Vorticity alignment of rigid fibers in oscillatory flow

Rigid fibers suspended at high concentration in a viscous, Newtonian fluid can be aligned perpendicular to the flow-gradient plane by applying an oscillatory shear flow. Direct comparisons with published experiments of Franceschini and coworkers [Phys. Rev. Letters 107, 250603 (2011)] demonstrate that a simple model, which considers only excluded volume and self-mobilities, can accurately predict the orientation distributions. However simulations reveal that this surprising alignment occurs only if the ratio of the gap width to fiber length is small (i.e. a highly confined suspension). Stresses calculated from the numerical simulations are also reported and compared to the experimentally measured rheology.