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Turbulent Structures and the Related Sediment Transport in Unsteady Open-Channel Flows

不稳定明渠流中的湍流结构及相关泥沙输运

基本信息

批准号：
06452273
负责人：
NEZU Iehisa
金额：
$ 4.03万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

In open-channel flows such as rivers and estuaries, various coherent vortices are often observed and greatly affect sediment transport. In the inner region which is very near the bed, bursting phenomena occur quasi-periodically and sustain the turbulence. On the other hand, in the outer region which is near the tree surface, a kolk-boil vortex occurs.There exists a strong upward-tilting streamwise vortex motion, called the "kolk" , near the bed, in a analogy to a tomado motion in the atmosphere, and the kolk vortex develops up to the free surface and then becomes a "boil". A typical boil starts life with high sediment concentration, as a raised circular or oval patch on the water surface ; in the course of time, it widens and gradually settles back down toward the river level until it subsides completely and merges with the surrounding, less-agitated parts. Such coherent vortices are generated especially in flood rivers.Therefore, it is very important to investigate unsteadiness effects on the turbulent structures and the coherent structures in unsteady open-channel flows so that the growing process of the dunes and the behavior of the suspended sediment can be explained dynamically. The authors have investigated turbulent structures in unsteady open-channel flows. It has been clarified that the unsteadiness has significant effects on the outer region near the free surface. The time variations of turbulent structure in the outer region and comparison with unsteady duct flow which has no free surface have examined.Furthermore, the detailed turbulent flow structures over the actual form of sand dunes were measured accurately by making use of two sets of fiber-optic laser Doppler anemometers (FLDA) and automatic traversing system. The three-dimensional structures of coherent vortices generated behind the dune crest and the reattachment point were measured accurately.

在河流、河口等明渠水流中，常常可以观察到各种相干涡旋，它们对泥沙输移有着重要的影响。在靠近床面的内部区域，准周期性地发生猝发现象，并维持湍流。另一方面，在靠近树面的外部区域，出现了一个kolk-boil涡，在床面附近存在一个强烈的向上倾斜的流向涡运动，称为“kolk”，类似于大气中的tomado运动，kolk涡发展到自由面，然后成为“boil”。一个典型的沸腾开始生活与高泥沙浓度，作为一个凸起的圆形或椭圆形的补丁在水面上;随着时间的推移，它扩大，并逐渐沉降回河平面，直到它完全消退，并与周围合并，不太激动的部分。因此，研究非定常性对明渠非定常流中湍流结构和拟序结构的影响，对于从动力学角度解释沙丘的发育过程和悬移质的运动规律具有重要意义。作者研究了明渠非定常流中的紊流结构。结果表明，非定常性对自由表面附近的外部区域有显著的影响。研究了沙丘外部湍流结构随时间的变化规律，并与无自由面的非定常管道流进行了比较，同时利用两套光纤激光多普勒风速仪（FLDA）和自动横移系统，精确测量了沙丘实际形态上的湍流结构。精确测量了沙丘顶部和再附着点后产生的相干涡的三维结构。