Rotational dynamics of a soft filament: Wrapping transition and propulsive forces

Naïs Coq (1) , Olivia Du Roure (1) , Joël Marthelot (1) , Denis Bartolo (1) , Marc Fermigier (1)

1 PMMH - Physique et mécanique des milieux hétérogenes (UMR 7636)

We experimentally analyze the shape of a long elastic filament rotating in a viscous liquid. We identify a continuous but sharp transition from a straight to an helical shape, resulting from the competition between viscous stresses and elastic forces. This induced helicity generates a propulsive force along the axis of rotation. In addition, we show that the shape transition is associated with an unstable branch in the force-torque relation, confirming the numerical predictions of Manghi et al. [Phys. Rev. Lett. 96, 068101 (2006)]. A linearized model of the fluid-structure interaction is proposed to account for all the features of the nonlinear filament dynamics.

Domaines: Matière Molle [cond-mat.soft]; Mécanique des fluides [physics.class-ph]

Naïs Coq, Olivia Du Roure, Joël Marthelot, Denis Bartolo, Marc Fermigier. Rotational dynamics of a soft filament: Wrapping transition and propulsive forces. Physics of Fluids, 2008, 20, pp.051703. ⟨10.1063/1.2909603⟩. ⟨hal-00343588⟩