By Dr. Nawal Quennouz
(PMMH ESPCI Paris)
Friday 8th of June 2012 – 10:15 – Room CM011
The interaction of a deformable body with a viscous flow is found in a wide range of situations, ranking from biology to polymer science.
Numerous studies both experimental and theoretical have been devoted to this fi eld, but a large number of questions remains to be answered. The experimental study of simple model systems, such as homogeneous elastic fi bers, evolving in a controlled flow geometry, could help understanding the complex interactions that govern the dynamics.
Here we address the fundamental question of the modi cation of the transport of an object induced by its deformation in a viscous flow as studied by Young  et al.
In this context, we experimentally study the deformation and transport of an isolated elastic fi ber in a viscous cellular flow at low Reynolds number , namely a lattice of counter-rotative vortices. We show that the fi ber can buckle when approaching a stagnation point. By tuning either the flow or the fiber properties, we measure the onset of this buckling instability. The buckling threshold is determined by the relative intensity of viscous and elastic forces, the elasto-viscous number Sp. We compare our experimental results with the numerical simulations by Young  et al and we discuss the origins of the di erences between them.
 Yuan-Nan Young and Mike Shelley. Stretch-Coil Transition and Transport of Fibers in Cellular Flows, Physical Review Letters 99, 058303, 2007.
 Elie Wandersman, Nawal Quennouz, Marc Fermigier, Anke Lindner and Olivia du Roure. Buckled in translation, Soft Matter 6, 57155719, 2010.