The motion of swimming microbes in time-periodic flows

We present experiments on the motion of swimming Euglena algae microbes in a time-periodic, oscillating vortex array flow. Previous experiments on swimming microbes in a time-independent vortex chain flow demonstrated the existence of swimming invariant manifolds (SwIMs) that act as one-way barriers that impede the motion of the microbes in the flow. The SwIMs also were found to combine to form “chutes” that explain transport of swimmers between adjacent vortices. We examine how these manifolds and chutes are affected by time-dependent perturbations and how these modifications change the nature of the SwIMs as barriers and change the way in which swimming microbes cross between vortices in the flow.