Heavy flags undergo spontaneous oscillations in flowing water

Michael Shelley, Nicolas Vandenberghe, Jun Zhang

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Article number094302
JournalPhysical Review Letters
Issue number9
StatePublished - Mar 11 2005

ASJC Scopus subject areas

  • General Physics and Astronomy


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