Mixing Interface boundary conditions are very strong tool in CFD. It is being used mainly for steady state simulations. The big benefit of mixingInterface is the averaging of quantities (vanishing the rotor position). Meshes of different elements and even of different size, position, topology and orientation can be inter-connected.

Special averaging is employed. At the interfaces, every scalar quantity is mapped with help of its radial (circumferential) average. The velocity vector at the interfaces is reconstructed from mass flow (also from pressure if compressible) and averaged velocity angles.