A variable twist blade for horizontal axis wind turbines: Modeling and analysis

A method for analyzing the performance of a wind turbine blade design with an adaptive variable twist is presented. The possibility of implementing morphing features is becoming increasingly possible with innovative materials and manufacturing techniques. This motivates a blade concept consisting of multiple shell sections mounted on a rigid spar and covered by non-structural skin. The design allows the blade shells to adapt the twist angle distribution (TAD). The study is conducted using data acquired from the National Renewable Energy Laboratory (NREL) 20 kW wind turbine. A design problem is formulated to find the TAD that maximizes the aerodynamic efficiency for a discrete set of points that represent the Region 2 wind speed. The TAD is found for each point using a heuristic search algorithm. This algorithm searches through performance data that is acquired using the AeroDyn open source simulation software. Results from the model are validated with computational fluid dynamics (CFD) simulations using the Reynolds-averaged Navier-Stokes equations with the k-omega shear stress transport turbulence model. Through this first part of the analysis, it becomes possible to understand the required amount of blade deformation by the TAD function. Given this understanding, a stress analysis can be performed on the blade structure. The scenario considers the combined effect of twisting with aerodynamic loading. The blade load is determined by combining CFD with finite element analysis to facilitate the one-way fluid-structural interaction. The outcome of this work demonstrates how the proposed method can be used to determine the gain in efficiency, required range of motion, and structural performance of the blade shells for a given wind turbine blade design.