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Turbulent Structure and Bursting Phenomena over Roughners Discontinuity

粗加工不连续性上的湍流结构和破裂现象

基本信息

批准号：
03805043
负责人：
NEZU Iehisa
金额：
$ 1.02万
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 (C)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-03805043/
关键词：
Turbulence Open Channel Roughners Bursting Burst LDA Shear Stress Roughners Discontinuity レ-ザ-流速計せん断応力

项目摘要

It is one of the most important topics in hydraulic engineering as well as in fluid mechanics to investigate experimentally the response of velocity distributions, bed shear stress and turbulence characteristics to abrupt changes of bed roughness in open-channel flows and also to predict such response functions by the use of a refined turbulence modeling.In contrast with boundary layers, researches on turbulent structures over roughness discontinuity in open-channel flows have recently been investigated by making use of hot-film anemometers and laser Doppler anemometer(LDA). For example, Nezu(1991) have conducted accurate velocity measurements over sand roughness discontinuity from smooth to rough beds and conversely rough to smooth beds, by the use of an LDA system. They examined the streamwise variations of mean velocity and bed shear stress. Of particular importance is the first observation of open-channel flows that the overshooting property associated with the smooth to rough bed change, and the downshooting property associated with the rough to smooth bed change occur immediately downstream of the roughness discontinuity.In the present study, accurate turbulence measurements over roughness discontinuity in open-channel flows have been furthermore carried out with a two-component LDA system in order to reveal such a notable overshooting property of bed shear stress and turbulence characteristics. The roughness conditions were varied more widely than those of Nezu(1991). Some numerical calculations were made then to predict the variation properties of velocity and turbulence profiles by making use of k-epsilon model.

通过实验研究明渠水流中流速分布、床面剪应力和湍动特性对床面粗糙度突变的响应，并利用改进的湍流模型预测这些响应函数，是水利工程和流体力学中的重要课题之一。与边界层相比，最近利用热膜风速仪和激光多普勒风速仪(LDA)研究了明渠水流中粗糙度不连续的湍流结构。例如，Nezu(1991)通过使用LDA系统对从光滑到粗糙的河床以及从粗糙到光滑的河床之间的沙质粗糙度不连续进行了精确的速度测量。他们研究了平均速度和床面剪切力的流向变化。特别重要的是首次对明渠水流进行了观测，发现与光滑到粗糙河床的变化相关的超调特性和与粗糙到光滑河床的变化相关的下冲特性发生在粗糙度不连续的下游。在本研究中，为了揭示明渠水流中这种显著的床面剪应力和湍流特性的超调特性，本研究进一步进行了明渠水流中粗糙度不连续的湍流测量。与Nezu(1991)相比，粗糙度条件的变化范围更广。在此基础上，利用k-epsilon模型进行了数值计算，预测了速度分布和湍流分布的变化特性。