Bifurcation and synchronization analysis in a stall-flutter aeroelastic system under varying preset angles and frequency ratios

This study experimentally investigates the bifurcation characteristics and synchronization mechanisms in an aeroelastic system exhibiting nonlinear stall flutter behaviour, with particular emphasis on the influence of varying preset angles of incidence and frequency ratios. To that end, wind tunnel experiments are performed on a NACA 0012 aerofoil, which incorporates structural nonlinearities in stiffness as well as aerodynamic nonlinearities resulting from the dynamic stall effect. Bifurcation routes are identified for preset angles of incidence ranging from [Formula: see text] to [Formula: see text] and frequency ratios ([Formula: see text]) between 0.56 and 0.75 by systematically varying the flow speed. The aeroelastic responses in the pitch and plunge are analyzed to determine the onset of Hopf bifurcation and synchronization behaviors within the system. A series of altered bifurcation scenarios exhibiting diverse dynamical behaviours is observed, demonstrating a change in the system's subcriticality, characterized by a decrease in both the subcritical regime and flutter velocity. Synchronization analysis shows strong coupling between the pitch and plunge responses for preset angles ranging from [Formula: see text] to [Formula: see text]. However, at [Formula: see text], an asynchronous regime is identified, characterized by the occurrence of low amplitude limit cycle oscillations (LCOs). Additionally, a frequency-specific analysis in the asynchronous regime shows that high-frequency pitch and plunge components remain synchronized, while low-frequency components exhibit intermittent phase synchronization. The novelty of this work lies in presenting the first experimental study that systematically investigates bifurcation and synchronization behaviour across a wide range of preset angles and frequency ratios, providing essential insights for the design of advanced aeroelastic structures.