Coherent instability in wall-bounded shear
Coherent instability in wall-bounded shear
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壁限剪切的相干不稳定性
DOI：
10.1017/jfm.2018.202
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发表时间：
--
影响因子：
3.7
通讯作者：
M.J.P.
中科院分区：
文献类型：
--
作者：
M.J.P.
研究了壁面剪切流中相干发夹过程的机理。提出了一种基于形态学运算的流场结构识别与分析算法。该方法将流场的拓扑结构提取为离散数据集，并能够对多尺度的相干流过程进行时间分辨采样。在中等雷诺数的过渡和湍流边界层的直接模拟数据的应用揭示了发夹过程的流动物理。分析链接的发夹的指数不稳定性，这是放大的流向速度分量的负扰动扭曲的流。线性分析证实了与静脉曲张型无粘不稳定机制的联系。发夹包的形成与一个自相似过程有关，该过程起源于一片低速流体，并描述了导致形成单个发夹的动力学的重现。几千个湍流发夹的演变分析提供了一个统计特性的主要动力学，并产生一个时间分辨的平均发夹过程。与过渡发夹的比较表明定性一致的趋势，从而支持早期的假设，他们的等效性。就事件的因果关系而言，结果表明发夹是静脉曲张不稳定的表现，因此是血流主要扰动的结果而不是原因。
The mechanism underlying the coherent hairpin process in wall-bounded shear flows is studied. An algorithm for the identification and analysis of flow structures based on morphological operations is presented. The method distils the topology of the flow field into a discrete data set and enables the time-resolved sampling of coherent flow processes across multiple scales. Application to direct simulation data of transitional and turbulent boundary layers at moderate Reynolds number sheds light on the flow physics of the hairpin process. The analysis links the hairpin to an exponential instability which is amplified in the flow distorted by a negative perturbation in the streamwise velocity component. Linear analyses substantiate the connection to an inviscid instability mechanism of varicose type. The formation of packets of hairpins is related to a self-similar process which originates from a single patch of low-speed fluid and describes a recurrence of the dynamics that leads to the formation of an individual hairpin. Analysis of the evolution of several thousand turbulent hairpins provides a statistical characterization of the principal dynamics and yields a time-resolved average of the hairpin process. Comparisons with the transitional hairpin show qualitatively consistent trends and thus support earlier hypotheses of their equivalence. In terms of the causality of events, the results suggest that the hairpin is a manifestation of the varicose instability and as such is a consequence rather than a cause of the primary perturbations of the flow.
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影响因子：
3.7
作者：
M.J.P.
通讯作者：
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影响因子：
4.6
作者：
J. Jiménez
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DOI：
10.1615/tsfp6.190
发表时间：
2009
期刊：
Proceeding of Sixth International Symposium on Turbulence and Shear Flow Phenomena
影响因子：
--
作者：
G. Pujals;C. Cossu;S. Depardon
通讯作者：
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影响因子：
4.7
作者：
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影响因子：
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作者：
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通讯作者：
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