Identification of wind inflow characteristics from nacelle lidar measurements in the induction zone of a 9 MW wind turbine

Abstract

For large rotor wind turbines, identifying inflow wind characteristics is crucial for their design and operation. During the design stage, anemometers are commonly used to observe wind shear, turbulence spectra, coherence, and turbulence intensity. However, for large wind turbines, anemometers often take measurements below the hub height, leading to discrepancies between actual wind conditions above the hub height and those assumed during the design stage. This makes it challenging to achieve a closed-loop design and compromises the safe operation of large-scale wind turbines. Nacelle-based wind lidar systems can observe wind conditions above and below the hub height in front of the rotor, providing a wind preview for feed-forward control. However, lidar systems designed for feed-forward control often take measurements within the rotor’s induction zone, where wind speeds are lower in regions closer to the rotor. State-of-the-art wind turbine simulations are primarily based on blade element momentum theory. Both wind turbine controller design and load validation require free-stream incoming wind characteristics as input conditions. Therefore, this paper presents a method for identifying free-stream inflow wind characteristics using a lidar system with a maximum measurement distance of 200 m in front of the rotor. The study is based on a 9 MW turbine with a rotor diameter of 230 m and is of great significance for guiding the wind energy industry in both load verification and feed-forward control improvements using nacelle lidar.