[snappyHexMesh] STL exported from CATIA and snappyHexMesh

ma- · April 9, 2012, 13:02

Hello everyone,

I'm new to openFoam and I'm trying to use snappyHexMesh with a file I exported from CATIA as STL.

I took flange as an example from the tutorials, but it seems that I'm missing something.

1. I put my STL file in the triSurface folder
2. I edited the sHMD according to it
3. After running "Allrun" from the root folder successfully, I can't see my profiles in paraview.

I'm suspecting the blockMeshDict to be incorrect. Especially the vertices part.

In my STL file, vertex coordinates go approximately from -1.0e-002 to 6.0e+002.
I can't see how I should update the blockMeshDict to match those values.

Or maybe I'm completely missing the point ?

What am I doing wrong ?

NB: I've attached my STL file to this thread

lovecraft22 · April 9, 2012, 13:11

Hi Ma!
the problem is that you have 2D profiles. You need some 3D bodies to get them picked up by snappy otherwise you'll end up with your blockMesh mesh only…

Whether you want to run a 2D or 3D simulation, you still need a 3D geometry.

ma- · April 9, 2012, 13:35

Hello lovecraft22,

Thank you for your answer.
I indeed want a 2D simulation.

Actually, my profiles are extruded, but very thin (< 1mm). Isn't that enough ?

In a past experience, I meshed a single profile with gmsh, and I had to extrude a tiny bit out of it (1 mesh depth) and it went well.

My goal here is to reproduce it with snappyHexMesh and 3 naca profiles.

lovecraft22 · April 9, 2012, 14:06

In my experience sHM messes a little bit with thin geometries, that means that if you have a thin surface you need a very fine mesh to avoid sHM to bridge across the surface. So, I would suggest you to extrude your profiles a little bit and have a blockMesh shorter than their span. So, if you extrude them by 50mm you block mesh should be 40mm wide. This way you can then generate the mesh to perform a 2d simulation.

One your mesh is done you'll end up with a 3D mesh. You'll then need to extrude one of the faces to have a 2D mesh.

Always remember that openFoam can perform 2D simulation but the geometry and the domain need to be 3D anyway.

I hope that's clear, if is not, just let me know.

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April 9, 2012, 13:11		#2
lovecraft22 Senior Member lore Join Date: Mar 2010 Location: Italy Posts: 460 Rep Power: 18	Hi Ma! the problem is that you have 2D profiles. You need some 3D bodies to get them picked up by snappy otherwise you'll end up with your blockMesh mesh only… Whether you want to run a 2D or 3D simulation, you still need a 3D geometry.

April 9, 2012, 13:35		#3
ma- New Member Join Date: Apr 2012 Posts: 2 Rep Power: 0	Hello lovecraft22, Thank you for your answer. I indeed want a 2D simulation. Actually, my profiles are extruded, but very thin (< 1mm). Isn't that enough ? In a past experience, I meshed a single profile with gmsh, and I had to extrude a tiny bit out of it (1 mesh depth) and it went well. My goal here is to reproduce it with snappyHexMesh and 3 naca profiles.

April 9, 2012, 14:06		#4
lovecraft22 Senior Member lore Join Date: Mar 2010 Location: Italy Posts: 460 Rep Power: 18	In my experience sHM messes a little bit with thin geometries, that means that if you have a thin surface you need a very fine mesh to avoid sHM to bridge across the surface. So, I would suggest you to extrude your profiles a little bit and have a blockMesh shorter than their span. So, if you extrude them by 50mm you block mesh should be 40mm wide. This way you can then generate the mesh to perform a 2d simulation. One your mesh is done you'll end up with a 3D mesh. You'll then need to extrude one of the faces to have a 2D mesh. Always remember that openFoam can perform 2D simulation but the geometry and the domain need to be 3D anyway. I hope that's clear, if is not, just let me know.