| Summary: | 碩士 === 國立臺灣海洋大學 === 機械與機電工程學系 === 94 === Abstract
In this research, two 3 cm x 3 cm square cylinders were aligned in a vertical water tank. The flow field characteristic modes, drag coefficients and vortex shedding properties were explored with changing the Reynolds numbers, spacing ratio and downstream cylinder’s angles of attack. Utilizing the particle tracking flow visualization (PTFV) technique was applied to observe the flow fields. The flow field can be classified into three characteristic modes, that is, the single mode, reattach mode and jump mode under the conditions of variable Reynolds number, changeable angles of cylinders and adjustable spacing ratio. Three characteristic modes are classified, that is, mode I, mode II and mode III, under the conditions of fixed Reynolds number, fixed upstream cylinder and angle-adjustable downstream cylinder. The particle image velocimetry (PIV) was applied to analyze the velocity, streamline, vorticity and vortex sequence in different modes. Furthermore, the trend of these modes can be found by the drag and vortex shedding frequency. The results show that, in the viscosity-dominated flow fields, the non-dimensional vortex shedding frequencies decrease when the Reynolds numbers are raised. Additionally, in the inertia-dominated flow fields, the frequencies change coordinately with the Reynolds numbers. The topological analysis was also utilized in this research to verify the experimental results.
Keyword: Twin square cylinders, PTFV, PIV, Vortex shedding
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