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动都是湍流的。湍流增强了动量和物质交换的能力。在河流水流中，它有助于增加泥沙物质的输送能力、河床和堤岸的冲刷作用以及污染物的扩散性。为了从根本上理解这些过程，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从小规模的实验室实验中获得的，并且是在低雷诺数范围内获得的。这些研究的另一个缺陷是结果是采用条件采样和集合平均技术推导出来的，平均的结果扭曲了真实的湍流图像。因此，本研究的目的是：(1)建立…测量和分析系统更多的湍流三维瞬时图像，以及(2)将它们应用于洪水期间的真实河流流动。方法：(1)研制了多点测速仪器(风洞热线和河流用小型电磁测速仪(探头长度分别为5 mm和5 cm))。(2)应用一种有效的内、外推法和mascon法，利用变分原理对原始内、外推数据进行改进，使其满足连续性方程，实现了稀疏数据的反推。结果：(1)由稀疏测点同时获得的流速数据，可以用Mascon方法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洪水期河流(Himuma-gawa)的湍流研究。(3)在高雷诺数的真实河流中，证实了在低雷诺数范围内观测到的湍流的相干结构。但在平均流向上缺乏对称性。(4)“沸腾”现象是洪水期经常出现的一种近圆形的水面剧烈运动，它是由一股强烈的向上湍流引起的。较少

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