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 (alpha), squirmer-type factor (beta), blockage ratio (B), and orientation angle (theta). Notably, despite the low Reynolds numbers, a change in the orientation angle theta 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 (beta< 0), the neutral squirmer (beta= 0), and the puller type (beta> 0). These variations were closely tied to the pressure and velocity distributions on the surfaces of the respective squirmers. Furthermore, an increase in alpha 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.