Projects per year
Abstract
Shearthinning is an important rheological property of many biological fluids, such as mucus, whereby the apparent viscosity of the fluid decreases with shear. Certain microscopic swimmers have been shown to progress more rapidly through shearthinning fluids, but is this behavior generic to all microscopic swimmers, and what are the physics through which shearthinning rheology affects a swimmer's propulsion? We examine swimmers employing prescribed stroke kinematics in twodimensional, inertialess Carreau fluid: shearthinning “generalized Stokes” flow. Swimmers are modeled, using the method of femlets, by a set of immersed, regularized forces. The equations governing the fluid dynamics are then discretized over a bodyfitted mesh and solved with the finite element method. We analyze the locomotion of three distinct classes of microswimmer: (1) conceptual swimmers comprising sliding spheres employing both one and twodimensional strokes, (2) slipvelocity envelope models of ciliates commonly referred to as “squirmers,” and (3) monoflagellate pushers, such as sperm. We find that morphologically identical swimmers with different strokes may swim either faster or slower in shearthinning fluids than in Newtonian fluids. We explain this kinematic sensitivity by considering differences in the viscosity of the fluid surrounding propulsive and payload elements of the swimmer, and using this insight suggest two reciprocal sliding sphere swimmers which violate Purcell's Scallop theorem in shearthinning fluids. We also show that an increased flow decay rate arising from shearthinning rheology is associated with a reduction in the swimming speed of slipvelocity squirmers. For spermlike swimmers, a gradient of thick to thin fluid along the flagellum alters the force it exerts upon the fluid, flattening trajectories and increasing instantaneous swimming speed.
Original language  English 

Article number  081903 
Journal  Physics of Fluids 
Volume  25 
Issue number  8 
DOIs  
Publication status  Published  Aug 2013 
Bibliographical note
Author Thomas Johnson publishes under MontenegroJohnsonFingerprint
Dive into the research topics of 'Physics of rheologically enhanced propulsion : different strokes in generalized Stokes'. Together they form a unique fingerprint.Projects
 1 Finished

Modelling the Fluid Mechanics of Propulsion through a Complex Microenvironment
Engineering & Physical Science Research Council
7/01/13 → 6/03/14
Project: Research Councils