The dynamics of swimmers in vortex-dominated flows: the role of rotational noise

We use dynamical systems techniques to study the transport of swimming microorganisms, such as the marine algae tetraselmis, in vortex-dominated, two-dimensional flows. In particular, we analyze so-called "invariant tori" in phase space that result in tubes generating long-range ballistic transport along the separatrices between vortices. Particular attention is focused on the impact of rotational stochasticity on the robustness of these tori. We first extract a noise model directly from experimental trajectories of algae in a laboratory sheer flow. This model turns out to be non-Gaussian, with a Lorentzian probability distribution. This rotational noise is then combined with the deterministic swimmer dynamics. The impact of noise on the root-mean-square and maximum distance attained is studied as a function of swimmer shape and swimming speed.