SMART AERODYNAMIC CONTROL DEVICES DESIGN AND VIBRATION REDUCTION ANALYSIS FOR WIND TURBINE BLADES

This study aims to design several types of aerodynamic control devices using smart material actuators to reduce the vibration fatigue load of wind turbine blades. The concepts of piezo stack actuator based smart external and internal flaps were detailed, including the basic flap layout, the operating range, the settings, etc. The concept of ionic polymer metal composite based microflap was also detailed. In order to compensate the aerodynamic force, centrifugal force and gravitational force acting on the flap under the wind turbine’s normal operational conditions, the required energy output from the actuators was calculated. To meet the energy requirements, the configuration of actuator array was determined. Amplification systems were designed to enhance the displacement output at the expense of the force output. In addition, a universal flap control scheme was developed using the multiblade coordinate transformation, the gain scheduling technique and the proportional-integral-derivative controller. A series of aeroelastic-aerodynamic time marching simulations were performed on the NREL 5MW wind turbine with the designed flap systems and control scheme in order to obtain the time responses. The time domain data was analyzed from a fatigue perspective. The result shows there are significant reductions in the vibration fluctuation and the damage equivalent loads, with respect to the blade out-of-plane deflection and the blade root flapwise bending moment. To further investigate the effects of flap on the natural frequency of the wind turbine, the operational modal analysis was used to extract the modal parameters from the operating wind turbine. However, the operational modal analysis cannot be directly applied to the time series, which is because the assumptions are violated for the operating wind turbine and the harmonic frequencies raised from the rotational motion mask quantities of natural frequencies of the structural modes. In order to overcome this problem, a cepstral harmonic removal method was developed based on a mathematic development of a modified notch lifter. After the linearization direct eigenvalue analysis and the operational modal analysis were applied, both results show that the flap system slightly reduces the resonance frequencies