Water Pump - Single-Region Approach
Single region approach is of course also possible. Moreover, single region approach is intuitive simplification of the multi-region one. For case with full wheel approach at the interfaces there can be used OpenFOAM AMI (arbitrary mesh interface) boundary condition.
This tutorial deals only with multi-region approach. The reasons are following: multi-regioning allows unsteady simulations, better converges, supports wider range of methods (averaging, BCs).