中国物理B ›› 2023, Vol. 32 ›› Issue (11): 114704-114704.doi: 10.1088/1674-1056/acea6d

所属专题: SPECIAL TOPIC — Celebrating the 100th Anniversary of Physics Discipline of Northwest University

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Bacterial turbulence in gradient confinement

Ningzhe Yan(颜宁哲), Chenliang Xie(谢晨亮), Hao Luo(罗昊), Yanan Liu(刘亚楠), and Guangyin Jing(经光银)   

  1. School of Physics, Northwest University, Xi'an 710127, China
  • 收稿日期:2023-06-09 修回日期:2023-07-12 接受日期:2023-07-26 出版日期:2023-10-16 发布日期:2023-11-03
  • 通讯作者: Yanan Liu, Guangyin Jing E-mail:yanan.liu@nwu.edu.cn;jing@nwu.edu.cn
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 12174306 and 12004308) and the Natural Science Basic Research Program of Shaanxi (Grant No. 2023-JC-JQ-02). The authors also thank D. Saintillan, A. Lindner, and X. Shi for useful discussions and contributive suggestions.

Bacterial turbulence in gradient confinement

Ningzhe Yan(颜宁哲), Chenliang Xie(谢晨亮), Hao Luo(罗昊), Yanan Liu(刘亚楠), and Guangyin Jing(经光银)   

  1. School of Physics, Northwest University, Xi'an 710127, China
  • Received:2023-06-09 Revised:2023-07-12 Accepted:2023-07-26 Online:2023-10-16 Published:2023-11-03
  • Contact: Yanan Liu, Guangyin Jing E-mail:yanan.liu@nwu.edu.cn;jing@nwu.edu.cn
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 12174306 and 12004308) and the Natural Science Basic Research Program of Shaanxi (Grant No. 2023-JC-JQ-02). The authors also thank D. Saintillan, A. Lindner, and X. Shi for useful discussions and contributive suggestions.

摘要: We investigate a novel form of non-uniform living turbulence at an extremely low Reynolds number using a bacterial suspension confined within a sessile droplet. This turbulence differs from homogeneous active turbulences in two or three-dimensional geometries. The heterogeneity arises from a gradient of bacterial activity due to oxygen depletion along the droplet's radial direction. Motile bacteria inject energy at individual scales, resulting in local anisotropic energy fluctuations that collectively give rise to isotropic turbulence. We find that the total kinetic energy and enstrophy decrease as distance from the drop contact line increases, due to the weakening of bacterial activity caused by oxygen depletion. While the balance between kinetic energy and enstrophy establishes a characteristic vortex scale depending on the contact angle of the sessile drop. The energy spectrum exhibits diverse scaling behaviors at large wavenumber, ranging from k-1/5 to k-1, depending on the geometric confinement. Our findings demonstrate how spatial regulation of turbulence can be achieved by tuning the activity of driving units, offering insights into the dynamic behavior of living systems and the potential for controlling turbulence through gradient confinements.

关键词: collective motion, bacterial turbulence, bacterial drop, gradient confinement

Abstract: We investigate a novel form of non-uniform living turbulence at an extremely low Reynolds number using a bacterial suspension confined within a sessile droplet. This turbulence differs from homogeneous active turbulences in two or three-dimensional geometries. The heterogeneity arises from a gradient of bacterial activity due to oxygen depletion along the droplet's radial direction. Motile bacteria inject energy at individual scales, resulting in local anisotropic energy fluctuations that collectively give rise to isotropic turbulence. We find that the total kinetic energy and enstrophy decrease as distance from the drop contact line increases, due to the weakening of bacterial activity caused by oxygen depletion. While the balance between kinetic energy and enstrophy establishes a characteristic vortex scale depending on the contact angle of the sessile drop. The energy spectrum exhibits diverse scaling behaviors at large wavenumber, ranging from k-1/5 to k-1, depending on the geometric confinement. Our findings demonstrate how spatial regulation of turbulence can be achieved by tuning the activity of driving units, offering insights into the dynamic behavior of living systems and the potential for controlling turbulence through gradient confinements.

Key words: collective motion, bacterial turbulence, bacterial drop, gradient confinement

中图分类号:  (Micro- and nano- scale flow phenomena)

  • 47.61.-k
47.63.-b (Biological fluid dynamics) 47.63.Gd (Swimming microorganisms) 47.90.+a (Other topics in fluid dynamics)