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-   -   rotational periodicity with enGrid (http://www.cfd-online.com/Forums/engrid/129005-rotational-periodicity-engrid.html)

overdrive January 26, 2014 09:51

rotational periodicity with enGrid
 
Hey everybody,
I want to mesh only one blade of a three-blade-propeller (120°cylinder) with enGrid. Can someone tell me how to do the setup of rotational peridiocity? In general, is that possible?
Kind regards

wyldckat February 1, 2014 09:29

Greetings overdrive and welcome to the forum!

Are you referring to the set-up of the boundary conditions or to how the mesh can be generated for 1/3 of the geometry and then copied to the other 2 parts?

Best regards,
Bruno

overdrive February 3, 2014 10:47

Hello Bruno, first of all: thanks for your reply! No, actually, I just want to set up periodicity and to define periodic faces (like the way you can do it in icem) in order to calculate just one third of the whole geometry but taking into account the flow of the two other parts! Do you know what I mean?

wyldckat February 4, 2014 15:55

Hi overdrive,

Mmm... well, it really depends on where you'll be using the mesh.
I say this because enGrid only does case set-up for OpenFOAM and it's still a bit limited on that topic. The best it can do is "symmetry" or "patch", which neither are what you're looking for.
Nonetheless, a bit more information on this topic for defining boundary conditions in enGrid is shown here: https://github.com/enGits/engrid/wik...ary_Conditions

For example, if you want to export the case for OpenFOAM, then first export in enGrid the case as-is (or just the mesh); then you'll need to use OpenFOAM's createPatch or manually edit the file "constant/polyMesh/boundary" to define the that each side of the 120 degree domain is a rotational cyclic patch.

I assume that if you export the mesh for any other CFD solver, you'll need to do something similar, namely to reassign the patches to cyclic/periodic patches.


Although... perhaps you're asking about how to ensure that the surface mesh on each periodic patch is topologically identical? Namely has the same number of faces, points and they only differ on the plane they are working? If this is the case, then I don't know how this is done directly in enGrid, if at all possible.
The best I'm aware of requires using Blender as an intermediate surface mesh manipulator, where:
  1. First mesh one of the periodic patches in enGrid.
  2. Then export the mesh to Blender.
  3. Delete the other patch in Blender and copy the meshed patch onto the missing patch.
  4. Use Blender to do some surface mesh stitching.
  5. Export from Blender to enGrid.
  6. Do the remaining surface mesh in enGrid, without modifying the periodic patches.
Beyond this, I suggest that you use enGits on-demand support, to get a quicker answer: http://engits.eu/en/support ;)


Disclaimer: I do not work at enGits, I just mostly help with the ports for Windows.

Best regards,
Bruno

overdrive February 5, 2014 10:15

Hiya Bruno, nice to read your advices, thanks! Actually you're right, I want to export the case to OpenFOAM. I am not sure but I think it's necessary to ensure that these periodic patches are topologically identical, even with OpenFOAM and createPatch / cyclic type.
I think, I will make use of the enGrid support to ask for how to create such topologically identical patches before checking out Blender;-) but huge thanks for your ideas!
kind regards,
overdrive


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