Heavy flags undergo spontaneous oscillations in flowing water

Michael Shelley (1) , Nicolas Vandenberghe (1, 2) , Jun Zhang (3, 1)

1 AML - COURANT INSTITUTE - Applied Math Laboratory Courant Institute of Mathematical Sciences
2 IRPHE - Institut de Recherche sur les Phénomènes Hors Equilibre
3 Department of Physics [New York]

By immersing a compliant yet self-supporting sheet into flowing water, we study a heavy, streamlined, and elastic body interacting with a fluid. We find that above a critical flow velocity a sheet aligned with the flow begins to flap with a Strouhal frequency consistent with animal locomotion. This transition is subcritical. Our results agree qualitatively with a simple fluid dynamical model that predicts linear instability at a critical flow speed. Both experiment and theory emphasize the importance of body inertia in overcoming the stabilizing effects of finite rigidity and fluid drag.

Mots clés: drapeau; couplage fluides-structures

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]; Mécanique des structures [physics.class-ph]; Mécanique des structures [physics.class-ph]; Vibrations [physics.class-ph]; Vibrations [physics.class-ph]

Michael Shelley, Nicolas Vandenberghe, Jun Zhang. Heavy flags undergo spontaneous oscillations in flowing water. Physical Review Letters, 2005, 94, pp.094302. ⟨10.1103/PhysRevLett.94.094302⟩. ⟨hal-00014594⟩