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 yet the object is free to move, its movement can couple with the surrounding flow, falling into the domain of fluid-structure interactions. In this PhD thesis, 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 a bistability for a range of flow velocity, while a rectangular one does not. By varying the aspect ratio of such rectangle and visualizing the wake behind a fixed disk, we propose an origin on whether or not the bistability emerges, linking it to stall phenomenon. The influence of ambient turbulence on this phenomenon is then investigated together with the link between angular fluctuations and flow variations, both upstream and downstream. Going back to the bistability itself, spontaneous transitions between stable states are observed and a model inspired from the transition to turbulence suggest certain mechanisms in the wake triggering such transitions, in particular rare aerodynamical events. Modifying geometrical parameters of the pendulum enables the adjustment of the range of velocity for which the bistability occurs, and with it, we could observe jumps between both transitions at the same flow rate. Finally, when the pendulum is balanced, its movement is only driven by the flow and while a quasi-static modelling is not sufficient to describe the real dynamics of the pendulum, we introduce two ways of accounting for the dynamical retroaction of the flow in the equation of movement, one empirical and the other based on vortex-induced vibration theory.
Gratuit
Disciplines