邊壁效應對漸近球後方渦環發展的影響

Wall Effects on the Evolution of a Vortex Ring Behind an Approaching Sphere

林雍釗(Yong-Jhao Lin)

指導教授 ： 蔡進發

共同指導教授 ： 沈弘俊(Horn-Jiunn Sheen)

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.01988

摘要

本論文以實驗探討不同雷諾數及史托克數下，邊壁效應對球本身運動及流場渦度的影響，當球體在液體中運動，會受液體黏滯力及虛擬質量力影響，使球體運動有減速的情況，進而影響後方渦環結構，當球體靠近邊壁，流體力受邊壁影響，導致球體周圍的渦環強度也有明顯的變化。
本實驗以鋼球、玻璃球及壓克力球進行球沉浸在水面下的單擺運動實驗，並以不同比例的甘油與水混合液來控制液體黏滯性，藉以達成不同雷諾數下的運動。利用雷射分光光頁照亮單擺運動平面，測量球前後流場的變化，在相同雷諾數下，進行有無邊壁的實驗。此文中，雷諾數以分析位置中最大速度來表示，實驗結果顯示，當有邊壁存在且Re≧80，漸近球在距離邊壁0.1~0.9球直徑時，速度有明顯的下降，在Re≦50，漸近球在距離邊壁一個球直徑或更遠減速。
本實驗以球距邊壁前2D~0D計算渦度場，結果得出在球運動過程中(Re=75~88)，隨著球接近邊壁，漸近球後方渦環的寬度變大，而渦環高度除壓克力球外，有上升現象。漸近球撞擊邊壁，使球周圍渦度強度減小，且球前方流場邊界層形成，在邊壁上下兩邊有集中之渦度產生；在邊壁影響距離的位置，球後方渦環高度上升。

關鍵字

邊壁效應 ； 渦環發展 ； 單擺運動 ； 雷射分光 ； PIV

並列摘要

This thesis discusses the wall effects on the evolution of a vortex ring behind an approaching sphere on different Reynolds number and Stokes number, sphere motion in fluid got a deceleration were influenced by fluids drag forces and added mass forces, and then affected the vortex ring structure, when spheres approach the wall, hydrodynamic forces were influenced by wall effects, flow around spheres of vorticity had obvious changes.
This experiment used steel、glass and PMMA spheres to proceed pendulum motion in liquid, and used different ratio of glycerien and water to control viscosity, in order to simulate different Reynolds numbers character of flow motion, to used two light sheet light pendulum motion plane, and measure around sphere flow filed change, with or without wall to operated and to proceed same Reynolds number experiment, in this thesis, the max Reynolds number were presented max velocity on analysis position. The results obviously when with wall and Reynolds numbers at Re≧80, an approach sphere at 0.1~0.9 diameter, velocity has obviously decreased, Reynolds numbers at ≦50, an approach sphere at 1.0 diameter or early had obviously decreased.
This thesis calculated vorticity of sphere position at 2D~0D, the result where spheres motion in Re=75~88 were sphere approaching the wall, behind sphere of the vortex ring width was increased and the vortex ring height was increased except PMMA, and the vorticity were decreased on flow filed of around sphere. The sphere ahead boundary layer were produced by approach sphere and motion on the wall, top and down of the wall produced vorticity. The vortex ring behind sphere had increased on the wall influenced distance.

並列關鍵字

wall effects ； vortex ring evolution ； pendulum motion ； laser splitter ； PIV

參考文獻

謝秉昇 “背景渦度下雙渦漩交互作用之水工實驗” 台大應用力學所 2004。

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