| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 96 === Numerical simulations with unstructured spectral element method were applied to the study of the phenomenon of cross flow around two cylinders. According to the research of Strykowski(1985), vortex shedding could be drastically inhibited with a control cylinder which in size is much smaller compared to the main cylinder. The purpose of this research is further focus on different parameters of control cylinder for drag reducing, lift increasing, and vortex inhibition. The Reynolds number of all simulations is 100. Both passive and active controls were studied. For passive controls, effects of position and gap between two cylinders were systematically investigated and three modes of flow patterns were classified. It was also found that 15% of drag reducing could be achieved at fully inhibition mode and maximum 35% of drag reducing could be achieved at partial inhibition mode. Based on different types of flow patterns, vibration was applied to the control cylinder for active controls. Effects of vibration amplitude and frequency were studied. Due to the transition between subcritical and supercritical flow, the lock-in area at fully inhibition mode is much different than previous literatures.
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