Detection of Lagrangian coherent structures in three-dimensional turbulence
Detection of Lagrangian coherent structures in three-dimensional turbulence
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DOI：
10.1017/s0022112006003648
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发表时间：
2007-02-10
影响因子：
3.7
通讯作者：
Haller, G.
中科院分区：
文献类型：
--
作者：
Green, M. A.;Rowley, C. W.;Haller, G.
我们使用直接李雅普诺夫指数（DLE），以确定拉格朗日相干结构在两个不同的三维流动，包括一个单独的发夹涡，和一个充分发展的湍流。这些结果进行了比较，常用的欧拉标准相干涡。我们发现，尽管额外的计算成本，DLE方法有几个优点，欧拉方法，包括更多的细节和能力，定义结构边界，而不依赖于一个预先选定的阈值。作为另一个优点，DLE方法不需要速度导数，这通常是太嘈杂的湍流的研究中是有用的。我们研究了一个单一的发夹涡到一个类似的结构包的演变，并表明，一个二次涡的诞生对应于拉格朗日相干结构的双曲性的损失。
We use direct Lyapunov exponents (DLE) to identify Lagrangian coherent structures in two different three-dimensional flows, including a single isolated hairpin vortex, and a fully developed turbulent flow. These results are compared with commonly used Eulerian criteria for coherent vortices. We find that, despite additional computational cost, the DLE method has several advantages over Eulerian methods, including greater detail and the ability to define structure boundaries without relying on a preselected threshold. As a further advantage, the DLE method requires no velocity derivatives, which are often too noisy to be useful in the study of a turbulent flow. We study the evolution of a single hairpin vortex into a packet of similar structures, and show that the birth of a secondary vortex corresponds to a loss of hyperbolicity of the Lagrangian coherent structures.