Nonlinear aeroelastic characterization of wind turbine blades

A nonlinear aeroelastic characterization of wind turbine blades is performed. A two-dimensional aerodynamic model based on the quasi-steady approximation is coupled with a plunging and pitching blade section. The governing nondimensional equations are derived. The normal form of the Hopf bifurcation is derived and used to characterize the behavior of the system. Using linear analysis, it is demonstrated that, as the blade radius and/or operating rotational speed are increased, wind turbine blades become more susceptible to flutter at freestream velocities that are close to the cut-out speed. The nonlinear analysis, based on the normal form of the Hopf bifurcation, shows that, depending on the nonlinear structural parameters and initial conditions, subcritical instability may take place which means that high limit-cycle oscillation amplitudes may take place at freestream velocities that are lower than the linear flutter speed.