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

• Main Authors: Yong-Jhao Lin, 林雍釗
• Other Authors: Jing-Fa Tsai
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/26970396457891982618

碩士 === 臺灣大學 === 工程科學及海洋工程學研究所 === 98 === 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.