Signatures of cross-streamline migration of elastic fibers in microscale flows

The complex dynamics of elastic fibers in viscous fluids are vital in many biological and industrial systems. Understanding these dynamics can help elucidate the behavior in confined suspension systems and tune flow properties in applications such as printing and clogging. In this work, we use slender-body theory in numerical simulations to study microscale dynamics that contribute to cross-streamline migration. In unidirectional flows, a buckled fiber can make a tank-treading motion, resulting in the fiber drifting away from its original position. The magnitude of the net drift between an upward and downward motion differs if the shear rate spatially varies. We then perform simulations of a Brownian fiber to show the fiber’s ability to move from regions of low to high shear. In Poiseuille flow, this results in selective migration towards walls, where the steady-state position is determined by the hydrodynamic drift towards the walls and the steric repulsion from them. We develop scaling laws for the extent of this depletion layer. Collectively, these results highlight the importance of the fiber’s microscale dynamics towards its macroscopic behavior, providing the groundwork to connect elastohydrodynamics and fiber suspensions in confined microfluidic geometries.