Many important flow analyses such as helicopter rotors, turbomachinery and coaxial propellers involve surfaces in relative rotational motion. While some instances can be addressed using a single rotating domain, the current focus is on situations where such a representation is inadequate and a sliding interface must be introduced to properly separate domains in relative motion. The approach is configured for a Cartesian grid framework where procedures to generate a grid about a triangulated surface and perform various clipping operations upon triangular elements are already available. This paper details the technical approach, in particular methods for evaluation of overlap areas at the sliding interface, enforcement of flux conservation, and development of flux correction terms, and also provides methods applicable at interfaces that terminate on a solid surface. Also described here are supporting operations tasked with arranging and enumerating the sliding interface elements, generating the mesh about the bounding surfaces (including sliding interface triangulations), applying the geometric transforms to impart rotational motion, and augmenting the governing equations to account for mesh motion and resolution of the velocities into convenient reference frames. The paper also provides motivation for this work, w ith emphasis on work on counter rotating open rotors (CRORs). The details of the sliding interface approach for this application are described and demonstration calculations on a representative CROR system are presented, including comparison with experiment. Finally, methods for extension to unstructured grids other relative motion scenarios will be outlined.
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