中国物理B ›› 2022, Vol. 31 ›› Issue (1): 14702-014702.doi: 10.1088/1674-1056/ac339a

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Speedup of self-propelled helical swimmers in a long cylindrical pipe

Ji Zhang(张骥)1, Kai Liu(刘凯)1, and Yang Ding(丁阳)1,2,†   

  1. 1 Beijing Computational Science Research Center, Beijing 100193, China;
    2 Beijing Normal University, Beijing 100875, China
  • 收稿日期:2021-09-13 修回日期:2021-10-14 接受日期:2021-10-27 出版日期:2021-12-03 发布日期:2021-12-18
  • 通讯作者: Yang Ding E-mail:dingyang@csrc.ac.cn

Speedup of self-propelled helical swimmers in a long cylindrical pipe

Ji Zhang(张骥)1, Kai Liu(刘凯)1, and Yang Ding(丁阳)1,2,†   

  1. 1 Beijing Computational Science Research Center, Beijing 100193, China;
    2 Beijing Normal University, Beijing 100875, China
  • Received:2021-09-13 Revised:2021-10-14 Accepted:2021-10-27 Online:2021-12-03 Published:2021-12-18
  • Contact: Yang Ding E-mail:dingyang@csrc.ac.cn

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摘要： Pipe-like confinements are ubiquitously encountered by microswimmers. Here we systematically study the ratio of the speeds of a force- and torque-free microswimmer swimming in the center of a cylindrical pipe to its speed in an unbounded fluid (speed ratio). Inspired by E. coli, the model swimmer consists of a cylindrical head and a double-helical tail connected to the head by a rotating virtual motor. The numerical simulation shows that depending on swimmer geometry, confinements can enhance or hinder the swimming speed, which is verified by Reynolds number matched experiments. We further developed a reduced model. The model shows that the swimmer with a moderately long, slender head and a moderately long tail experiences the greatest speed enhancement, whereas the theoretical speed ratio has no upper limit. The properties of the virtual motor also affect the speed ratio, namely, the constant-frequency motor generates a greater speed ratio compared to the constant-torque motor.

关键词: microswimmer, confinement, low Reynolds number, creeping flow

Abstract: Pipe-like confinements are ubiquitously encountered by microswimmers. Here we systematically study the ratio of the speeds of a force- and torque-free microswimmer swimming in the center of a cylindrical pipe to its speed in an unbounded fluid (speed ratio). Inspired by E. coli, the model swimmer consists of a cylindrical head and a double-helical tail connected to the head by a rotating virtual motor. The numerical simulation shows that depending on swimmer geometry, confinements can enhance or hinder the swimming speed, which is verified by Reynolds number matched experiments. We further developed a reduced model. The model shows that the swimmer with a moderately long, slender head and a moderately long tail experiences the greatest speed enhancement, whereas the theoretical speed ratio has no upper limit. The properties of the virtual motor also affect the speed ratio, namely, the constant-frequency motor generates a greater speed ratio compared to the constant-torque motor.

Key words: microswimmer, confinement, low Reynolds number, creeping flow

中图分类号:  (Low-Reynolds-number (creeping) flows)

  • 47.15.G
47.63.Gd (Swimming microorganisms) 87.17.Jj (Cell locomotion, chemotaxis) 87.16.Qp (Pseudopods, lamellipods, cilia, and flagella)