Experimental study on the post-flutter morphological chracteristics and energy dissipation of a 15 MW wind turbine blade

Most existing flutter analyses of wind turbine blades focus on predicting critical flutter states. While the post-flutter morphological evolution and the associated energy dissipation, well-known for the prominent non-linear effect, are usually ignored. To characterize this non-linear phenomenon, a three-dimensional aeroelastic model of ultra-long flexible blades is proposed using the variational progressive beam section method. And synchronous measurements of vibration and force are carried out in a wind tunnel using high-speed cameras and a high-frequency six-component balance. The flutter sensitivity of wind turbine blades to the wind direction and speed is firstly analyzed. Later, the post-flutter morphological characteristics and the energy dissipation of wind turbine blades subjected to wind-induced vibration are systematically studied. Results indicate that the proposed aeroelastic model and the experimental method can effectively capture the post-flutter dynamic process. The pitch angles of wind turbine blades prone to the wind-induced vibration fall in two ranges, namely 93° ~ 96° and 284° ~ 286°, in which high-frequency locking vibrations can occur beyond the critical wind speed. At the same time, the energy accumulation becomes particularly significant at higher wind speeds, indicating that the wind-induced vibrations are non-stationary. The negative post-flutter aerodynamic damping is the main reason for the divergence of structural systems.