Dynamics of a spheroidal squirmer interacting with a cylindrical obstacle.

Microorganisms or man-made microswimmers swimming near obstacles have been investigated intensively owing to their importance in biology, physiology, and biomedical engineering. In this work, a direct-forcing fictitious domain method is employed to numerically investigate the interaction between a prolate microorganism (modeled as a squirmer) and a cylindrical obstacle. We report four distinct types of swimming trajectories-forward orbiting, backward orbiting, hovering, and scattering depending on swimmer's aspect ratio. The results illustrate that strong pushers prefer a forward orbit with a low obstacle curvature and a high aspect ratio, while a backward orbit is favored for small aspect ratios. But spheroidal pullers generally scatter off the obstacle. We observe a 'hovering' mode between the backward orbiting and scattering mode for both spherical and spheroidal pushers. Our findings highlight a transition in swimming modes influenced by the geometry and dipolarity of the microswimmer.