Development of Measurement and Analysis System for 3-Dimensional Instantaneous Image of Turbulent Flows, and Application to Real River Flows.

1. 目标：在我们的环境中遇到的大多数流都是动荡的。湍流增强了动量和物质交换的能力。在河流流动中，它有助于增加泥沙物质的输送能力，河床和河岸的得分作用以及污染物的扩散。为了从根本上认识这些过程，对湍流的相干结构或大涡结构的研究是必不可少的。二十多年来，人们对这一问题进行了深入的研究。然而，大多数关于相干湍流的知识都是在小尺度的实验室实验和低雷诺数范围内获得的。这些研究的另一个缺陷是，结果是通过条件采样和集合平均技术推导出来的，由于平均的结果扭曲了湍流的真实图像。因此，本研究旨在(1)建立三维湍流瞬时图像的测量和分析系统，(2)将其应用于洪水期的实际河流流量。方法：(1)研制了多点测速仪器（风洞热线和小型电磁式测速仪，探头为5mmphi，长度为5cm，用于河流）。(2)利用有效的内外推法和MASCON方法建立了稀疏数据流场的逆估计，通过变分原理对原始的内外推数据进行了改进，使其满足连续性方程。结果：(1)利用稀疏测点同时获取的速度数据，利用MASCON方法可以重建大尺度湍流的瞬时图像。(2)该系统和方法已应用于风洞湍流研究和汛期河流研究（Himuma-gawa）。(3)低雷诺数范围湍流的相干结构在实际高雷诺数河流中得到了证实。然而，它在平均流向方面缺乏对称特征。(4)“沸腾”现象，即在洪水时期经常观察到的水面的近圆周剧烈运动，表明是由强烈的向上湍流引起的。少

1. Aims : Most flows encountered in our environments are turbulent. Turbulence augments the ability of momentum and material exchanges. In river flows, it contributes to increases in the transport capasity of sediment material, the action of scoring river beds and banks and the diffusivity of pollutants. In order to understand fundamentally these processes, the investigation of the coherent structure or large eddy structure of turbulence are indispendable. For more than two decades, the intensive researches have been performed on the problem. However, most of the knowledge on coherent turbulence has been obtained from small scale laboratory experiments and in the range of low Reynolds numbers. One of other defects of these researches is that the results have been deduced by the technique of conditional sampling and ensemble averages, which as a result of averaging distorts the real image of turbulence.Consequently, this research aims at (1) to establish the measurement and analysis sys … More tem of 3-dimensional instantaneous images of turbulence, and (2) apply them to a real river flow in flood periods.2. Method : (1) Multi-point velocity measurement instruments (hot-wires in wind tunnel and small scale electro-magnetic velocimeters (probe : 5 mmphi and 5cm length) in use for rivers) have been developed.(2) Inverse estimation of flow fields from sparse data has been established by application of an efficient inter- and extrapolation method and the MASCON method, which improves through the variational principle the raw inter- and extrapolated data to satisfy the continuity equation.3. Results : (1) From velosity data obtained simultaneously at sparselly positioned measuring points, the instantaneous image of large-scale turbulence can be reconstructed by the MASCON method.(2) The system and method has been applied to the turbulence research in a wind tunnel as well as a river flow in flood periods (Himuma-gawa).(3) The coherent structures of turbulence observed in low Reynolds number ranges have been confirmed in real river flows with high Reynolds numbers. However, it lacks a symmetric feature in terms of a mean flow direction.(4) The phenomenon of "Boil" which is a nearly circular violent motion of water surface observed frequently in flood periods in shown to be caused by a strong upward turbulence. Less