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

Abstract

Abstract 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.