Near- and far-field hydrodynamic interaction of two chiral squirmers

Hydrodynamic interaction strongly influences the collective behavior of microswimmers. With this work, we study the behavior of two hydrodynamically interacting self-propelled chiral swimmers in the low Reynolds number regime, considering both the near- and far-field interactions. We use the chiral squirmer model [see Burada et al., Phys. Rev. E 105, 024603 (2022)2470-004510.1103/PhysRevE.105.024603], a spherically shaped body with nonaxisymmetric surface slip velocity, which generalizes the well-known squirmer model. The previous work was restricted only to the case, while the far-field hydrodynamic interaction was influential among the swimmers. It did not approach the scenario while both the swimmers are very close and lubrication effects become dominant. We calculate the lubrication force between the swimmers when they are very close. By varying the slip coefficients and the initial configuration of the swimmers, we investigate their hydrodynamic behavior. In the presence of lubrication force, the swimmers either repel each other or exhibit bounded motion where the distance between the swimmers alters periodically. We identify the possible behaviors exhibited by the chiral squirmers, such as monotonic divergence, divergence, and bounded, as was found in the previous study. However, in the current study, we observe that both the monotonic convergence and the convergence states are converted into divergence states due to the arising lubrication effects. The lubrication force favors the bounded motion in some parameter regimes. This study helps to understand the collective behavior of dense suspension of ciliated microorganisms and artificial swimmers.