Abstract: When in a flow, an object deviates it and from this deviation are generated vortices and flow reaction forces, such as drag and lift. If the object is free to move, its movement can couple with the surrounding flow, falling into the domain of fluid-structure interactions.
In this presentation, the coupling between a pendular system and an air flow is studied both experimentally and theoretically. Placed in a wind tunnel, a disk pendulum presents bistability for a range of flow velocity. Spontaneous transitions between the two stable states are observed and studied statistically. A model, inspired from the transition to turbulence, suggests certain mechanisms in the wake that trigger such transitions, in particular rare aerodynamic events. The visualization of first the steady wake and then the dynamic wake during a transition provides insight on the aerodynamic phenomena at work.