Deformation and transport of an elastic fiber in a cellular flow

Flexible fibers can undergo a buckling instability when they are in interaction with a viscous flow. It has been predicted numerically that the deformation of an elastic fiber can affect both the macroscopic rheology and the transport of the individual fiber through a cellular flow [1]. However, direct experimental observations of the coupling between fiber conformation and flow behavior are still missing. We study experimentally the deformation and the transport of an individual elastic fiber (Length $L \sim 1$ cm, radius $r \sim 100 \mu$m, Young's modulus $Y \sim 0.1$ MPa) in a cellular flow formed by a lattice of hyperbolic stagnation points. In the vicinity of a stagnation point, the fiber buckles if the viscous forces acting on the fiber overcome the elastic forces. We focus on: \begin{itemize} \item the onset of the buckling instability of the fiber, varying the elastic properties of the fiber, the shear rate and the ratio fiber length to the cell size. \item The dynamical properties of the fiber, and more precisely, the modification of the transport of the fiber in the lattice due to its deformation in the flow. \end{itemize} [1] Young et. al. \textit{Phys. Rev. Lett.} \textbf{99} 058303 (2007)