Self-propulsion of a sticky sphere partially covered with a surface slip velocity

Abstract

Microorganisms follow various strategies to swim in a viscous medium. In an attempt to understand the swimming of ciliated microorganisms, we study low Reynolds number locomotion of a rigid slip-stick swimmer where the propulsive slip velocity is concentrated around an annular patch, which imitates the distinctive surface activity of the microorganisms. In addition, we assume the Navier slip condition at the rigid-fluid interface, which contributes to the hydrodynamic slip or stickiness across the surface. We solve for the locomotion speed and the corresponding flow fields of the swimmer in an axisymmetric unbounded medium. Our analysis reveals insights into how the choice of active slip influences the swimming velocity and the other relevant swimming characteristics. Interestingly, we find that for an optimal active slip in the annular range [π/4, 3π/4], the locomotion speed of the partially covered swimmer is enhanced by a factor of 2 compared to the standard fully covered squirmer. In addition, the corresponding swimming efficiency is enhanced by ∼2.4 times. We independently treat the influence of stickiness of the swimmer on the swimming characteristics. We find that the stickiness reduces the hydrodynamic resistance for the partially covered swimmer and further enhances the swimming speed and efficiency. These findings will be helpful to design efficient artificial swimmers in terms of higher mobility and lower power dissipation.