A nonlinear model for wind turbine blade flutter*

Larger wind turbine blades are more susceptible to flow-induced instabilities such as coupled-mode flutter. Flutter research in wind turbine blades has been primarily focused on predicting the critical flutter point and less so on post-critical flutter behavior.  However, the goal of establishing control mechanisms for wind turbine blade flutter and the possibility of subcritical instabilities have made it essential to derive nonlinear models for these instabilities. We present a nonlinear model for wind turbine blade instability in which the structure is represented by a set of coupled nonlinear partial differential equations, which retain up to third order nonlinearities, and the flow is represented using an ONERA dynamic stall model. The nonlinear model is obtained by coupling these equations, and is solved using the Galerkin technique. The results indicate post-critical limit cycle oscillation, whose amplitude increases with increasing wind speed.