| Summary: | 碩士 === 中興大學 === 土木工程學系所 === 94 === The characteristics of horseshoe vortex system near the juncture of a square cylinder and a base plate were studied experimentally. The incoming flow speed accelerates impulsively from zero to a constant value. The structures of horseshoe vortex were observed at low Reynolds numbers equal to 200, 400, and 1000 using particle image velocimetry (PIV) and flow visualization techniques. The characteristics of starting horseshoe vortex system were analyzed, including the position of primary vortex core, the position of stagnation point on the model, down-flow velocity profile and the circulation of primary vortex, respect to dimensionless time parameter T.
In this study, it is found that the shapes of down-flow velocity profiles are similar due to the same vortex structures. The relationship between flow characteristics and dimensionless time parameter T can be described by log equation using regression analysis. The similarity of the position of stagnation point on the model is presented. It is noted that the similarity of the position of stagnation point on the model can be obtained for all conditions, using dimensionless length parameter ys/H and dimensionless time parameter T/Ts.
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