基于自由涡方法的风轮偏航气动特性研究

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

采用非线性升力线方法和时间精确自由涡方法,对风切变条件下风轮的偏航气动特性进行了非定常数值模拟。为了改善非线性升力线方法的计算收敛性,提出了基于Newton-Raphson方法的环量方程迭代算法。建立了一种包含粘性涡核并由自由涡面和叶尖涡线构成的改进尾迹模型,可以提高尾迹的计算精度和效率。以NREL Phase VI风力机和Tj?reborg风力机为算例,分别对均匀风和切变风条件下、风轮处于不同偏航角时的气动力进行计算,并与测量值进行了比较。分析了风切变和偏航风对风轮气动特性产生影响的主要因素及风轮气动特性的变化规律。结果表明:计算方法可以有效模拟风切变条件下风轮偏航气动特性;在风切变条件下,偏航会增加叶片扭矩的波动,当风轮处于正偏航角时,叶片挥舞力矩的波动减弱,处于负偏航角时,挥舞力矩波动增强。

In order to study the aerodynamic conditions with shear wind, an unsteady numerical characteristics of HAWT rotor under yawed simulation method is developed. It consists of a nonlinear lifting line method and a time-accurate free vortex method. To improve the conver gence 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 effb ciency 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 mod- el. The NREL Phase VI and Tjmreborg 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 ana- lyzed. 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 fluctua- tions of shaft torque of blades are increased; the fluctuations of flap moment of blades are de- creased at the plus yaw angles and increased at the minus yaw angles.