Rotational modes of motion for an aerodynamic pendulum with a vertical rotation axis

An aerodynamic pendulum placed in a steady horizontal air flow is studied in connection with modeling a wind-receiving element of a vertical-axis wind turbine (VAWT). When modeling the medium effects on the pendulum, the following two approaches are combined: the quasi-static one based on stationary wind tunnel experiments and the unsteady one based on the added mass effects. The existence of stable and unstable rotational modes is analyzed analytically (via the Poincaré-Pontryagin method) and numerically. The dependence on the parameters responsible for the viscous friction at the rotation axis and for the added mass effects is taken into account.