| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 89 === The particle tracking flow visualization method (PTFV) and particle image velocimeter (PIV) are used to obtain a clear picture of the vortex evolution process on suction surface of an impulsively started NACA 0012 wing. The experiments are conducted in a towing water tank. The formation, evolution, and shedding processes of the vortex system on the suction surface are observed and analyzed by the streak pictures of the particle images. Five characteristic vortex evolution processes are identified on the domain of angle of the attack and chord Reynolds number. The path-line patterns, instantaneous streamlines, and vorticities of various vortex evolution processes are presented. Stable vortex shedding in the wake is eventually established after the initial period of complex vortex evolution process on suction surface of the wing. Various types of instabilities in the wake, e. g., instability wave, surface vortex shedding, and bluff-body vortex shedding, are found to correspond to different evolution processes of surface flow. Topological critical points, separatrices, and alleyways are identified and discussed to elucidate the unsteady structure of the instantaneous streamline patterns. The topological rule for numbers of the singular points is verified. With the knowledge of the fundamental mechanisms of the evolution processes of the surface flow and vortex shedding. A circular-rod flow control technique is developed in order to observe the influences on the dynamic vortical system developing on the wing surface. In some regions, the rod can effectively suppress the vortex shedding in the wake and reduce the thickness of the separated boundary layer. The total effect may lead to a decrease in the drag.
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