Hydrodynamic interactions of self-propelled swimmers
Hydrodynamic interactions of self-propelled swimmers
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DOI：
10.1039/c3sm00140g
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发表时间：
2013-01-01
期刊：
影响因子：
3.4
通讯作者：
Yamamoto, Ryoichi
中科院分区：
文献类型：
--
作者：
Molina, John J.;Nakayama, Yasuya;Yamamoto, Ryoichi
采用直接数值模拟方法研究了自推进颗粒悬浮液中的流体动力相互作用，该方法同时求解了宿主流体和游动颗粒。本文提出了一种改进的“光滑剖面”（SP）方法，将微泳者模拟为蠕动者，蠕动者是球形粒子，在粒子和流体之间具有特定的表面切向滑移速度。这个简化的游泳模型允许一个代表不同类型的推进（拉和推），因此是理想的研究游泳者之间的流体动力学相互作用。我们使用SP方法来研究由于粒子的游动运动而产生的扩散行为，并表明有两个基本机制负责这种现象：由粒子的蠕动运动引起的流体动力学相互作用，以及粒子-粒子碰撞。这种双重性质产生了两个不同的时间尺度和长度尺度，从而产生了两个扩散系数，这是我们通过对游泳运动进行适当的分析而获得的。我们发现，游泳者之间的碰撞可以解释在二元碰撞，其中有效的碰撞半径减少，由于在粘性流体中的游泳粒子的碰撞动力学。在短时间尺度下，游泳者的动力学类似于游泳悬浮液中的惰性示踪粒子的动力学，其中扩散运动由流体-粒子碰撞引起。我们的研究结果，沿着我们所介绍的模拟方法，将使我们能够更好地了解复杂的水动力相互作用的自推进游泳。
The hydrodynamic interactions of a suspension of self-propelled particles are studied using a direct numerical simulation method which simultaneously solves for the host fluid and the swimming particles. A modified version of the "Smoothed Profile" (SP) method is developed to simulate microswimmers as squirmers, which are spherical particles with a specified surface-tangential slip velocity between the particles and the fluid. This simplified swimming model allows one to represent different types of propulsion (pullers and pushers) and is thus ideal to study the hydrodynamic interactions among swimmers. We use the SP method to study the diffusive behavior which arises due to the swimming motion of the particles, and show that there are two basic mechanisms responsible for this phenomena: the hydrodynamic interactions caused by the squirming motion of the particles, and the particle-particle collisions. This dual nature gives rise to two distinct time- and length-scales, and thus to two diffusion coefficients, which we obtain by a suitable analysis of the swimming motion. We show that the collisions between swimmers can be interpreted in terms of binary collisions, in which the effective collision radius is reduced due to the collision dynamics of swimming particles in viscous fluids. At short time-scales, the dynamics of the swimmer is analogous to that of an inert tracer particle in a swimming suspension, in which the diffusive motion is caused by fluid-particle collisions. Our results, along with the simulation method we have introduced, will allow us to gain a better understanding of the complex hydrodynamic interactions of self-propelled swimmers.