  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.
