Move special case treatments to appropriate classes: VelocityGradients
For (fcstaggered) freeflow a normal velocity gradient at the boundary can only be computed if the velocity is specified through Dirichlet boundary conditions. While the velocityGradients
uses outsideVolVars
(=inside at non-Dirichlet boundaries?), the slip velocity momentum flux allows to specify this gradient as an optional parameter. Instead, the velocityGradients
could specify treatment of edge cases in a central spot such that other classes can apply it in a consistent manner.
This should be accompanied with an easily accessible option to switch such classes if you adapted them, e.g. through access to publicly readable model traits.