【作者】 张燕；

【导师】 王道增；

【作者基本信息】 上海大学 ， 流体力学， 2005， 博士

【摘要】 本文的研究对象为受横流影响的冲击射流。横流冲击射流近区存在射流剪切层、冲击效应、壁射流及其与横流的相互作用,流场中涡旋结构的形成、演化特征和涡间相互作用机制复杂,目前在国内外尚缺乏深入研究。对横流冲击射流中涡旋结构随时间、空间的发展过程及其与环境横流、底壁边界相互作用的研究不仅能促进其在环境工程、水电工程等实际工程问题中的应用,而且能揭示流场中各种涡结构的内在机制和演化特征,为实施流动控制和改善流场特性提供基础。 本文采用水槽实验与数值研究相结合对横流冲击射流近区流场特征和涡旋结构进行了详细研究。实验研究采用激光诱导荧光(LIF)流动显示技术和PIV流场测量,主要研究环境水深、流速比等流动参数对横流冲击射流近区非定常流动特性和涡旋结构特征的影响;数值研究采用三维非定常大涡模拟(LES),主要分析射流主体流动形态随时间、空间的发展演化以及射流在横流和底壁共同作用下形成的三维涡旋特征等,与实验结果互为验证和补充。 根据实验LIF流动显示和PIV流场测量结果,冲击射流与横流相互作用形成的剪切层涡、射流尾迹涡、上游壁面涡和scarf涡随流动参数的变化,表现出不同的非定常流动特性,而且各种涡之间存在相互作用。射流主体迎流面和背流面初始形成的剪切层涡存在三种分布形式,即近似对称型、交替型和螺旋型。随射流的发展,受横流影响以及涡间相互作用,剪切涡均会发展为围绕射流主体的螺旋型模式。迎流面剪切涡的分布较为规则,在发展过程中卷吸环境流体,涡间存在较明显的间隙。背流面射流尾迹涡不仅有水平面内的旋转和拉伸变形,还存在垂直平面内的扭转,表现出明显的三维流动形态。相邻涡存在旋转方向相同以及旋转方向相反的多种排列形式,在射流主体后缘还有多条尾迹涡横向并列分布情形,其流动形态及形成机理均不同于以往研究较多的壁面边界层与射流作用下形成的横流尾迹涡结构。 射流到达底壁形成冲击后在射流主体上游出现大尺度壁面涡结构,其扩展范围和非定常运动特性依赖于冲击效应和横流影响。随流速比的减小或环境水更多还原

【Abstract】 Investigations on an impinging jet under the influence of crossflow are carried out in this dissertation. There exit jet shear layer, impingement on the bottom wall, interactions between the induced wall jet and the ambient crossflow in near field. There are few intensive studies of the impinging jet in crossflow at home and abroad due to the flow complexities such as the formation and evolution of the vortical structures, interactions between vortices, while researches on the temporal and spatial evolving of these vortical structures can promote the practical applications in environment engineering, hydroelectricity engineering etc. as well as reveal the inherent mechanism and development of the vortical structures and provide the basis for flow control and improvement.Both experimental investigation and numerical simulation are conducted to obtain the detailed flow features and vortical structures in the near field of the impinging jet in crossflow. For the experiment, LIF (laser induced fluorescence) flow visualization and PIV (particle image velocimetry) measurement are adopted to study the effects of the flow parameters on the unsteady characteristics of the flow and vortical structures. For the numerical simulation, unsteady three-dimensional LES (large eddy simulation) is used to obtain the temporal and spatial evolving of the jet and the 3D configuration of the vortices formed by the interactions among jet, bottom wall and ambient crossflow. Results from experiment and computation can be validation and complement to each other.It can be inferred from flow visualization and PIV measurement that the shear layer vortices, jet wake vortices, upstream wall vortex and scarf vortex vary with the flow parameters and there exist interactions in various vortical structures. There are three arrangement types of the original vortices in the upwind and lee sides of the jet, namely approximate axisymmetry, alternation and helicity while any arrangement type will grow into helical one during developing with the main jet and being affected by the crossflow and interaction between vortices. Vortices in the upwind shear layer will form a more regular arrangement than those in the lee side, and there exist obvious intervals between vortices. The jet wake vortices occurring in the lee side of the jet show an evident three dimensional movement including the spin and stretch in the horizontal plane as well as the torsion in the vertical plane. And the global feature of the jet wake vortices appear to be very complicated, there exit not only the alternating circulation but also the same rotation direction for vortices更多还原