【作者】 陈波；

【导师】 李万平；

【作者基本信息】 华中科技大学 ， 流体力学， 2006， 硕士

【摘要】 近壁圆柱绕流不管是在实际应用还是在理论研究中,都有其重要意义。由于壁面的影响,使得尾流区内旋涡的产生和脱落发生很大的变化,同样圆柱的存在也对平板壁面边界层内流场产生巨大的影响。正因为近壁圆柱绕流问题的复杂性和实际意义,人们至今还保持着浓厚的兴趣关注着这一问题的深入研究。近壁圆柱附近的壁面泥沙沉积现象由于在现代工程问题中的重要性,引起了人们的重视。在用粒子图像测速仪(PIV)进行近壁圆柱绕流实验时,在圆柱下游往往会观察到壁面出现积沙现象。壁面积沙现象涉及到近壁圆柱绕流流场速度分布及涡结构的特征。为了能够深入了解积沙线的形成过程及其与尾流-边界层相互作用的关系,本文应用粒子图像测速系统对近壁圆柱绕流流场进行了详细的实验研究,为近壁圆柱尾流的壁面积沙现象提供机理解释。实验在水槽中进行,采用跟随性极好的均匀小粒子作为示踪粒子。在湍流边界层充分发展的区域植入圆柱,在两个Reθ(动量损失厚度雷诺数)下,改变间隙比G/D(圆柱与壁面之间的间隙G对于圆柱直径D的比值),对各种情况下的尾流场进行测量,得到从0～1.5的12个间隙比下的两个不同直径圆柱体绕流情况的尾流场和积沙线数据。文中对系综平均场和瞬时场的速度分布及涡结构进行分析,同时观察积沙线的形成过程。结果表明由于圆柱尾流和平板壁面边界层相互作用,在圆柱下游平板壁面处发生边界层分离。在周期性尾流中有相对稳定的分离区和壁面附着涡,流体运动挟带到此处的粒子速度减小发生沉积而形成积沙线。积沙线的出现表现了近壁尾流的涡结构特征。观察表明,出现积沙线要有两个条件,一是有来流输送充足的粒子提供沙源,二是流体局部滞止使得粒子稳定聚集。当G/D=0时,壁面只有一条积沙线;从较小G/D直到G/D=0.1,壁面会出现两条积沙线;当G/D>0.2,又只出现一条积沙线;当圆柱对壁面影响减弱后,生成积沙线的条件不再存在,光滑壁面上粒子不能明显沉积。更多还原

【Abstract】 Flow around a circular cylinder near to a plane wall has been a subject of research due to its practical and physical importance. Because of the effect of the wall, the wall boundary layer is dominant, which makes the vortex shedding in wake different from those on flow around an isolated circular cylinder. Simultaneity flow in wall boundary layer is seriously affected because of the cylindrical existence. Because of this complexity and practical use, there still many scholar pay a lot of interest in studying this problem.When carrying on experiments of the flow past a circular cylinder near to a plane wall using Particle Image Velocimetry(PIV),the sand accumulation line is found on the plane wall downstream of the cylinder. This phenomenon refers to the characteristics of velocity distribution and vortex structures in the wake of flow around a circular cylinder near to a plane wall. In order to have a further understanding of the process that forming the sand accumulation line and the relationship between sand accumulating and the interaction of the boundary layer and the wake, we have conducted a very particular experiments.The circular cylinders, having two different diameters, are set in a fully developed turbulent boundary layer, and the particles seeded in the water can follow the flow very well. Under two Reynolds numbers of momentum loss thickness with 12 gap ratios from 0 to 1.5, the velocity vector distribution and the data of the sand accumulation lines are obtained.Analyzing the velocity distribution and the vortex structure of the ensemble average flow field and the transient flow field and observing the process forming sand accumulation line indicate that the separation take places due to the interaction of the wake cylinder and the boundary layer of the plane wall. There are relatively stable separate zone and wall attached vortex in the periodic wake flows. The speed of particles entrained by flow reduced and deposes there. Some characteristics of the vortex structure that in the wake of cylinder near to a plane wall can be learned by the appearance of the sand accumulation lines.更多还原