Alignment of vorticity and rods with Lagrangian fluid stretching in turbulence
Alignment of vorticity and rods with Lagrangian fluid stretching in turbulence
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DOI：
10.1017/jfm.2014.32
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发表时间：
2013-11
影响因子：
3.7
通讯作者：
R. Ni;N. Ouellette;G. Voth
中科院分区：
文献类型：
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作者：
R. Ni;N. Ouellette;G. Voth
摘要连续介质力学中的拉伸可以用柯西-格林应变张量来描述。这些张量量化了材料元素所经历的拉格朗日拉伸，并提供了一种强有力的方法来研究涉及拉伸的湍流流动过程，如涡旋拉伸和各向异性粒子的排列。通过对各向同性湍流模拟数据的分析，我们观察到棒状物和涡量之间的优先排列。我们表明，这种排列的出现是因为这两个量独立地倾向于与最强的拉格朗日伸展方向对准，正如左Cauchy-Green应变张量的最大本征向量所定义的那样。特别是，杆接近最强伸展方向的几乎完美的对准。涡度与拉伸的对准较弱，但仍比先前观测到的涡度与欧拉应变速率张量的特征向量的对准强得多。强涡度的排列与经历了相同拉伸的杆状排列几乎相同。
Abstract Stretching in continuum mechanics is naturally described using the Cauchy–Green strain tensors. These tensors quantify the Lagrangian stretching experienced by a material element, and provide a powerful way to study processes in turbulent fluid flows that involve stretching such as vortex stretching and alignment of anisotropic particles. Analysing data from a simulation of isotropic turbulence, we observe preferential alignment between rods and vorticity. We show that this alignment arises because both of these quantities independently tend to align with the strongest Lagrangian stretching direction, as defined by the maximum eigenvector of the left Cauchy–Green strain tensor. In particular, rods approach almost perfect alignment with the strongest stretching direction. The alignment of vorticity with stretching is weaker, but still much stronger than previously observed alignment of vorticity with the eigenvectors of the Eulerian strain rate tensor. The alignment of strong vorticity is almost the same as that of rods that have experienced the same stretching.