surface usually helps to avoid missing layers at cell level transitions but sharp angles are always difficult, if not impossible to mesh properly.

If you are using the ESI-OpenCFD branch, they introduced multi pass layer addition in OpenFOAM-v2206 (https://www.openfoam.com/news/main-n...hexmesh-layers)
I've been able to improve layer addition with this feature but it can increase the meshing time by a lot depending on how many layers you want to add.

Regards,
Yann

Hr_kules · March 16, 2023, 15:36

Hi Yann,

Nice to hear from you again. To be honest, i do the base mesh in gmsh; after a while snappy and i didn't became friends. Gmsh doesn't Support layer addition properly. For the application i am working on gmsh has a lot of advantages. The layers can be added with snappy after importing but Problems with 90 degree angles persist. The Problems are pretty similar to meshing with snappy itself. Since edge Meshes help quite good, i thought it would also help with layers. But i guess i need to find another solution

Thanks anyways!

March 16, 2023, 06:03	Surface feature dict and layer addition	#1
Hr_kules Senior Member Nico Join Date: Jan 2022 Location: Germany Posts: 122 Rep Power: 6	Hi, i have a technicall question for layer addition. So far i know that the extraction of surface features helps with capturing sharper angles in a arbitrary geometry, however when it comes to layer addition i wonder, if the produced eMeshes are also used. I noticed that snappyHexMesh has also problems with creating nice layer, if the geometry has angles like 90 degrees at the boundary. Maybe someone knows more than me

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March 16, 2023, 10:29		#2
Yann Senior Member Yann Join Date: Apr 2012 Location: France Posts: 1,170 Rep Power: 27	Hello Nico, AFAIK, snappy don't use eMesh for the layer addition. Dealing with layers in snappy is pretty tricky, and it usually struggles to create layers due to mesh quality criteria (some layers are not created because snappy cannot find a way to create those layers while respecting quality criteria) Having a uniform cell level over the surface usually helps to avoid missing layers at cell level transitions but sharp angles are always difficult, if not impossible to mesh properly. If you are using the ESI-OpenCFD branch, they introduced multi pass layer addition in OpenFOAM-v2206 (https://www.openfoam.com/news/main-n...hexmesh-layers) I've been able to improve layer addition with this feature but it can increase the meshing time by a lot depending on how many layers you want to add. Regards, Yann

March 16, 2023, 15:36		#3
Hr_kules Senior Member Nico Join Date: Jan 2022 Location: Germany Posts: 122 Rep Power: 6	Hi Yann, Nice to hear from you again. To be honest, i do the base mesh in gmsh; after a while snappy and i didn't became friends. Gmsh doesn't Support layer addition properly. For the application i am working on gmsh has a lot of advantages. The layers can be added with snappy after importing but Problems with 90 degree angles persist. The Problems are pretty similar to meshing with snappy itself. Since edge Meshes help quite good, i thought it would also help with layers. But i guess i need to find another solution Thanks anyways!