Wake impact on aerodynamic characteristics of horizontal axis wind turbine under yawed flow conditions

Wind turbines spend most of time in complex and unsteady environment, such as yawed flow, atmospheric wind turbulence, wind shear, and gust. Under yawed flow condition, velocity component parallel to the rotating plane causes a development of skewed wake structure, thus leading to an azimuthal variation in the aerodynamic loads on wind turbine blades. Moreover, the trailing and shed wake vortices unequally expand, and a strong wake interaction between the hub and tip vortices, and the asymmetrical velocity deficit around the rotor area occur. In the present study, the impacts of the skewed wake on the unsteady aerodynamic behavior around rotor blade were numerically investigated and a wake deflection mechanism was discussed in detail. For this purpose, the nonlinear vortex lattice method (NVLM) coupling with a time-accurate vortex particle method (VPM) was used. A numerical simulation on the NREL Phase VI wind turbine model, exposed to a low wind speed with different yaw angles, was carried out and predicted results were compared against measurements. Comparison results showed that the aerodynamic loads can be accurately calculated, even for highly yawed flow conditions and complex wake dynamics can be clearly observed. (C) 2019 Elsevier Ltd. All rights reserved.