(110c) Near-Wall Motion of a Squirmer in Viscoelastic Fluids

Microbial biofilms ubiquitously occur on natural and man-made surfaces and are closely related to various health and environmental issues. During the biofilm formation, the hydrodynamic interaction between microorganisms, surfaces and biofilm itself, which shows viscoelastic properties, are important. Despite this, the hydrodynamic interaction of swimming microorganisms and solid surfaces in viscoelastic fluids is poorly understood. We perform a three-dimensional direct numerical simulation of a microorganism swimming in viscoelastic fluids near a wall. The background viscoelastic fluid is modeled using a Giesekus constitutive equation and the microorganism is modeled using a squirmer model, which is composed of a spherical cell body with a tangential surface motion. We found that the viscoelasticity of the fluid affects the near-wall motion of a squirmer depending on the swimming mode. For a neutral squirmer, the wall-contact time increases with viscoelasticity and reaches a maximum at Wi~1 due to a negative polymeric torque acting on the squirmer and impeding its rotation away from the wall. The neutral squirmer eventually escapes from the wall. On the other hand, the pusher is found to be trapped near the wall in viscoelastic fluids due to the highly stretched polymers behind its body. The near-wall motion of a puller swimmer is less affected in viscoelastic fluids.