Confinement induced three-dimensional trajectories of microswimmers in rectangular channels

Using lattice Boltzmann simulations and an analytical framework based on far-field approximations and method of images, we study the trajectories of microswimmers inside three-dimensional channels of square and rectangular cross-sections. We find that pusher-type microswimmers move helically inside the square tube, weak pullers slide through the center of the channel while strong pullers exhibit a trajectory which is off-center. The trajectories of the neutral swimmers are challenging to generalize due to the sensitivity to the initial conditions. Finally a method of superposition is used to construct three dimensional trajectories, thus explaining the origin of their apparent complexity.