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

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

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

We analyze experimentally 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. A linearized model of the fluid-structure interaction is proposed to account for all the features of the non-linear filament dynamics.

Domaines: Dynamique des Fluides [physics.flu-dyn]

Naïs Coq, Olivia Du Roure, Joel Marthelot, Denis Bartolo, Marc Fermigier. Rotational dynamics of a soft filament: wrapping transition and propulsive forces. 2008. ⟨hal-00250302⟩