In an experiment on thin flat strips falling through a fluid in a vertical cell, two fundamental motions are observed: side-to-side oscillation (flutter) and end-over-end rotation (tumble). At high Reynolds number, the dimensionless similarity variable describing the dynamics is the Froude number $\mathrm{Fr}$, being the ratio of characteristic times for downward motion and pendular oscillations. The transition from flutter to tumble occurs at ${\mathrm{Fr}}_c=0.67\mathrm{}\pm 0.05$. We propose a phenomenological model including inertial drag and lift which reproduces this motion, and directly yields the Froude similarity.

• Received 28 October 1997

DOI:https://doi.org/10.1103/PhysRevLett.81.345