Nonlinear dynamics of silk and Mylar flags flapping in axial flow

In this study, experiments were conducted on the flapping dynamics of flags immersed in fairly noisy axial flow. The experimental set-up was first validated by comparing the critical conditions for flapping onset with relevant results from other experimental investigations, numerical simulations and theoretical models found in the literature. Short and long flags, as well as flags with aspect ratio equal to unity, were considered. Nonlinear dynamic analyses including power spectra, phase-space portraits, Poincaré sections and circle maps obtained from the flag transverse displacement time-series indicate that the observed non-periodic flapping mainly arises through a quasi-periodic scenario. This paper also reports for the first time a "switching" oscillation phenomenon, which is closely related to hysteresis and bistability phenomena.