Gaojin Li

Collective Motion of Microorganisms in a Viscoelastic Fluid

We study the collective motion of a suspension of rodlike microswimmers in a two-dimensional film of viscoelastic fluids. We find that the fluid elasticity has a small effect on a suspension of pullers, while it significantly affects the pushers. The attraction and orientational ordering of the pushers are enhanced in viscoelastic fluids. The induced polymer stresses break down the large-scale flow structures and suppress velocity fluctuations. In addition, the energy spectra and induced mixing in the suspension of pushers are greatly modified by fluid elasticity.

Near wall motion of undulatory swimmers in non-Newtonian fluids

We investigate the near-wall motion of an undulatory swimmer in both Newtonian and non-Newtonian fluids using a two-dimensional direct numerical simulation. Our results show that the undulatory swimmer has three types of swimming mode depending on its undulation amplitude. The swimmer can be strongly attracted to the wall and swim in close proximity of the wall, be weakly attracted to the wall with a relatively large distance away from the wall, or escape from the wall. The scattering angle of the swimmer and its hydrodynamic interaction with the wall are important in describing the near-wall swimming motion. The shear-thinning viscosity is found to increase the swimming speed and to slightly enhance the wall attraction by reducing the swimmer’s scattering angle. The fluid elasticity, however, leads to strong attraction of swimmer’s head towards the wall, reducing the swimming speed. The combined shear-thinning effect and fluid elasticity results in an enhanced swimming speed along the wall.