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The effects of conditions at open-channel bed or side shape on the two-dimensional water-surface variations

明渠河床条件或边形对二维水面变化的影响

基本信息

批准号：
17560459
负责人：
FUJITA Ichiro
金额：
$ 1.28万
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：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-17560459/
关键词：
Open-channel turbulence Image analysis CFD water-surface variation roughness turbulence side cavity flow 可視化計測 LES

项目摘要

In this project, investigations based on hydraulic experiments and numerical simulations are performed in order to examine the effects of the conditions at open-channel bed or side shapes on the water surface variation and oscillation.Regarding the channel bed effects, strip roughness boundaries with various spacing are generated at the channel bottom and hydraulic experiments are conducted with a wide range of the Froude number. Image analysis methods based on the PIV technique are used to analyze the two-dimensional velocity field in the vertical cross section. It was made clear that the deformation of water surface becomes more evident as the increase of the Froude number and the change in the water surface variation is closely related to the generation of the large-scale vertical region near the bottom between the strip roughnesses. The numerical simulation with LES is also performed for a relatively small Froude number, with a result that some of the separated vortices generated at a strip roughness ascend up to the water surface as a boil vortex producing positive divergence field at the water surface. The three-dimensional vortex structure is also revealed from the LES analysis.As for the effects of the side channel shape, a rectangular side cavity with various aspect ratios is attached at a straight open-channel and the two-dimensional water surface oscillation is measured using a stereoscopic image analysis system composed of two high speed-video cameras. The measurement results are analyzed with POD technique in order to detect the fundamental feature of the flow. It was made clear that the surface oscillation mode changes drastically with a change in the aspect ratio of the side cavity. In addition, the three-dimensional flow structure at the side cavity is revealed using a LES simulation that takes into account of the change in the water surface level.

本项目通过水力学试验和数值模拟研究，探讨了明渠河床条件和侧边形状对水面变化和振荡的影响。在河床影响方面，在河床底部设置了不同间距的条形粗糙边界，并在较宽的弗劳德数范围内进行了水力学试验。采用基于PIV技术的图像分析方法，对垂直截面上的二维速度场进行了分析。研究表明，随着弗劳德数的增大，水面变形更加明显，水面变化的变化与条形粗糙面之间近底大尺度垂向区的产生密切相关。在较小的Froude数条件下进行了大涡模拟，结果表明，在粗糙度为100 °时，部分分离涡上升到水面，形成沸腾涡，在水面产生正的辐散场。对于侧槽形状的影响，在直明渠上附加不同长宽比的矩形侧腔，利用由两台高速摄像机组成的立体图像分析系统测量了二维水面振荡。利用POD技术对测量结果进行了分析，以检测流动的基本特征。很明显，表面振荡模式随着侧腔的纵横比的变化而急剧变化。此外，在侧腔的三维流动结构揭示了使用LES模拟，考虑到在水面高度的变化。