Simulation of flow past a squirmer confined in a channel at low Reynolds numbers

The two-dimensional lattice Boltzmann method was employed to numerically investigate the flow around a circular squirmer in a channel at low Reynolds numbers. The study thoroughly examined the impact of various factors on flow structures and drag coefficients ( C d ) of the squirmer, such as the Reynolds number ( Re ), self-propelled strength ( α ), squirmer-type factor ( β ), blockage ratio ( B ), and orientation angle ( θ ). Notably, despite the low Reynolds numbers, a change in the orientation angle θ resulted in a lift in the squirmer, consequently affecting its lift coefficient ( C l ). The simulation findings underscored that a pair of up-down backflow regions are generated on the squirmer’s surface. Interestingly, the locations of these backflow regions varied significantly between the pusher type ( β < 0), the neutral squirmer ( β = 0), and the puller type ( β > 0). These variations were closely tied to the pressure and velocity distributions on the surfaces of the respective squirmers. Furthermore, an increase in α might induce the formation of a new pair of backflow regions near the channel walls and subsequently elevate the C d . On the other hand, alterations in Re did not affect the flow structures but created a negative correlation with C d . Overall, the study unveiled unique dynamic characteristics, offering a contrast to the extensively investigated case of flow past a cylinder.