The Dynamics of Bursting Process and Secondary Currents in River Turbulence'

理解复杂的物理现象是计算物理学的一个重要主题。尤其是湍流，是当今最有趣的研究课题之一，受到了众多研究人员和工程师的热切关注。在这种情况的背景下，人们发现，尽管湍流具有随机性质，但它具有连贯的结构，并且可以通过纳维尔-斯托克斯方程来确定地估计。基于计算流体力学的方法已经增加了对湍流的理解。特别是，一种称为域名系统的方法由于其高精度而发挥着更大的作用。由于它只基于物理定律，而没有湍流模型，因此它有望普遍适用于任何流场。然而，如谱方法，不适用于复杂的边界流，而适用性是从工程角度要求的。使用有限差分方法的dns方法最近由于其可扩展到…而不断增加。越来越多的计算机系统。然而，仍然只对包括槽道流动在内的简化湍流场进行了分析。关于具有曲线边界的一般流场的报道很少(Krettenauer等人，1992，de Angelis等人，1997，Mito等人，1998，Ohta等人，1998)。与此同时，流动可视化技术的发展揭示了复杂时空结构的湍流中存在着相对长寿命的相干结构(Kline等人，1967)，并已经证明了相干结构与涉及湍流的产生、混合和扩散的湍流传输密切相关。这种拟序结构形成了一个被螺旋流包围的细长圆柱形高涡区域，称为圆柱形螺旋涡(低压涡)。它在壁面附近产生条纹和雷诺剪应力方面起着重要作用，因此被认为是表达湍流结构的基本结构。然而，需要澄清的还有很多，包括与普兰特第二类次级洋流的关系。因此，对粒子图像测速技术(PIV)的未来发展寄予了期望。了解湍流结构不仅需要时间平均场和瞬时场的数据，而且还需要关于流场不断变化的时间发展的信息。因此，目前，包括数值分析在内的数值分析被认为是非常有效的方法。较少

Understanding complicated physical phenomena is a major theme of computational physics. Especially, turbulent flows are one of the most interesting subjects, and have been studied energetically by many researchers and engineers. In the background of the situation is the finding that turbulence, although of a random nature, has a coherent structure, and can be estimated deterministically by a Navier-Stokes equation. Approaches based on computational fluid dynamics have already increased the understanding of turbulent flows. In particular, a method called DNS plays a greater role owing to its high accuracy. Since it is based only on physical laws without a turbulence model, DNS is expected to be universally applicable to any flow field. DNS such as the spectral method, however, is not applicable to complex boundary flows while the applicability is required from an engineering viewpoint. DNS methods using a finite difierence method have recently been increasing due to their expasibility t … More o more comptex systems. Analyses have, however, still been made only of simplified turbulence fields including channel flows. Few reports are available on general flow fields with a curvilinear boundary(Krettenauer et al.,1992, De Angelis et al.,1997, Mito et al., 1998,Ohta et al.,1998).Technological development for flow visualization, in the meantime, has revealed the existence of a coherent structure of relatively long life in turbulent flows of a complex time-space structure(Kline et al.,1967), and has also been demonstrating that the coherent structure is closely related to the transport of turbulent flows involving the generation, mixing and diffusion of turbulence. The coherent structure forms a slender cylindrical high-vorticity area surrounded by spiral flows, and is called cylindrical spiral vortex(low-pressure vortex). It plays a important role in generating streaks and Reynolds shear stress near the wall, and is thus regarded as a basic structure that expresses the turbulence structure. Much, however, needs to be clarified including the relationship to the secondary currents of Prandtl's second kind. Expectations are, therefore, placed on future development in particle-image velocimetry(PIV). Understanding the turbulence structure requires not only the data on the time-average and instantaneous fields but also information on ever-changing time development of the flow field. At present, therefore, numerical analyses including DNS are considered highly effective methods. Less