Study on the sedimentation and interaction of two squirmers in a vertical channel

We simulated the sedimentation of two self-propelled particles in a two-dimensional (2D) vertical channel using the lattice Boltzmann method. A 2D squirmer model was employed to simulate the microswimmers, and five typical locomotive modes were obtained for a single squirmer, namely, central steady sedimentation, near-wall steady motion, wall-attracted oscillation, large-amplitude oscillation, and small-amplitude oscillation. The locomotive modes of two squirmers are obtained by combinations of different locomotive modes of a single squirmer. It was found that the motion of two squirmers was much more complex than that of a single squirmer, and this complex locomotive mode could be explained by the pressure distribution of the two squirmers. Moreover, we performed a comprehensive analysis of the obtained locomotive modes and determined that the angle at which the two squirmers separated from each other and swimming speed were crucial, which may be the reason for the different locomotive modes of the squirmers that switch from each other.