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[CAD formats] STL file meshing, refinement, BCs

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Old   July 20, 2015, 12:18
Question STL file meshing, refinement, BCs
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Greetings all,

I've been looking into using OpenFOAM for CFD simulation for a little over half a year now and have been slowly learning the setup for cases and simulations. Unfortunately I'm still a bit lost on how to take a model I've created and perform a simulation on it, or how to mesh it correctly.

As it stands, I have an STL file of a 3-D half-wing, created in CATIA V5, and a working installation of OpenFOAM (ran tutorial cases). I've tried using GmsH and enGrid to produce a mesh + boundary conditions but I cannot finish a mesh, to say the least.

EnGrid typically mangles my model, producing a noisy version of the wing where the top and bottom surfaces intersect randomly. Even if I can set boundary conditions, the geometry is useless as such. GmsH on the other hand I cannot figure out how to set boundary conditions nor do I know how to refine the mesh to be something other than the subdivision of the original mesh.

Furthermore, as related to boundary conditions, I do not know whether I should be adding "patches" in CATIA for a 'wind tunnel' or if I should simply model the wing alone and add patches in the meshing program.

tl;dr I have a CATIA STL file I need to mesh and simulate in OpenFOAM and I don't know where to start.
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Old   August 3, 2015, 08:15
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Hello,

I had pretty much the same questions, so don't worry. When you mesh a wing with enGrid, you have to make sure the upper and lower part of the wing are patched separately. Therefore you can use the stl you created in CATIA and patch it with Blender. How? -> https://github.com/enGits/engrid/wik...and-enGrid-1.2
Working with stl in gmsh isn't easy, I haven't figured it out completely yet. You can set boundary codes with physical entities.

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Furthermore, as related to boundary conditions, I do not know whether I should be adding "patches" in CATIA for a 'wind tunnel' or if I should simply model the wing alone and add patches in the meshing program
Either is possible. I prefer to create the wind tunnel in Blender or gmsh.

Best regards,

Kate
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Old   August 16, 2015, 18:48
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The problem I'm having is more or less that I'm not sure how to name patches, walls, etc. from an STL geometry. Every time I port it into gmsh I can't select anything specific to add to a physical group, it's all or nothing. enGrid can separate and name the surfaces fine but it can never create a volume mesh. I'm still not sure if I should be trying to mesh the airfoil + the tunnel or if I should mesh the airfoil and add patches some other way.

I managed to get a box + airfoil meshed with the combination of blockmeshdict and snappyhexmesh, but the airfoil is inserted after time 0, and I'm fairly certain I'm not getting any results because there's no volume mesh to carry U over the airfoil

As it stands my STL looks something like this:

...with the airfoil surrounded by a box with a wall of symmetry at its root. I can change refinement levels fairly easily, whether in CATIA, gmsh, or enGrid, I just cannot for the life of me name boundaries.

At the very least, I can see a volume mesh exists in some way shape or form through gmsh. Whether it makes it to OpenFOAM I have no clue.


Beautiful I know
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