Optical measurements of multi-megawatt wind turbine dynamic response

A novel opto-mechanical platform to measure the dynamic response of a multi-megawatt wind turbine is developed and applied. This opto-mechanical platform measures the blade shape, blade deflections and characteristics of blade vibrations by tracking blade during operation without need for any modification or attachment to the turbine. Simultaneous measurements of the wind speed, wind direction, and turbulence intensity are made with a LiDAR scanning system. It is shown that there is an azimuthal variation of wind speed (that is major loads), turbulence (that is minor loads) during a rotor revolution which consequently leads to azimuthal variations of the blade's vibration and fatigue loads during a rotor revolution. Measurements show a 4% higher level of blade vibrations in the top-most position compared to the bottom-most position. A maximum deflection of 6.5% of the blade length at the top-most position is measured. Measurements and BEM analysis show that loading on the blade at the bottom-most position contributes 30% more to the blade's fatigue life (the number of cycles to failure at measured loading conditions) compared to the blade loading at the top-most position. These findings show that the opto-mechanical platform can be used to develop more accurate predictions of fatigue lifetime.