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JR22 February 25, 2013 09:28

Best way to create inlet/outlet out of STL files?

I am fairly new to OpenFoam (I am an ex-Comsol refugee). I am trying to use one of the pre-processing/meshing packages (Helyx-OS, Engrid, etc.) to model the internal flow of a contraption for which I have a surface file (STL). My problem is that I can't find a way of defining the inlet and outlet faces (boundaries) using such software. This has to be a common initial problem for beginners.

I have been trying to use a single STL of the whole contraption. Is there a surface-mesh format to use better than STL that allows definition of what faces are? I have been able to use Helyx-OS successfully to create a wind-tunnel type simulation. But this more basic one, purportedly simpler, is becoming kind of a pain.

Thank you very much,


JR22 February 26, 2013 00:49

I got it to work. This is what I did:

Using a combination of FreeCAD and MeshLab (both open source):
1. I erased the outlet faces from the STL and created a new STL with only the outlet faces. The STLs were aligned so that when I call both, the lid (outlet) falls in place. I didn't care for the inlet because I just cut the tube in the next step.
Using Helyx-OS (uses SnappyHexMesh):
2. I uploaded both STLs (body, outlet) as surfaces (not volumes).
3. I created a bounding box. Since one of the sides of the bounding box is orthogonal to the inlet tube, I just made the box small enough so it cut it. Set up my refining levels for boths surfaces. Nothing else used refinement.
4. In the last step of meshing I put the "material point" coordinate in a place where the flow will exist (within the contraption)
5. Ran the meshing
6. Reloaded the model
7. Went to the "Case Setup", and set my boundary conditions and parameters as in the youtube tutorial (
After you get the results use within your run directory:
reconstructParMesh -constant followed by

I've seen in this forum a blender script to create named STLs, however, i am not a blender user. Is there a readable mesh file that SnappyHexMesh can access which can contain names?

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