A numerical method is presented for the simulation of unsteady flows through turbomachine stages with unequal numbers of rotor and stator blades. The method solves the two-dimensional incompressible, unsteady, ensemble averaged, Navier-Stokes equations together with transport equations for the k -e turbulence model employed to simulate the effects of turbulence. The method employs an implicit pressure-based finite volume discretisation procedure. In order to simulate the flow in the rotor and

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... ator passages simultaneously, a sliding mesh methodology is developed which allows the mesh mapping the rotor domain to move in a sliding action relative to the static mesh which maps the stator passage. Phase-lagged periodic boundary conditions are implemented in the context of the implicit numerical method developed to handle unequal rotor and stator pitches efficiently. The effectiveness and accuracy of the method are assessed against data for a rotor/stator configuration with unequal pitches in adjacent rows of a low speed turbine.