Potential degradation/issue/bug in snappyHexMesh when creating cyclic patches
I came across this (potential) change in behavior in snappyHexMesh when trying to mesh a pipe with some components inside where inlet and outlet patches have to be periodic.
The original mesh was created some years ago with the 2.1.1 release (not available on our machine anymore so I can't recreate it or double check), by specifying the inlet and outlet patches of the pipe as cyclic in blockMeshDict. The mesh was then created successfully by snappy forcing the inlet and outlet patches to have the same mesh (see Fig. 1).
If the same procedure is used with the 2.3.0 or with the latest v1912, the mesh is created distorted (see Fig. 2).
If the inlet and outlet patches in blockMeshDict are set back to "type patch", the grid also goes back to nice and smooth (see Fig. 3) but at this point the two faces do not match and "type cyclic" can't be used (cyclicAMI works but not an option here for solver's reasons).
I've then tried to mesh a longer pipe with the inlet and outlet patches away from the components inside the pipe and set to "type patch" to end up with a regular surface mesh at both ends of the grid (see Figs. 4 and 5), but when I try to use the createPatch utility to switch from "type patch" to "cyclic", OF complains about matching the two patches even if the separation vector is provided and regardless of the matchTolerance.
(input dictionaries are all the same in the different tests performed).