A CFD analysis of NREL's 5MW wind turbine in full and model scales

In the present paper, a commercial CFD code based on RANS equations is used to assess the aerodynamic behavior of the rotor of NREL's 5MW turbine. The main objective is to evaluate the changes that happen in the wind flow when the scale of the problem is reduced based on Froude-scale law, a procedure that is used for tests of floating wind turbines in wave basins, such as the ones performed as part of the OC4 program. Therefore, the CFD simulations are performed both for real and model scales, considering a range of tip-speed ratios, and the scale effects involved in the aerodynamics of the blades are presented and discussed. The results are compared to experimental and numerical data of the same rotor available in the literature, especially in terms of thrust and power coefficients. As main conclusions, it is found that the present CFD predictions for the rotor in full scale are generally in accordance with the previous numerical data. More importantly, for the model-scale rotor, it is shown that a very good agreement with the experimental data could be obtained, even for the negative power coefficients that happen for certain tip-speed ratios, something that the previous numerical works have reported to be more difficult to reproduce.