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WiWo March 18, 2010 12:10

Face orientation in blockMesh
Hi Foamers,

I've got a question concerning the pre-processing tool blockMesh.

In many references (including the OF user's handbook) I found clear instructions about how to define faces (e.g. defining patches). The key is to keep the orientation of the face in mind - thus the convention states, that "The order in which the vertices are given must be such that, looking from inside the block and starting with any vertex, the face must be traversed in a clockwise direction to define the other vertices." This convention sounds perfectly reasonable in order to have an unambiguous direction of the face normals.

Now, I happen to mess up the orientation (define it counter-clockwise) of one patch in the blockMeshDict in a mesh of mine. Neither blockMesh nor checkMesh did complain. When I recognized my error I corrected the patch (now everything is defined according to the conventions) and created the mesh anew.

The strange thing now being, that there is NO difference at ALL between the output of blockMesh (points, faces, neighbour, owner, boundary) between the case where I used the incorrect blockMeshDict and the case where I used the correct one. I compared the files line by line using 'diff'!

Now if there is a difference in the face orientation (and consequently the orientation of the face normal), then the files should show some different entries, or shouldn't they? Is blockMesh writing anything to any files except the ones I mentioned? How is OpenFOAM determining the face normals?

Is there somebody who can shed some light on that? As you might guess, I'm a little confuses about that.


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