Gilbert A D, Ogrin F Y, Petrov P G, Winlove C P
College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK.
Eur Phys J E Soft Matter. 2011 Nov;34(11):121. doi: 10.1140/epje/i2011-11121-9. Epub 2011 Nov 21.
This paper concerns the interaction of several ferromagnetic microswimmers, their motion and the resulting fluid mixing. Each swimmer consists of two ferromagnetic beads joined by an elastic link, and is driven by an external, time-dependent magnetic field. The external field provides a torque on a swimmer and, together with the varying attraction between the magnetic beads, generates a time-irreversible motion leading to persistent swimming in a low Reynolds number environment. The aim of the present paper is to consider the interactions between several swimmers. A regime is considered in which identical swimmers move in the same overall direction, and their motion is synchronised because of driving by the external field. It is found that two swimmers tend to encircle one another while three undergo more complicated motion that may involve the braiding of swimmer trajectories. By means of approximations it is established that the interaction between pairs of swimmers gives circulatory motion which falls off with an inverse square law and is linked to their overall speed of motion through the fluid. As groups of two or more swimmers move through the fluid they process fluid, leaving behind a trail of fluid that has undergone mixing: this is investigated by following streak lines numerically.
本文关注多个铁磁微泳体的相互作用、它们的运动以及由此产生的流体混合。每个泳体由通过弹性连杆连接的两个铁磁珠组成，并由外部随时间变化的磁场驱动。外部磁场对泳体施加一个转矩，并且与磁珠之间变化的吸引力一起，产生一种时间不可逆的运动，导致在低雷诺数环境中持续游动。本文的目的是考虑多个泳体之间的相互作用。研究了一种情形，即相同的泳体沿相同的总体方向移动，并且由于外部磁场的驱动它们的运动是同步的。发现两个泳体倾向于相互环绕，而三个泳体则经历更复杂的运动，这可能涉及泳体轨迹的编织。通过近似方法确定，成对泳体之间的相互作用产生循环运动，该运动以平方反比定律衰减，并且通过流体与它们的总体运动速度相关联。当两个或更多泳体的群体在流体中移动时，它们对流体进行处理，留下经过混合的流体轨迹：这通过数值跟踪纹线来进行研究。
