Flow Field Around the Flapping Flag

The flapping flag is a canonical fluid-structure interaction problem that describes a cantilever plate with flow along its elastic axis. When the flapping flag loses stability it enters a large amplitude Limit Cycle Oscillation (LCO). While theoretical models can accurately predict the flutter velocity and frequency, there are still discrepancies between the experimental observations and the theoretical predictions of the post-critical LCO response. This note provides recent flow field visualizations in a single longitudinal plane for a cantilevered aluminum plate in axial flow during its LCO. Particle Image Velocimetry (PIV) techniques are used to show that the flow over the midspan of the plate is attached even during the violent LCO motion. This observation suggests that potential flow aerodynamic models may be able to capture the essential features in the flow field.