Study of the motion and interaction of micro-swimmers with different scales in Poiseuille flow

We conducted numerical simulations using the immersed boundary–lattice Boltzmann method to investigate the motion and interaction of microswimmers of different scales in Poiseuille flow. The squirmers self-propelling via generating surface waves were used as the model for microswimmers. The movement of two squirmers with different scale ratios (0.6–1.5), swimming Reynolds numbers (0.1–2.0), swimming strength (1–7), and blockage ratios (0.125–0.25) in Poiseuille flow was studied. Five classical motion patterns were identified: periodic tumbling, steady motion, periodic oscillation, damped oscillation, and chaotic motion modes. Initially, we examined the interaction between a pair of squirmers of the same scale and elucidated the causes of their different motion pattern transitions using the pressure distribution, direction angle, and swimming velocity of the squirmers. We investigated the variation of transport velocity with blockage ratio and swimming strength. A pair of squirmers with small ratios tended to migrate in a stable motion pattern, while those with large ratios showed a high tendency to change their motion patterns. Pushers with an increasing swimming Reynolds number were adsorbed to the wall and migrated stably along the wall.