[akarimi]

Hi,

Based on a shell-and-tube heat exchanger example given in the tutorials of OpenFOAM v8 (Foundations version), I tried to generate a mesh for a slightly different heat exchanger using snappyHexMesh. First, I generated the STL files for my heat exchanger in Salome similar to those STL files given in the tutorial. Then I edited the blockMeshDict and snappyHexMeshDict files accordingly. However, when I try to generate the mesh using snappy I get a large number of non-orthogonal elements and lots of warnings about not being able to find a surface near to some points and at the end, it's unable to generate the appropriate mesh. I tried with different number of cells in blockMeshDict and with different locationInMesh in snappyHexMeshDict, but the result didn't change. Considering the similarity of my case and its geometry and physics with the case given in the tutorial, I really wonder what could be the issue. Attached, you may find the case files. I'd really appreciate it if you could help me to resolve the problem.

Regards,
Ali

[oryx]

Your STL files are not "waterproofed".

I opened the STL files in ParaView, and as you can see in the attachments, you have many non-connected edges and areas with ugly looking triangulation. with such bad STLs, snappyHexMesh will have a hard time snapping to the feature edges of your geometry.

What I suggest is:

1. Perform a better surface triangulation (maybe using SALOME) (bonus: follow Tobias Holzmann's tutorials, he addresses this issue deeply).
2. use surfaceFeatureExtract to have a better snapping to the surface

[oryx]

Your goal is to have surface triangulation looking pretty much like this

[akarimi]

Thanks a lot for your help. I tried to follow your recommendations in every step. I also watched Tobias tutorials on Youtube. After that, using Salome, I generated a vey fine triangulated STL files (please see the files in the following link). Then I created a background mesh using blockMesh and finally I applied snappy to create the castellated mesh. But even before snapping and in the process of generating the castellated mesh, always I get a pretty large number of non-orthogonal cells. I tried to increase the level of refinement (through the level parameter), but it just increased the number of non-orthogonal cells. Also, I used the surfaceFeatureExtract and embedded them in the snappy process, however, it didn't make much difference. I'm wondering if I'm missing something here and I'd really appreciate it if you could give me some advice. Thanks.

https://www.dropbox.com/s/ogyx8o327x3tui9/HX.zip?dl=0