[chegdan]

Somehow I didn't see that you had provided a case in your previous post, so i took a look just now. The curved surface on the channel you are meshing has some bad quality surface mesh triangles (see attached). Also, because the triangles are so bad there is practically no gap to mesh so I would expect behavior like you are seeing with bridges between your inlet and outlet regions. For small features like your gap, it works well to really have a high quality STL surface in areas of importance. Also, snappyHexMesh does not work on analytical surfaces (i.e. CAD) and we can only get the maximum resolution in our mesh that is present in our surface file, so a bad STL will give us a poor mesh.

[enginpower]

@chegdan, so you're suggesting me to improve the STL file. Right?

To do that, I have to create a better surface mesh on Salome. Right?
How do you suggest me to set parameters on Salome, to create a good exported STL? Or what do you suggest me to improve anything to get a good STL?

Actually, watching it on Salome, it doesn't seem to be so currupted. I check everything, according to the tutorial to have a connected surface mesh. I don't know why it seems a so low quality mesh

Thanks, so much

[chegdan]

I'm not a Salome expert so I can't advise on the best settings. I personally, use onshape since that produces some nice STL surfaces from CAD (and they work well with snappyHexMesh). There you can set the STL export to a "fine" level or do a custom triangulation and use your best judgement. Just try to make sure all your edges are present and the triangles on the curved portion (where the gap is) are smaller than the gap.

[enginpower]

Waiting for some Salome expert, because it is open and this is more fitting my project purpose, I want to try onshape, because I read it is also based on a open source code. But apart from importing the CAD file and setting the export options (I'm imagine how to use it), how can I set the different patches for the boundary conditions? In Salome, following the tutorial indicated above there is an explained procedure to do that, what about onshape.com ? Anyway I'd like to try too, and helps are welcome!

By the way, is there some Salome expert that can see my case? What's wrong with export or elaboration with Salome?


Thanks to @chegdan and to who wants to help me

[enginpower]

Originally Posted by chegdan

I'm not a Salome expert so I can't advise on the best settings. I personally, use onshape since that produces some nice STL surfaces from CAD (and they work well with snappyHexMesh). There you can set the STL export to a "fine" level or do a custom triangulation and use your best judgement. Just try to make sure all your edges are present and the triangles on the curved portion (where the gap is) are smaller than the gap.

Hi @chedang,
I tried Onshape, and also the custom export of STL.
What is it not clear is how do you individuate specified surfaces?
How do you define inlet, outlet, wall, etc...

I think you follow a procedure that is missing to me. Could you explain better this:
-export from onshape (just use a custom or fine setting?)-->setting SnappyHexMesh(how do you individuate surfaces?)-->mesh getting surfaces for boundary conditions (how do you get surface where to set boundary conditions?)

Thanks for any helps

[kandelabr]

Could you cut the thin wall out of the model, create the cut part with blockMesh and everything else with snappy and then join meshes with AMI? blockMesh has no problems with a few million cells

[enginpower]

What is AMI?

Thanks

[kandelabr]

Arbitrary Mesh Interface
https://openfoam.org/release/2-3-0/non-conforming-ami/

I would do the following:

1. cut the thin wall from your model
2. divide the surface so that a patch would remain where the pipe was cut away
3. use snappyHexMesh to mesh the model and specify an insane refinement level only on the patch mentioned above (where the thin wall connects)
4. create a new mesh using blockMesh that would match the shape of the thin wall
5. merge meshes
6. set AMI boundary conditions where meshes connect.

roughly that should do. cell size on connecting patches should be approximately the same, i guess.
i followed this tutorial for setting up AMI and boundary conditions (but my problems are elsewhere ): http://www.cfdsupport.com/Turbomachi...l/node159.html

[enginpower]

Sorry,
but I can't see in your link

i followed this tutorial for setting up AMI and boundary conditions (but my problems are elsewhere ): http://www.cfdsupport.com/Turbomachi...l/node159.html

a reference how to set an AMI.

Could you check again, or indicate me where exactly it is explained in linked web page?

Thanks!

[kandelabr]

in the 'script' section there is the whole script:
https://www.cfdsupport.com/Turbomach...l/node179.html

check steps after reconstructParMesh; createPatch and changeDictionary. You'll need createPatchDict and changeDictionaryDict for those steps to work and you'll find the contents of them in previous tutorial steps. They just create patches you need for AMI.

Also check out tutorials from Tobias Holzmann, very good stuff. start with the 'run' script and see what it runs.

http://www.holzmann-cfd.de/index.php...ving-rotor-ami

good luck