CGNS problematic import in Pointwise
 

Hello,

I would like to ask about 2 issues regarding Pointwise .cgns import.

1. I have a 2D map-structured mesh around an Eppler airfoil that I want to simulate using SU2 code. I need to create the .su2 format, therefore I will use Pointwise to transform a .cgns file into .su2. The .cgns file is exported from FLUENT (see pic 1).
When I import the .cgns file into Pointwise, the mesh is automatically diagonlised (triangular cells),(see pic 1). The diagonilize option is not enabled. Why is this happening? I verified that the mesh is been altered (and it is not just an optical problem) by exporting a .cgns by Pointwise and importing it on Tecplot (see pic 3).

2. When I try importing a 3D .cgns mesh (again exported by FLUENT), I receive an error "Detected 1 unsupported entity. Unable to continue".

Do you know how can I solve these issues?

Thanks,
Spyros

Hello Spyros:

Pointwise only currently understands hex cells in the context of a structured grid. If the CGNS file from Fluent has unstructured hexes, Pointwise can't parse it and gives that error message.

In 2D, Pointwise sees the quads and triangulates them before import because it does understand unstructured triangles (not unstructured quads).

See if you can export the grid in a structured grid format like PLOT3D.

Hello jchawner,

Thank you for the reply. Unfortunately, nothing of these worked. I do not have a way for exporting in a structured grid format like PLOT3D and my attempts in using various forms failed: "Invalid file - no data imported".

Regarding the 3D CGNS file, this is a structured hex cell mesh. Therefore, based on what you suggested it should have been imported, if i understand your reply correctly. Furthermore, in the future i will need importing cgns files of hybrid meshes. Does this mean that i will not be able to import such cgns meshes in Pointwise? Is there another format that can be easily read in Pointwise?

Thank you very much,
Spyros

If you exported the CGNS file with Fluent, the mesh will be unstructured. While you may have originally created a structured mesh and it still looks like a structured mesh, when it's imported into Fluent it loses the topology information that make it truly a structured mesh.

The best way I see this working is to either a) build SU2 with CGNS import support b) use the CGNS-to-PLOT3D converter from the CGNS web site (http://cgns.sourceforge.net/Utilities.html) and then import the PLOT3D into Pointwise.

-Chris

Unfortunately, I don't see another solution. I cannot export in a structured format with PLOT3D and I will also need hyburd meshes anyway.

I wanted to avoid that though since it is recomended by the developers of SU2 in Stanford to prefer the native .su2 format.

I don't know how or where you're generating your meshes initially but you do know that Pointwise can export SU2 meshes directly. So if you create your mesh in Pointwise, none of this will be an issue for you.

Yes you are right in that.. But I will do my master thesis using SU2 among others and unfortunately I do not have time to learn new software.. This is the last choice for me if the cgns import in SU2 does not work.

Thank you very much for your reply,
Spyros

Cut out Pointwise
 

Hello Spyros,

Are you familiar with any programming languages, i.e. Python, Fortran?

Two years ago I was using SU2 and I made a SU2 mesh writer, I didn't find the format particularly difficult to write (I used fortran). I have also used the CGNS libraries and they aren't too difficult to use.

I would recommend Python and you can use PyCGNS module to read the mesh then just write it out using the inbuilt python write functions.

http://pycgns.sourceforge.net/

Sadly I don't have the file I created any more but if I can help some other way let me know.

As a final comment, when I was using SU2 I think I read in the guide that if you do compile with CGNS support then there is a way to get the mesh to be written to .su2 format at preprocessing.

Hope this helps,
Ben

Hi Ben,

Thanks for your suggestions.. I solved the problem by reinstalling the new edition of SU2 with CGNS support. In my initial installaiton, there was a problem with the cgns libraries and the -DNO CGNS directive. Now it can import CGNS files correctly so i just have to export my meshes into CGNS format. After the import, the serial SU2 code can transform the mesh into the native (.su2) format that can be used in later parallel computations.

But Thank very much for your suggestions anyway,
Spyros