The hydrodynamic characteristics of a squirmer swimming in a lid-driven cavity

Abstract

This article employs the Lattice Boltzmann method (LBM) to investigate the hydrodynamic characteristics of a squirmer, modeled after a classic microbial, swimming in a lid-driven cavity. The study analyzes the effects of self-propulsion strength (β), fluid inertia caused by the swimming Reynolds number (Re_s), shear Reynolds number (Re) of the flow field, and the particle-to-cavity size ratio k on the swimming behavior of the squirmer. Three typical swimming modes are defined: closed-loop swimming, periodic swimming, and directional trapping. The results show that β and Re_s jointly affect the transitions between these modes, with stronger self-propulsion and fluid inertia favoring directional trapping. During directional trapping, although the squirmer remains relatively stationary, it interacts with the surrounding fluid, potentially causing the development of multiple secondary vortices. Increasing Re induces a transition from the mode of closed-loop swimming to directional trapping, particularly when Re ≥ 500. The particle-to-cavity size ratio also influences the movement of the squirmer, particularly in the case of the Puller (one kind of squirmer). Pusher (the other kind of squirmer) consistently maintains the closed-loop swimming mode, while Puller experiences multiple swimming mode transitions. These findings contribute to a deeper understanding of the dynamic interactions of microswimmers in complex environments, providing valuable insights for designing microrobots for biomedical applications.