微流控混沌流中初速度对色散的作用
On the role of initial velocities in pair dispersion in a microfluidic chaotic flow
摘要：
混沌流驱动流体的混合和有效传输，以及我们从日常生活经验中熟悉的相关美丽复杂模式。从理论和工程的角度来看，在小尺度下产生这种流动是非常具有挑战性的。这可以通过引入极少量的长柔性聚合物来克服，从而产生称为\textit{elastic turbulence}的混沌流。其研究的理论框架的基础在于一个空间平滑和随机的时间速度场的假设。以前对弹性湍流的测量仅限于二维。使用一种新的三维粒子跟踪方法，我们进行了微流控实验，使我们能够探索弹性湍流的角度来看，颗粒随流动。我们的研究结果表明，平滑假设已经打破规模小于十分之一的系统大小。此外，我们提供了确凿的实验证据表明，\textit{ballistic}分离盛行的动力学对示踪剂在很长的时间和距离，表现出记忆的初始分离速度。弹道弥散具有普遍性，但在小尺度混沌流中却一直被忽视。
英文摘要：
Chaotic flows drive mixing and efficient transport in fluids, as well as the associated beautiful complex patterns familiar to us from our every day life experience. Generating such flows at small scales where viscosity takes over is highly challenging from both the theoretical and engineering perspectives. This can be overcome by introducing a minuscule amount of long flexible polymers, resulting in a chaotic flow dubbed \textit{elastic turbulence}. At the basis of the theoretical frameworks for its study lie the assumptions of a spatially smooth and random-in-time velocity field. Previous measurements of elastic turbulence have been limited to two-dimensions. Using a novel three-dimensional particle tracking method, we conduct a microfluidic experiment, allowing us to explore elastic turbulence from the perspective of particles moving with the flow. Our findings show that the smoothness assumption breaks already at scales smaller than a tenth of the system size. Moreover, we provide conclusive experimental evidence that \textit{ballistic} separation prevails in the dynamics of pairs of tracers over long times and distances, exhibiting a memory of the initial separation velocities. The ballistic dispersion is universal, yet it has been overlooked so far in the context of small scales chaotic flows.
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