Varghese Minu, Baskaran Arvind, Hagan Michael F, Baskaran Aparna
Martin Fisher School of Physics, Brandeis University, Waltham, Massachusetts 02453, USA.
Phys Rev Lett. 2020 Dec 31;125(26):268003. doi: 10.1103/PhysRevLett.125.268003.
Two dimensional active fluids display a transition from turbulent to coherent flow upon decreasing the size of the confining geometry. A recent experiment suggests that the behavior in three dimensions is remarkably different; emergent flows transition from turbulence to coherence upon increasing the confinement height to match the width. Using a simple hydrodynamic model of a suspension of extensile rodlike units, we provide the theoretical explanation for this puzzling behavior. Furthermore, using extensive numerical simulations supported by theoretical arguments, we map out the conditions that lead to coherent flows and elucidate the critical role played by the aspect ratio of the confining channel. The mechanism that we identify applies to a large class of symmetries and propulsion mechanisms, leading to a unified set of design principles for self-pumping 3D active fluids.
二维活性流体在减小限制几何尺寸时会呈现从湍流到相干流的转变。最近的一项实验表明，三维情况下的行为显著不同；当增加限制高度以使其与宽度相匹配时，涌现流会从湍流转变为相干流。通过使用一个由可拉伸棒状单元组成的悬浮液的简单流体动力学模型，我们为这种令人困惑的行为提供了理论解释。此外，借助理论论证支持的广泛数值模拟，我们描绘出了导致相干流的条件，并阐明了限制通道纵横比所起的关键作用。我们所确定的机制适用于一大类对称性和推进机制，从而为自泵浦三维活性流体得出一套统一的设计原则。
