Multifractal characteristics of the jet turbulent intensity depending on the outfall nozzle geometry
Multifractal characteristics of the jet turbulent intensity depending on the outfall nozzle geometry
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取决于出口喷嘴几何形状的射流湍流强度的多重分形特征
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
S. Lyu
中科院分区：
文献类型：
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作者：
Y. Seo;S. Lyu
多重分形度使得能够检查在一个域上分布的量的特征。用粒子图像测速仪研究了三种喷嘴几何形状的速度场和湍流特性，研究了射流实验获得的湍流强度的多重分形特性。实验结果表明，根据喷嘴几何形状的不同，湍流强度的分布和由此产生的稀释表现出不同的行为。实验还表明，不同形状的排水口的横向速度分布是相似的，同时也证明了传统的相似假设。在二维空间中，用Box Count方法得到了湍流强度的多重分形指数。结果表明，在二维空间中得到的湍流强度具有共同的多重分形谱，而在同一空间中观测到的速度或剪应力则不是这样。尽管横向流速分布相似，但多重分维指数明显地表现出不同的排水口几何形状。特别是，随着湍流强度和稀释度的增加，最小的Lipschitz-Hölder指数(αmin)和熵维(α1)有增大的趋势。这些结果表明，多重分维特性可以潜在地用于根据所产生的稀释来分类和评价排污口的能力。
The multifractal measure enables an examination of the characteristics of a quantity distributed over a domain. This study examined the multifractal properties of turbulent intensities obtained from jet discharge experiments, where three types of nozzle geometries were examined in terms of the velocity fields and turbulent characteristics using particle image velocimetry. Depending on the nozzle geometry, the experimental results showed that the distribution of turbulent intensities and resulting dilution exhibited different behaviors. The experiment also showed that the transversal velocity profiles are similar to each other regardless of the outfall nozzle shapes and demonstrates the traditional similarity assumption at the same time. The multifractal exponents of the turbulent intensities were obtained with Box Count Method in a two-dimensional space. The results showed that the turbulent intensities obtained in two-dimensional space have a common multifractal spectrum, which was not the case for the velocity or shear stress observed in the same space. Although the transversal velocity profiles are similar, the multifractal exponent clearly shows a difference depending on the outfall geometries. In particular, the minimum value of the Lipschitz–Hölder exponent (αmin) and the entropy dimension (α1) tends to increase as turbulent intensity and dilution increase. These results suggest that the multifractal properties can be utilized potentially to categorize and evaluate the discharge outfall capabilities in terms of the resulting dilution.