EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Accumulation and alignment of elongated gyrotactic swimmers in turbulence

Linfeng Jiang1, Zehua Liu2, and Chao Sun1,2
Linfeng Jiang et al.
  • 1Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing, China
  • 2Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing, China

Understanding the dynamics and transport of elongated gyrotactic swimmers in a flow is essential for the ecology of aquatic plankton. We study their dynamics in turbulence, whose orientation is governed by gravitational torque and local fluid velocity gradient. The gyrotaxis strength is measured by the ratio of the Kolmogorov time scale to the reorientation time scale due to gravity, and a large value of this ratio means the gyrotaxis is strong. By means of direct numerical simulations, we investigate the effects of swimming velocity and gyrotactic stability on spatial accumulation and alignment. Three-dimensional Voronoi analysis is used to study the spatial distribution and time evolution of the particle concentration. We study spatial distribution by examing the overall preferential sampling and where clusters and voids (subsets of particles that have small and large Voronoi volumes respectively) form. Compared with the ensemble particles, the preferential sampling of clusters and voids is found to be more pronounced. The clustering of fast swimmers lasts much longer than slower swimmers when the gyrotaxis is strong and intermediate, but an opposite trend emerges when the gyrotaxis is weak. In addition, we study the preferential alignment with the Lagrangian stretching direction, with which passive slender rods have been known to align. We show that the Lagrangian alignment is reduced by the swimming velocity when the gyrotaxis is weak, while the Lagrangian alignment is enhanced for the regime in which gyrotaxis is strong.

How to cite: Jiang, L., Liu, Z., and Sun, C.: Accumulation and alignment of elongated gyrotactic swimmers in turbulence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2386,, 2022.