Aerodynamic characteristics of HAWT rotor in crosswind based on free vortex method

In order to study the aerodynamic characteristics of HAWT rotor under yawed conditions with shear wind, an unsteady numerical simulation method is developed. It consists of a nonlinear lifting line method and a time-accurate free vortex method. To improve the convergence of the nonlinear lifting line method, an iterative algorithm, based on Newton-Raphson method, is used to solve the circulation equations. In order to improve the accuracy and the efficiency of the algorithm for rotor wake simulation, an improved wake vortex model is developed, which includes a viscous vortex core model, a vortex sheet model and a tip vortex filaments model. The NREL Phase VI and Tjæreborg wind turbines are taken as the testing examples. The aerodynamic loads of both the rotor and the blades are computed under different yawed conditions with uniform wind or the shear wind. The results are compared to the experimental data. The key factors and the rules of the aerodynamic characteristics of the rotor and the blades are analyzed. The results show that the method developed in this paper can simulate the aerodynamic characteristics of HAWT effectively under the yawed conditions with shear wind. The fluctuations of shaft torque of blades are increased; the fluctuations of flap moment of blades are decreased at the plus yaw angles and increased at the minus yaw angles.