Jonas Smucker, UT-Austin

"Dynamical Properties of Fluid-immersed Hair Beds"

Abstract: Fluid immersed hair beds are a common occurrence in organisms. Bronchial cilia, the endothelial glycocalyx layer, and intestinal microvilli (among others) serve critical regulatory functions. To better understand these functions, and the role of passive hairs on fluid dynamics in biological settings, we investigate the transient characteristics of hair beds immersed in a low Reynolds number environment. The steady shear case is first considered, and we derive an analytic solution to the profile of a boundary hair placed in Couette flow. Next, large amplitude oscillatory rheology experiments are conducted with the hair-beds and the response is characterized with the mechanical impedance, a quantity describing the system’s effective viscosity. While the fluid and solid both have linear constitutive properties, we show that interactions between hair-bed deformations and fluid flows induce a nonlinear relationship between the forcing parameters and the system’s impedance, contrasting the rigid limit. The nonlinearity of the system, and the ability of the hairs to respond with many degrees of freedom to shear makes them an interesting candidate to stir fluids. We intend on investigating this application further by studying the performance of hairs as micromixers.