A design methodology for a flexible wind turbine blade with an actively variable twist distribution to increase region 2 efficiency

This paper presents a methodology for designing key features of a flexible wind turbine blade with an actively variable twist distribution. Simulation results suggest this capability can increase the aerodynamic efficiency during Region 2 operation. The concept for the flexible blade consists of a rigid spar with flexible modular segments that form the surrounding shells. The segments are additively manufactured. The associated compliances of the each individual segment and actuator placement determine the Twist Angle Distribution (TAD). It is assumed that the degree of flexibility for each segment will be established through the design and additive manufacturing (AM) processes. Moreover, the variations in compliance make it possible for the blade to conform to the desired set of TAD geometries. The design process first determines the TAD that maximizes the aerodynamic efficiency for discrete points of wind speed in Region 2. The results are obtained using the National Renewable Energy Laboratory (NREL) Aerodyn software and a genetic algorithm. The TAD geometry is then passed to a mechanical design algorithm that locates a series of actuators and defines the stiffness ratio between the blade segments. The process employs a computer cluster to create the TAD for a set of design scenarios. The design selections are found through an objective function. It minimizes the amount of deviation between the actual TAD and that found in the aerodynamic analysis. The free-shape TAD is determined in the final step. The geometry is chosen to minimize the amount of deflection needed to shape the TAD, which changes with Region 2 wind speed. A case study suggests that a blade with only five actuators can achieve the full range of TAD geometry. Moreover, the design solution can increase the efficiency at cut-in and rated speeds up to 3.8% and 3.3%, respectively.