Reply To: General questions regaring the new grid refinement functionality
1) You can ignore the geometry error here. This is a remnant of the current geometry validity conventions (e.g. that a material 0 (inactive) cell must not directly border a fluid (material 1) cell) only holding for uniform grids. You can remove the check method until we have a resolution-transparent geometry model in a future release, if this message bothers you.
The current release of the refinement module is a prototype that requires deep OpenLB knowledge to transfer to other cases. We are working on a user-friendly way to generate the refined meshes but this will take time.
2) Validation is in progress. In any case, grid refinement should always be evaluated for the specific application and LB models as it is a very active and unsettled topic. E.g. any refinement introduces an additional error source that can only be ignored after careful consideration and numerical tests.
3) This is a good example for the difficulty of refinement in LBM: It depends. A simple approach is to only couple bulk cells (as refinement schemes are commonly evaluated only in the bulk). For 3D Schäfer-Turek (cylinder3d), not coupling the wall cells suffices in my experience.
4) It should if the non-equilibrium is in fact obtained as the difference between current populations and their second-order equilibrium. If this doesn’t hold the coupling needs to be adapted.
Please also note that the public version implements a simplified version of the vertex-centered scheme by Lagrava (it uses very simplified spatial interpolations). A full version as well as support for cell-centered couplings are in the works.
The work on grid refinement is currently limited mostly by the number of developers working on this, if you are interested I’d be happy for any help.