Study of blade torsional effect on the aerodynamic performance of wind turbine using a modal superposition method

In this paper, a wind turbine aeroelastic model consisting of a Blade Element Momentum (BEM) model for the aerodynamic part and Euler-Bernoulli Beam (NEBB) model including a torsional degree of freedom (DOF) for the structure part is developed. Through a time-domain aeroelastic analysis of the NREL 5 MW, DTU 10 MW, and IEA 15 MW reference wind turbines, the effect of the torsional DOF is quantified on the aerodynamic performance of the turbines. Results show that the developed model agrees well with Computational Fluid Dynamics (CFD)-Computational Structural Dynamics (CSD) results in the cases of the three reference turbines. For the NREL 5 MW, DTU 10 MW, and IEA 15 MW turbines at rated wind speeds, the differences in blade tip deflections are 6.21 %, 5.31 %, and 7.71 % and the differences in thrust are 12.42 %, 0.90 %, and 1.35 %, respectively. Compared to ElastoDyn in OpenFAST, the model reduces prediction errors from 12.04 % to 6.32 % for NREL 5 MW, and achieves a fivefold error reduction from 17.08 % to 3.26 % for IEA 15 MW relative to CFD benchmarks. Results indicate that the pitch location is important to be considered in blade design to optimize the aerodynamic performance and reduce blade loads. Neglecting torsional DOF will lead to overestimated loads and deformations while underestimating edgewise bending moments at the blade root, which could significantly impact wind turbine designs.