[AlexMarvel]

I am reading the user guide of OpenFOAM, it mentions that "Every cell must be convex and its cell center inside the cell." but the block mesh supports non-straight edges, possible options are: arc, spline, polyline, Bspline, line.
If the edges are splines, there must be both convex and concave cells.

My question is:
1. The rule of "Every cell must be convex and its cell center inside the cell." is a mandatory requirement, or it is just a recommendation of OpenFOAM?
2. If both convex and concave cells are acceptable, is this statement in the OpenFoam User guide obsolete and it needs to be modified and fixed?

Here is the link to chapter 5.1.3 of the OpenFoam user guide:
https://cfd.direct/openfoam/user-gui...24-1750005.1.3

Here are some screenshots:

[wyldckat]

Quick answer, albeit over a year late, so for future reference:
The idea is that this edge design is just a generation function for calculating the positions of the vertices, each meshed edge of a cell will not take the shape of such a function.

For reference:

• v9 version of the User Guide at CFD-Direct: https://cfd.direct/openfoam/user-gui...-1880005.3.1.2
• v8 version of the User Guide at CFD-Direct: https://cfd.direct/openfoam/user-gui...-1880005.3.1.2

The concept of the convex cell is that the center of each face of a cell can be seen from the center of that cell, from the inside of the cell... without any other face getting in the way of the straight line that connects face center to cell center.