Be wary of flow moving backwards across stage or frozen rotor interfaces. Because of the approximations implied by these interfaces, flow moving upstream and downstream on the same interface will lead to unphysical results. Try relocating the interface to prevent this from occurring.
As an example, Figure 11.7: Domain Interface Between Blade Rows in an Axial Machine shows two blade rows of an axial machine with a frozen rotor interface between them. The flow moves from left to right everywhere except in a small region just downstream of the trailing edge of the first row of blades. In this case, the domain interface, shown as a dashed line, should be located to the right of this region, as shown.
