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Open-Channel Turbulence Structure of Flow with Separation and Large Free-Surface Deformation

分离和大自由表面变形流动的明渠湍流结构

基本信息

批准号：
12650514
负责人：
FUJITA Ichiro
金额：
$ 0.38万
依托单位：
KOBE UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12650514/
关键词：
Open-channel turbulence Image analysis PIV Trench Hyudraulic jump Backward-facing step Flow separation Free surface 水面変動

项目摘要

Turbulence properties of an open-channel flow with a sudden change of bed elevation were experimentally investigated Using an image analysis method. In the present study, open-channel flows having a backward-facing step with or without a forward-facing step were treated. In the case with a forward-facing step, the elevation of the step was varied so that a non-symmetric concavity section was, formed in the middle of the channel, which we called a trench section. In the case of a single backward-facing step, turbulent flows with or without sand, roughness were investigated for comparison.In the trench case, it was found that an oscillatory hydraulic jump is generated within the trench section for a narrow range of the trench aspect ratio. In $he beginning, this phenomenon was considered as a result of the interaction between separation vortices from the upstream step and water surface. However, it was made clear that the periodic oscillation was caused by the imbalance between the mean velocity and the speed of wave created just downstream of the forward-facing step for a certain flow condition. The turbulence properties within the trench section were clarified using the image analysis ,techniques referred to as the Particle Tracking Velocimetry (PTV) and the Particle Image Velocimetry (PIV). A high-speed video camera and a high resolution video camera were utilized for these purposes. It was made clear that the increase of energy dissipation is closely related to the level of turbulence in the trench section. For the case of a backward-facing step, it was found that the reattachment length becomes about twenty percent shorter when the bed was roughened by sand elements, -which is a new finding never reported, elsewhere.

采用图像分析方法，对河床高程突变时明渠流动的湍流特性进行了实验研究。在本研究中，对有或没有前向台阶的后向台阶的明渠流动进行了处理。在朝向前方的台阶的情况下，台阶的高度发生了变化，因此在河道的中间形成了一个不对称的凹凸部分，我们称之为沟槽部分。在单个后向台阶的情况下，湍流有或没有沙子，粗糙度进行了比较研究。在沟槽情况下，发现在沟槽宽高比的窄范围内，沟槽段内产生振荡水力跳变。一开始，这种现象被认为是上游台阶分离涡与水面相互作用的结果。然而，明确了周期振荡是由于在一定的流动条件下，前台阶下游产生的平均速度与波速之间的不平衡造成的。利用图像分析技术，即粒子跟踪测速技术（PTV）和粒子图像测速技术（PIV），阐明了海沟剖面内的湍流特性。为此使用了高速摄像机和高分辨率摄像机。结果表明，能量耗散的增加与槽段湍流程度密切相关。对于面向后的台阶，人们发现，当床层被砂元素磨粗后，重新连接的长度缩短了大约20%，这是一个在其他地方从未报道过的新发现。