  We investigate a typical aerofoil section under dynamic stall conditions, the
structural model is linear and the aerodynamic loading is represented by the
Leishman-Beddoes semi-empirical dynamic stall model. The loads given by this
model are non-linear and non-smooth, therefore we have integrated the equation
of motion using a Runge-Kutta-Fehlberg algorithm equipped with event detection.
The main focus of the paper is on the interaction between the Hopf bifurcation
typical of aero-elastic systems, which causes flutter oscillations, and the
discontinuous definition of the stall model. The paper shows how the non-smooth
definition of the dynamic stall model can generate a non-smooth Hopf
bifurcation. The mechanisms for the appearance of limit cycle attractors are
described by using standard tools of the theory of dynamical systems such as
phase plots and bifurcation diagrams.
