(385c) Swimming with Swirl in a Viscoelastic Fluid

Many of the biological fluids in which microorganisms swim have a complex rheological behavior since they contain large biomolecules that create a rich underlying microstructure. Specifically, these fluids are often viscoelastic, meaning they exhibit both a fluid- and solid-like response to deformation. Heretofore, there has been a great deal of work demonstrating that microswimmers will move either slower or faster in an elastic fluid depending on the particular swimming gait, fluid rheology, and material properties of the swimming body. In particular, it has been shown that the bacteria E. coli swims faster in a viscoelastic fluid than it does in a Newtonian fluid (Patteson et al., 2015). We have recently performed 3D simulations using the well-known squirmer model demonstrating that such a speed enhancement will occur if the swimming microorganism induces a significant amount of swirling flow around its body (created for example by a rotating flagellum and counter-rotating cell body as are characteristic of E. coli). In this talk, we will examine the mechanism of this speed enhancement via an in-depth analysis of the extra polymer stress in the surrounding flow field and a decomposition of the hydrodynamic tractions exerted on the swimmer. We will conclude the talk by exploring how the swimming kinematics are affected when we expand our computational model to consider a run-and-tumble trajectory as well as a periodic precession of the swimmer's orientation (i.e. a "wobbling" motion).