Cascade leading to the emergence of small structures in vortex ring collisions
Cascade leading to the emergence of small structures in vortex ring collisions
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DOI：
10.1103/physrevfluids.3.124702
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发表时间：
2018-12-17
影响因子：
2.7
通讯作者：
Rubinstein, Shmuel M.
中科院分区：
文献类型：
--
作者：
McKeown, Ryan;Ostilla-Monico, Rodolfo;Rubinstein, Shmuel M.
当涡环以足够高的雷诺数迎头相撞时，它们最终会通过激烈的相互作用而湮灭，从而将其核心分解成一团湍急的云。我们的实验表明，这种非常强的相互作用，导致在非常精细的尺度上产生流体运动，揭示了大量流体中不稳定的迭代级联的直接证据。当相干涡核相互靠近时，它们变形成帐篷状结构，相互应变导致它们局部扁平成极薄的涡片。然后，这些薄片分解成更小的次级涡旋细丝，这些细丝本身迅速变平，并分解成更小的第三级细丝。通过对完整的Navier-Stokes方程进行数值模拟，我们还解决了这种不稳定性的一次迭代，并强调了粘性在涡旋层破裂中所起的微妙作用。这种在不同尺度上观察到的不稳定迭代级联与最近的理论预测的一致，可以提供一个机制框架，在其中可以将湍流的演变作为一系列离散的动态不稳定来实时检查。
When vortex rings collide head-on at high enough Reynolds numbers, they ultimately annihilate through a violent interaction which breaks down their cores into a turbulent cloud. We experimentally show that this very strong interaction, which leads to the production of fluid motion at very fine scales, uncovers direct evidence of an iterative cascade of instabilities in a bulk fluid. When the coherent vortex cores approach each other, they deform into tentlike structures and the mutual strain causes them to locally flatten into extremely thin vortex sheets. These sheets then break down into smaller secondary vortex filaments, which themselves rapidly flatten and break down into even smaller tertiary filaments. By performing numerical simulations of the full Navier-Stokes equations, we also resolve one iteration of this instability and highlight the subtle role that viscosity must play in the rupturing of a vortex sheet. The concurrence of this observed iterative cascade of instabilities over various scales with those of recent theoretical predictions could provide a mechanistic framework in which the evolution of turbulent flows can be examined in real time as a series of discrete dynamic instabilities.