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[Other] How does OpenFOAM know if dealing with sturctured or unstructured mesh

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Old   July 11, 2019, 17:14
Default How does OpenFOAM know if dealing with sturctured or unstructured mesh
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Hi everyone,

I know this is a well discussed topic in this forum but I have not found an answer on my question so I hope you can help:

I was wondering how OpenFOAM "decides" whether it is dealing with a sturctured or unstructured mesh. I read in a textbook structured is much easier to handle as the belonging neighbours, faces, etc don't have to be stored as they are kind of defined by the structure of the mesh. Furthermore I understood at least when having structured mesh with same cell size (and optimally of hexahedral) the volume and area calculation for integral is much easier as well as interpolation due to orthogonality. (I know I am probably mixing definitions of structured and regular mesh here, but the question stays the same: how does OpenFOAM "know")

Nevertheless even for the simpliest blockMesh neighbour, faces, ... files are stored. So my question is if they are used for calculation anyhow and even a structured mesh is considered unstructured by OpenFOAM or if somehow in the files is defined how to handle the data which can be read by the code.

Furthermore I read about hybrid meshes. This would mean the files need to provide information how to handle the mesh for given areas of the mesh.

What about the refineHexMesh tool (for local refinement)? I assume it is generating structured meshes (starting from structured of course). Does this mean the whole "numbering" is rearranged? And what about the "transition" area. I guess the system of neighbouring cells is different from the rest of the mesh. How is this dealt with?

Thanks a lot in advance for any answer.
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Old   July 12, 2019, 02:44
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There are no structured meshes in OpenFOAM. Everything is unstructured, which is the most general way of doing things.
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Old   July 12, 2019, 15:18
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Thanks a lot for the fast reply.

Is there still any advantage of using blockMesh build meshes instead of for example snappyHexMesh build ones? I guess the orthogonality criterium is easier to handle but is there anything else?

I am especially thinking of using actuator line oder disk models instead of full meshes for representation of a turbine. Of course the mesh for full mesh needs to be much finer around the blades for a full mesh solution, but I always thought the structured uniform blockMesh grid has further advantages which I can't really give reasons for if OpenFOAM is handling the meshes as unstructured anyway.
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hybrid mesh, refinehexmesh, structured mesh

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