Transformation of flow structure on a rotating wing due to variation of radius of gyration

摘要

The flow structure on a rotating wing (rectangular plate) is characterized over a range of travel distance at different radii of gyration. Travel distance is defined as the length of the arc subtended by the radius of gyration. Stereoscopic particle image velocimetry is employed to determine the volumetric flow structure, in the form of three-dimensional surfaces of the q-criterion, helical density, and downwash velocity. These representations are complemented by sectional patterns of vorticity and tangential velocity. An increase in the radius of gyration reduces the influence of rotation on the flow structure. At small radius of gyration, a coherent leading-edge vortex develops rapidly and then persists over a range of travel distance. At moderate radius of gyration, this leading-edge vortex is replaced by an arch vortex, which develops relatively slowly over a larger travel distance, and is eventually swept into the wake of the wing. The foregoing classes of vortical structures are associated with distinctive patterns of: helical density, which represents the axial vorticity flux through the three-dimensional vortex system; downwash related to the strengths of the components of the vortex system; and tangential velocity associated with the extent of reverse flow, or stall.