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Emergent collective dynamics of bottom-heavy squirmers under gravity.
The European Physical Journal E ( IF 1.8 ) Pub Date : 2020-05-25 , DOI: 10.1140/epje/i2020-11949-8
Felix Rühle 1 , Holger Stark 1
Affiliation  

Abstract.

We present the results of hydrodynamic simulations using the method of multi-particle collision dynamics for a system of squirmer microswimmers moving under the influence of gravity at low Reynolds numbers. In addition, the squirmers are bottom-heavy so that they experience a torque which aligns them along the vertical. The squirmers interact hydrodynamically by the flow fields of a stokeslet and rotlet, which are initiated by the acting gravitational force and torque, respectively, and by their own flow fields. By varying the ratio of swimming to bulk sedimentation velocity and the torque, we determine state diagrams for the emergent collective dynamics of neutral squirmers as well as strong pushers and pullers. For low swimming velocity and torque we observe conventional sedimentation, while the sedimentation profile becomes inverted when their values are increased. For neutral squirmers we discover convective rolls of circulating squirmers between both sedimentation states, which sit at the bottom of the system and are fed by plumes made of collectively sinking squirmers. At larger torques porous clusters occur that spawn single squirmers. The two latter states can also occur transiently starting from a uniform squirmer distribution and then disappear in the long-time limit. For strong pushers and pullers only weak plume formation is observed.

Graphical abstract



中文翻译:

重力作用下重底松鼠的新兴集体动力学。

摘要。

我们提出了使用多粒子碰撞动力学方法在低雷诺数下在重力影响下运动的旋风微泳者系统进行流体动力学模拟的结果。另外,鞘管底部较重,因此它们承受的扭矩使它们沿垂直方向对齐。鞘管通过斯托克斯小流和小rotlet的流场进行流体动力相互作用,它们分别由作用的重力和转矩以及它们自己的流场引发。通过改变游动比与总体沉降速度和扭矩的比率,我们确定了中性松鼠以及强力推动者和拉拔者出现的集体动力的状态图。对于低游泳速度和扭矩,我们会观察到常规的沉降,当它们的值增加时,沉积剖面变得相反。对于中性松鼠,我们发现两种沉积状态之间的循环松鼠的对流辊位于系统的底部,并由集体下沉的松鼠组成的羽流喂养。在更大的扭矩下,会出现多孔团簇,这些团簇会产生单个松鼠。后两个状态也可以从均匀的鼠形分布开始瞬时出现,然后在长时间限制内消失。对于强力推动器和拉拔器,只能观察到较弱的羽流形成。在更大的扭矩下,会出现多孔团簇,这些团簇会产生单个松鼠。后两个状态也可以从均匀的鼠形分布开始瞬时出现,然后在长时间限制内消失。对于强力推动器和拉拔器,只能观察到较弱的羽流形成。在更大的扭矩下,会出现多孔团簇,这些团簇会产生单个松鼠。后两个状态也可以从均匀的鼠形分布开始瞬时出现,然后在长时间限制内消失。对于强力推动器和拉拔器,只能观察到较弱的羽流形成。

图形概要

更新日期:2020-05-25
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