Vortex Systems in Shallow Water

项目编号：CTS-9803734项目负责人：Rockwell本次研究的目的是对浅水涡旋的发展、相互作用和衰减有一个基本的了解。射流、尾流和混合层中的大规模旋涡运动发生在浅层自由水面的配置是多种多样的，如带有洪泛平原的明渠、沿河流的堤岸、水面水道的突然扩张、水库或湖泊入口、渠道或河流的汇合处、沿海大陆架带、桥台和孤立的钝障碍物，如码头、岛屿或植被丛。这些涡旋的发展对热混合、标量混合、通道和港口（seiches）的共振振荡、通道和河流汇合处的整体性能特征以及复杂通道的平均泄洪能力具有重要影响。此外，在所有这些配置中，由于涡旋运动引起的非定常和时间平均床层载荷，下垫层可能会受到冲刷或侵蚀。相对于大跨度切变层中涡的发展和相互作用，我们对以自由面和床（固体）面为界的浅水涡结构了解甚少。利用最近开发的高图像密度粒子图像测速技术（HID-PIV），可以获得二维和三维涡旋结构的第一个全局瞬时表示。这种方法将产生瞬时涡度的时空模式和相关的拓扑特征，对理解涡发展、涡-涡相互作用和涡衰减至关重要。这种方法为确定经典湍流统计量和混合效率提供了物理基础。更好地理解涡结构与河床冲刷侵蚀之间的关系，有助于开发新型的控制技术。在涡发展的近场过程中，微小的扰动会极大地改变初始形成的涡和快速发展的三维涡结构。在远场，大规模的准二维涡旋结构有望发展，控制形式将是床层摩擦和床层法向速度的时空变化；局部产生的二次涡度浓度可能对入射涡结构产生建设性或破坏性的干扰。2 1

Abstract Proposal Number: CTS-9803734 Principal Investigator: Rockwell The objectives of this investigation are to gain a basic understanding of the vortex development, interaction and decay in shallow water. Large-scale vortical motions in jets, wakes, and mixing-layers occur in shallow free-surface configurations are diverse such as an open channel with flood plains, an embankment along a river, a sudden expansion of a surface waterway, a reservoir or lake inlet, the confluence of channels or rivers, a coastal shelf zone, a bridge abutment, and an isolated blunt obstacle such as a pier, island or cluster of vegetation. The development of these vortices has important consequences for thermal mixing, mixing of scalars, resonant oscillations of channels and harbors (seiches), overall performance characteristics of channel and river confluences, and the averaged discharge capacity of complex channels for flood routing. Furthermore, in all of these configurations, the underlying bed may be subject to scour or erosion due to the unsteady and time-averaged bed loading induced by vortex motions. In contrast to vortex development and interaction in shear layers of large spanwise extent, very little is known of the vortex structure in shallow water bounded by a free-surface and a bed (solid) surface. The first global, instantaneous representations of the two- and three-dimensional vortex structure will be attainable using recently developed techniques of high-image-density particle image velocimetry (HID-PIV). This approach will yield the space-time patterns of instantaneous vorticity and related topological features central to understanding the vortex development, vortex-vortex interactions, and vortex decay. Such an approach provides a physical basis for determining the classical turbulence statistics and mixing efficiency. A better understanding of the connection between vortex structure and bed scour and erosion can lead to new types of control techniques. In the near-field o f vortex development, small perturbations will substantially alter the initially-formed vortices and the rapidly developing three-dimensional vortex structure. In the far field, where the large-scale, quasi-two-dimensional vortical structures are expected to develop, control will take the form of spatial and temporal alterations of the bed friction and normal velocity at the bed; and localized generation of secondary concentrations of vorticity that may constructively or destructively interfere with the incident vortical structures. 2 1