[bhanu2204]

Hello every one,

I am trying to import a hybrid test mesh from gmsh to OpenFoam. The mesh basically three extended cubes as in the attached image 1. The left is completely unstructured, right is structured (transfinite) and the middle is unstructured but meshed with TransfQuadTri volume to facilitate the transition.

The issue is the face connecting the transfinite and TransfQuadTri volume is separating the mesh into regions. The red coloured face in image 2.

The checkMesh result is fine as attached in the checkmesh file here. Except for this.

Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
*Number of regions: 2
The mesh has multiple regions which are not connected by any face.
<<Writing region information to "0/cellToRegion"
<<Writing region 0 with 49935 cells to cellSet region0
<<Writing region 1 with 6859 cells to cellSet region1

Any ideas on how could I include this single separating face into the internal volume. I tried stitchMesh, removeFaces, zipUpMesh but no positive result. Any idea if this can be imported to another opensource meshing tool and merged into mesh ?

I will be happy to provide any further details you might need. Thanks for your time.

Cheers.

[jgross]

Hi OFers and Bhanu,

I am getting something quite similar when I use gmshToFoam for a 2D mesh with a structured boundary layer. The boundary layer has been included in the same physical groups as the rest of the domain, but when I use gmshToFoam, the boundary layer is designated it's own patch.

I guess this is because gmsh designates the structured region as its own mesh partition, and gmshToFoam uses the mesh partitions to create the patches.

This wouldn't be as big of an issue if the boundary layer didn't span across a number of domains (as in the image included). This makes it almost impossible to change the boundary file such that the boundary layers are in their respective regions.

Does anyone have any help or advice to fix this?

J

[jgross]

As a follow up to the previous post, it seems my original issue is only true for the OF extend 4.0 version I was using. I tried it in OF5 and there was no issue with separating the structured boundary layer from the rest of the unstructured domain.

J

[jgross]

As another follow on, by using createPatch feature in OF, it doesn't matter if the two regions are separated. I can just combine them after using createPatch.

J

[bhanu2204]

Hi James,

Thanks for your comments on the post.

Probably, we are doing the hybrid meshes in a slightly different from each other. My process involves meshing unstructured volumes and structured volumes separately. Then, connecting them using TransQuadTri algorithm based volumes. If I am right, you might be using boundary layer field in gmsh and later developing unstructured mesh on it.

So, for me as in the image in the first post, the face separating the transfquadtri volume and transfinite volume is being seen as separating the mesh regions , when I do gmshToFOAM. I sorted this issues partially by creating separate geo and .msh files. Later using mergeMeshes feature of OpenFOAM. Followed by stitchMesh that literally stitches the two meshes and most importantly converts the connecting face as internalFace. Currently, the issue is arising because of the necessity to apply stitchmesh for multiple patches. This multiple patches issue, from my knowledge, doesn't have a perfect solution yet in OpenFOAM. Correct me, if I am wrong. I am still playing around in this aspect as this connecting face must be an internal face in my case.

I tried with OpenFOAM 5 but it still sees as different regions in the same cavity cases attached above. I tried to use createPatch, it works but the problem is it remains as a patch that needs a boundary condition to be defined. However, I need it as an internal face. Do you have any suggestions in this regard ?

In reality, I am doing full scale 3D ahmed mesh with hybrid grid ideology. The front curved parts will have the unstructured mesh enclosed in a volume.And the rest of the mesh completely structured. I am using the cavity case attached above to resolve errors using gmshToFoam and implementing the methods in ahmed body parallely.

My experience working with boundary layer field is very limited and may be my partial solution might not even work for you, considering there might not be a connecting face in your situation. Sorry for that. From your knowledge, can you also comment if it is possible to generate a structured boundary layer (Edit: Using boundary layer field) around front curved parts of 3D ahmed body ? I tried but failed miserably in that.

Also, I am trying cyclicAMI with transform option as coincidentFullMatch. I will let you how it goes.

Let me know if you need any other details. Thanks for your comments again.


Cheers.

[jgross]

Hi Bhanu,

You're right. I am using boundary layer field in Gmsh, which is fine for 2D. I haven't tried it for 3D, but my guess is that isn't any where near as good.

In general, Gmsh seems to be really good for 2D stuff, but is still very much in development when it comes to 3D. I might suggest you to try cfMesh. It's similar to snappyHexMesh, but it's way much easier to use.

As for the other questions, sorry I am unable to be of assistance as I don't have any experience with it.

Best of luck,
James