Coherent Structures and associated sediment transport in unsteady open-channel flows

在一些重要的课题中，紊流结构的非定常效应应予以考虑。在河流和河口等明渠流动中，经常观察到各种相干涡，它们对泥沙的输运有很大的影响。这些连贯的结构经常出现，特别是在洪水泛滥的河流中。在汛期的上升阶段和下降阶段，防洪结构的水动力特性有很大的不同。在上升阶段，由于上升阶段与沙丘的生长期相对应，并且与沙丘分离的涡在下一个沙丘上间歇性地碰撞并冲刷出周围的床质，因此由于克尔克沸腾涡的作用，悬沙浓度增加。本文研究了非定常明渠流和正弦波和沙丘床上的定常流的非定常和压力梯度对其相干结构的影响，以便从动力学角度解释沙丘的生长过程和悬沙的行为。特别地，通过同时使用两组LDA，精确地测量了沙丘上相干涡的具体三维行为。通过评价条件时空相关性，讨论了相干涡旋对流特性的差异。

There are some important topics in which the unsteadiness effects on turbulent structures should be considered. In open-channel flows such as rivers and estuaries, various coherent vortices are often observed and greatly affect sediment transport. These coherent structures often occur especially in flooded fluvial rivers. The hydrodynamic behavior of flood structures is quite different between the rising and falling stages of flood period. In the rising stage, the concentration of suspended sediment increases due to the kolk-boil vortex because the rising stage corresponds to thegrowing period of dunes and because separated vortex from the dune collides intermittently at the next dune and washes out bed materials around there.In this study, unsteadiness and pressure gradient effects on the coherent structures in unsteady open-channel flows and steady flows over sine-wave and dune beds, were investigated so that the growing process of the dunes and the behavior of the suspended sediment can be explained dynamically. Especially, the specific 3-D behaviors of coherent vortices over dunes were accurately measured by means of simultaneous use of two sets of LDA.The differences of convection properties on coherent vortices were discussed by evaluating the conditional space-time correlation.