Related Experiment Video
Updated: Aug 12, 2026

Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing
Published on: February 13, 2018
Heavy flags undergo spontaneous oscillations in flowing water
Michael Shelley1, Nicolas Vandenberghe, Jun Zhang
1Applied Mathematics Laboratory, Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, New York 10012, USA.
Abstract:
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.
More Related Videos
Related Concept Videos
Damped Oscillations
Although friction and other non-conservative...
Types of Damping
Forced Oscillations
Standing Waves
Gradually Varying Flow
Rapidly Varying Flow

