Alignment of elongated swimmers in a laminar and turbulent Kolmogorov flow

Many aquatic microorganisms are able to swim. In natural environments they typically do so in the presence of flows. In recent years it has been shown that the interplay of swimming and flows can give rise to interesting and biologically relevant phenomena, such as accumulation of microorganisms in specific flow regions and local alignment with the flow properties. Here, we consider a mechanical model for elongated microswimmers in a Kolmogorov flow, a prototypic shear flow, both in steady and in turbulent conditions. By means of direct numerical simulations, supported by analytical calculation in a simplified stochastic setting, we find that the alignment of the swimming direction with the local velocity is a general phenomenon. We also explore how the accumulation of microorganisms, typically observed in steady flows, is modified by the presence of unsteady fluctuations.

Automated summary

In this article, the swimming behavior of aquatic microorganisms and their interaction with flows are studied. The results show that the alignment of the swimming direction with the local velocity is a general phenomenon in Kolmogorov flows. Additionally, the presence of unsteady fluctuations affects the accumulation behavior of microorganisms.