Development and validation of a CFD-based Actuator-Disk/Blade-Element-Theory method for the performance analysis of wind turbines

Nowadays, industries often evaluate the performance of wind turbines adopting simple engineering aerodynamic models, such as the Blade-Element/Momentum Theory. However, more advanced methods are required both to assess the accuracy of these simplified models and to effectively analyze the behavior of wind turbines in real contexts. Critical issues are represented by the proper and effective prediction of the wind turbine wake characteristics, especially in wind farm and complex terrain configurations. This paper develops a CFD-Actuator-Disk/Blade-Element-Theory coupled model and validates it in terms of both global and local flow quantities. The method replaces the real rotor with an actuator disk and simulates the effect of the turbine on the flow field through body forces used as source terms in the momentum equation. The proposed approach is tested and validated with the help of reference wind turbine data namely, the NREL Phase VI and the MEXICO rotor. The comparison shows a very good agreement with the experimental data. In fact, for the NREL Phase VI turbine, both global performance coefficients and radial force distributions are well-predicted, with a power coefficient relative error of 0.51% near design conditions (wind speed equal to 7 m/s). Furthermore, for the MEXICO wind turbine, the wake flow field is compared with azimuthally-averaged three dimensional measurements, showing a good agreement in all analyzed operating conditions.