Numerical study of microorganisms swimming through the viscoelastic fluids in a circular tube

Microorganisms exhibit complex behavioral dynamics in confined tube flows. In this study, we employ the fictitious domain method combined with the squirmer model to investigate the locomotion of microorganisms in a viscoelastic fluid within a circular tube at low Reynolds number. Our results demonstrate that fluid elasticity and tube blocking ratio significantly influence the squirmer swimming speed, power, and efficiency. Specially, the squirmer parameter β, corresponding to a hydrodynamic force dipole, and fluid elasticity critically affect the swimming mode. Neutral swimmers exhibit periodic motions, with fluid elasticity slightly increasing their oscillation periods. Pullers initially migrate radially before stabilizing either along the tube centerline at low β values or near the wall at high β values. Notably, the critical β value first increases and then decreases with increasing fluid elasticity. Pushers, in contrast, display irregular trajectories and ultimately collide with the wall.