(479b) Fiber Alignment in Confined Shearing Flows

Rigid fibers suspended in a viscous, Newtonian fluid can be aligned perpendicular to the flow-gradient plane by applying an oscillatory shear flow. Here, measurements and simulations of the orientation distribution are reported over a wider range of concentrations, strain amplitudes, and confinements than previously studied. The fibers were non-colloidal and neutrally buoyant, and the strain amplitude and confinement were varied using a custom-built shear cell. The measurements confirm that fibers align in the vorticity direction when oscillated with strain amplitudes of approximately 2 to 3, a volume fraction of 0.15, and gap width to particle length of 1.5 [Franceschini et al., Phys. Rev. Lett. 107, 250603, 2011]. Predictions from simulations [Snook et al., Phys. Fluids 24, 121702, 2012] that the vorticity alignment depends upon the confinement are compared against the experimental measurements. The simulations include only the self-mobilities and a simple contact-force model to enforce the excluded volume, and the results provide evidence that the irreversibilities in the oscillating suspension arise from particle contacts.