Shaping it up: how aspect ratio affects the dynamics of flapping flags

Flexible objects like flags remain steady in a low-velocity flow but undergo high-magnitude flapping beyond a critical velocity. Prior studies on the fluid-structure interaction of flags have mainly focused on the instability mechanisms. The influence of the flag's morphology on its deflection and interaction with the unsteady wake flow has received less attention. We specifically focus on the effect of aspect ratio on the flapping dynamics of rectangular flags. We install paper flags of different shapes in an open-section wind tunnel. The experimental set-up is fully automated, which enables to explore a large range of geometries at varying wind speeds. A load cell and an event-based camera provide time-resolved force and deformation measurements. Our results suggest that the aspect ratio does not affect the onset of flapping but affects the dynamic response in the flapping regime. Variations of Strouhal number and other metrics will reveal the role of three-dimensional effects in the dynamics of flapping flags.