Fluid Mechanics Seminar: Gwynn J. Elfring

The vast majority of organisms, because of their small size, live in a regime where their inertia is negligible. Familiar strategies for locomotion through fluids, such as imparting momentum onto the surrounding medium, are ineffective at this scale due to the dominance of viscous dissipation. Instead, these organisms must propel themselves by other means in this restrictive environment. Moreover, microorganisms such as bacteria often swim in fluid environments that cannot be classified as Newtonian. Many biological fluids contain polymers or other heterogeneities which may yield complex rheology. For a given set of boundary conditions on a moving organism, flows can be substantially different in complex fluids, while non-Newtonian stresses can alter the gait of the microorganisms themselves. Heterogeneities in the fluid may also be characterized by length scales on the order of the organism itself leading to additional dynamic complexity. In this talk I present a theoretical overview of small-scale locomotion in complex fluids with a focus on recent efforts quantifying the impact of non-Newtonian rheology on swimming microorganisms. Additionally, due to the long range decay of flow fields at this scale, the interaction between multiple swimming organisms can be highly non-local and complex in nature. We will discuss these hydrodynamic interactions, and we will quantify the effects of geometry and elasticity on the system's dynamics.