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arXiv 2104.08951physics.flu-dyn
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二维弹性turbulence的统计性质

Statistical properties of two-dimensional elastic turbulence

Himani Garg, Enrico Calzavarini, Stefano Berti

摘要:

我们数值研究了弹性湍流区聚合物稀溶液的空间和时间统计特性,即,在雷诺数为零和高Weissenberg数时出现的混沌流态。我们的目的是阐明在空间域中进行的流动性质的测量与在时间域中采取的测量之间的关系,这是解释弹性湍流实验结果的关键点,并讨论泰勒假设的有效性。为此,我们进行了广泛的直接数值模拟的二维Kolmogorov流的Oldrophil-B粘弹性流体。静态点状数值探针被放置在流中的不同位置,特别是在平均流振幅的极值处。在充分发展的弹性湍流制度的结果显示大的速度波动,相比的平均流量,导致泰勒的冻结场假设的部分故障。而二阶统计,探测光谱和结构函数,在空间和时间域中显示一致的缩放行为,三阶统计突出强大的差异。特别是时间分析未能捕获流向纵向速度增量的偏斜度。最后,我们评估作为尺度函数的湍流波动的统计不均匀性和各向同性的程度。虽然该系统是只有弱非均匀的横流方向,它被发现是高度各向异性在所有尺度。

英文摘要:

We numerically investigate the spatial and temporal statistical properties of a dilute polymer solution in the elastic turbulence regime, i.e., in the chaotic flow state occurring at vanishing Reynolds and high Weissenberg numbers. We aim at elucidating the relations between measurements of flow properties performed in the spatial domain with the ones taken in the temporal domain, which is a key point for the interpretation of experimental results on elastic turbulence and to discuss the validity of Taylor's hypothesis. To this end, we carry out extensive direct numerical simulations of the two-dimensional Kolmogorov flow of an Oldroyd-B viscoelastic fluid. Static point-like numerical probes are placed at different locations in the flow, particularly at the extrema of mean flow amplitude. The results in the fully developed elastic turbulence regime reveal large velocity fluctuations, as compared to the mean flow, leading to a partial breakdown of Taylor's frozen-field hypothesis. While second-order statistics, probed by spectra and structure functions, display consistent scaling behaviors in the spatial and temporal domains, the third-order statistics highlight robust differences. In particular the temporal analysis fails to capture the skewness of streamwise longitudinal velocity increments. Finally, we assess both the degree of statistical inhomogeneity and isotropy of the flow turbulent fluctuations as a function of scale. While the system is only weakly non-homogenous in the cross-stream direction, it is found to be highly anisotropic at all scales.

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