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水力发电学报

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明渠湍流速度的分形特征研究

  

  • 出版日期:2018-07-25 发布日期:2018-07-25

Fractal characteristics of turbulent flows in open channel

  • Online:2018-07-25 Published:2018-07-25

摘要: 湍流运动广泛存在于自然界的各种明渠水流中,了解湍流运动的速度特征对于指导工程实际问题如泥沙运动的规律、河流污染物的扩散、高速水流的脉动压强等具有十分重要的现实意义。采用明渠水槽去模拟湍流,利用ADV去测量各测线点的湍流流速,结合空间位置和小波理论,探究明渠断面湍流速度的分形特征。结果表明:湍流速度和及其经小波包多尺度分解的各个频段能量谱具有分形特征和自相似性,湍流空间流速分数维并不是某一个固定值,在空间范围内呈现一定波动的规律性,考虑雷诺数对湍流分数维的影响时,要具体对同一流态三个方向的湍流速度信号分别来探讨,低雷诺数下,湍流的分数维主要受到的是小尺度涡耗散影响。

Abstract: Turbulent motion exists widely in nature in a variety of open channel flows, and a good understanding of its velocity behaviors is practically of great significance helping solve the engineering problems related to sediment movement, pollutant diffusion in rivers, and fluctuating pressure in high-speed flows. This study conducts a flume experiment of the turbulent flows in an open channel using the ADV technique to measure turbulent velocities at the points of sampling lines, and adopts the wavelet theory to analyze the measurements and the characteristics of turbulence. Results show that fractal dimension and self-similarity feature the turbulent velocities measured and the energy spectrum on each band obtained through multi-scale wavelet packet decomposition, and that this fractal dimension is not a fixed value but varies in space with certain trends and volatility. When we consider the flow Reynolds number as a factor of the fractional dimension, the turbulence velocity signals of the same sampling point are discussed separately for each space direction. At low Reynolds numbers, the fractal dimensions depend mainly on the dissipation of small scale eddies.

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