Nonlinear aeroelastic characterization of wind turbine blades

A nonlinear aeroelastic characterization of wind turbine blades is performed. A two di- mensional aerodynamic model based on the quasi-steady approximation is coupled with a plunging and pitching airfoil section of the blade. The normal form of the Hopf bifurcation is derived and used to characterize the blade's response. Based on a linear analysis, it is determined that for higher values of the blade radius and/or higher values of the operating rotational speeds, wind turbine blades are more susceptible to utter at a freestream velocity close to the cut-out speed. Nonlinear analysis is performed based on the normal form of the Hopf bifurcation. The results show that depending on the nonlinear structural parameters and initial conditions, wind turbine blades could have subcritical instability which means that high limit-cycle oscillation amplitudes can take place at freestream velocities below the linear utter speed.