基于多轴角运动模型的风轮非定常气动特性与三维流动研究

The flexibility of wind turbine blade and tower increase with the increasing of the wind turbine scale. The flap and lead-lag motions of the blade, and the forward-backward and side to side motions of the tower are getting more obvious. In addition, variable speed control, pitching and yaw are widely used in modern large scale wind turbine. The aeroelastic motions of the blade and tower, as well as the dynamic control of the wind turbine rotor, change the wind turbine rotor posture continually, enhancing the unsteadiness of the aerodynamic characters and three-dimensional flow of the wind turbine rotor. The conventional BEM and GDW methods cannot obtain the three-dimensional unsteady flow details, thus they cannot reveal the mechanism of the dynamic aerodynamic characters. The direct CFD/CSD coupling method is not mature enough to simulate the multi-body motions, and the computational cost is not affordable currently. The present project proposes a simplified model based on multi-axis angular motions. Both the aeroelastic motions of the blade and tower, and the active control motions of rotor are described uniformly using angular motions. This model will be validated using both CFD simulations and wind tunnel experiments. Then, unsteady CFD simulations are performed based on this model, to investigate the three-dimensional flow structure during the processes of yaw, uniform pitch, and variable pitch. The aim is to reveal the generation mechanism of dynamic inflow, turbulence wake due to multi-axis angular motions, and obtain the influence rules on dynamic characters of wind turbine, establishing the theoretical base for control strategies of pitch regulation and yaw for wind turbine.

随着风力机大型化，叶片和塔架柔性增加。叶片的挥舞摆振和塔架的前后左右运动明显。另外大型风力机普遍采用变速变桨和偏航等动态控制手段。叶片、塔架的弹性运动与风轮的动态调控使得风轮姿态不断改变，进而使风轮的气动特性和三维流动的非定常性显著增加。常规的叶素动量理论、涡尾迹法无法获得风轮附近的三维非定常流动细节，无法揭示风轮气动特性动态变化的机理；而直接CFD/CSD耦合计算对模拟多体运动尙存在困难，且计算量极大。本项目提出一种简化的风轮多轴角运动模型，采用角运动统一描述叶片、塔架的弹性运动和风轮的主动调控运动。通过CFD模拟和风洞实验对该模型进行评估。并将该模型与非定常CFD模拟结合，分别研究偏航、统一变桨、独立变桨等过程中风轮三维绕流场的演化过程，揭示多轴角运动引起的动态入流、湍流尾迹等现象的产生机理，总结多轴角运动对风轮的动态特性的影响规律，为风轮的气动设计和控制策略的制定提供理论依据。

风电是我国大力发展的可再生能源。叶片是风电机组吸收风能的关键部件。风电机组大型化使得风力机叶片和塔架的柔性增加，产生多自由运动。对于海上风电机组，由于风浪耦合作用与平台运动，风电机组的多自由度运动更加。另外，大型风电机组普遍采用变速变桨和偏航等动态控制手段。风力机叶片、塔架和平台的多自由度运动与风轮的动态调控共同作用下，风轮姿态不断改变，其气动特性和三维非定常绕流的复杂性显著增加。常规的叶素动量理论、涡尾迹方法无法获得风轮附近的三维非定常流动细节，无法揭示风轮气动特性动态变化的机理。另一方面，基于CFD/CSD的流固耦合方法对多体运动的模拟存在网格处理困难、计算周期长、计算量巨大的问题。本项目提出一种简化的风轮多轴角运动模型并进行研究，采用角运动统一描述叶片、塔架的弹性运动、平台运动引起的风轮运动和风轮的主动调控运动，创新地提出了采用双滑移和多滑移方法处理多轴角运动，对风电机组的动态偏航过程、海上风电机组多自由度运动过程进行了模拟研究，通过CFD模拟和风洞实验对该模型进行评估。并对叶片分离流动的控制方法进行了研究。通过与实验和其他方法计算结果的对比验证了多轴角运动模型，得到了以下结论：短时间的偏航启停过程会加大风电机组的整体载荷；平台纵摇运动加剧了风电机组总体功率、推力的输出波动；涡发生器和零质量射流流动控制技术可以增强风轮的风能捕获能力，提高功率系数；叶片的旋转周期对会使得机舱尾部速度增大。对于风电机组多轴角运动规律的总结和动态响应的研究，为大型风电机组的设计和控制策略提供理论依据和数值参考。