Field Testing and Simulating Servo-Aero-Gravoelastically Scaled Rotors for Extreme-Scale Wind Turbines

Wind energy continues to grow as a valuable source of renewable energy due to the reduction in the levelized cost of energy over time. To achieve this growth, wind turbine sizes are growing beyond those predicted by conventional rotor designs. The increased turbine size allows for higher tower heights, accessing higher atmospheric wind speeds, and larger rotor diameters, allowing for more power capture. Such turbines are considered extreme-scale turbines (greater than 10 MW rated power) and consist of blades in excess of 100 meters in length. To reduce the gravitational loadings on blades of such sizes, the blades are designed to be lightweight which leads to highly flexible rotors as compared to conventional wind turbine blade designs. While computational methods have been developed and verified for conventional rotors, it is unknown if they are capable of capturing the dynamics of the highly-flexible, extreme-scale turbines. Experimental testing of the rotors can alleviate any uncertainties with simulations in fully understanding the interaction of gravitational, aerodynamic and elastic loads. While full-scale rotor testing is ideal to capture these dynamics, it can be prohibitively expensive in terms of both time and cost. Therefore, a sub-scaling method which captures the full-scale dynamics can prove beneficial to the development of novel extreme-scale designs. In this study, a method for sub-scaling these ‘extreme-scale’ rotors is developed, applied, and verified through three different sub-scale turbine model designs. The scaling methods are based on a gravo-aeroelastic scaling (GAS) method which ensures the gravitational, aerodynamic, and elastic interactions of the full-scale blades are captured at a fraction of the cost in terms of time to build and materials needed. The following study begins with outlining the requirements of a computationally ideally-scaled turbine and describing the desired results of a sub-scale model based upon an extreme-scale rotor. This leads to a 1% additively manufactured blade model utilizing a bio-inspired designs in order to maintain the defined scaling requirements and is verified through structural testing. Finally, this study concludes with a 20% scale manufactured model based on the gravo-aeroelastic scaling method for experimental testing at the National Renewable Energy Laboratory’s Flatirons Campus. This model is then verified and compared against computational results for both parked and operational conditions.