大型钝尾缘层流叶片水平轴风力机风能吸收机理研究

Modern horizontal axis wind turbines are developing towards large scales. As the key component of wind turbines, rotor blades capture wind energy and use it to drive the generator. Thus, their aerodynamic and structural characteristics are particularly important for the wind turbine designs. Blades whose airfoil sections have blunt trailing edges can effectively improve the structural stiffness and to a certain extent, also improve the aerodynamic performance of rotor blade. In recent years, the design of such airfoils for large wind turbines has attracted more and more attention and becomes a popular subject. In addition, the transition from laminar to turbulent flow on rotating blade surfaces plays an important role in determining the overall aerodynamic performance of a horizontal axis wind turbine. In this project, the aerodynamic properties of laminar-flow airfoil used on wind turbines will be studied and special attention will be given to the physical mechanism at work in the change from laminar flow to turbulent flow around the surface of the airfoil. The influence of modification with a blunt trailing edge on the airfoil aerodynamic characteristics and the characteristics of wind power will be investigated at first. Then, the energy absorbing mechanisms of large horizontal axis wind turbines installed with laminar blades including blunt trailing edges will be studied in depth. Based on the Reynolds averaged Navier-Stokes equations, transition models will be adopted to simulate the flow over an airfoil and thus the three-dimensional and rotational flow field of the wind turbine model can be analyzed in detail. The effects of blunt trailing edge design on the change in properties of the flow around the turbine blades will also be analyzed. In a wind tunnel experiment, measurements of the velocity field in the boundary layer on the airfoil surface and wake flow of the airfoil will be performed by using laser-based particle image velocimetry system and subsequently, comparison of the lift and drag characteristics for the baseline and the modified airfoils will be conducted. At last, based on the results obtained from both simulations and experiments, the internal flow mechanism of blunt trailing edge modification can be revealed, with the aim of providing theoretical and technical support for the design of large wind turbine blades with improved aerodynamic performance.

现代水平轴风力机朝着大型化的方向发展，叶片作为整个风力机的关键部件，其气动性能与结构特性在风力机设计要求中显得尤为突出。叶片采用钝尾缘翼型可以有效提高其结构刚度并在一定程度上改善其气动性能，近年来在大型风力机气动设计中受到越来越多的关注。此外，叶片表面从层流到湍流的转捩也对风力机气动性能有着重要影响。本项目针对风力机层流叶片，考虑叶片表面流动转捩，分析不同来流条件下钝尾缘改型对二维翼型气动特性和整个风力机功率特性的影响，研究安装钝尾缘层流叶片的大型水平轴风力机的风能吸收机理。采用基于雷诺平均的转捩模型对翼型绕流和风力机三维旋转流场进行数值模拟研究，分析钝尾缘设计对流场细节的变化；采用粒子图像测速仪对翼型表面边界层流动和尾迹流进行风洞实验研究，并对比原始翼型和修改翼型的升阻力特性。最后综合数值和实验两方面研究结果，深入揭示钝尾缘改型的内在流动机理，从而为大型风力机叶片设计提供理论和技术支撑。

现代大型水平轴风力机对于叶片的设计要求是既要具有良好的气动特性又要满足结构方面的刚度要求。在风力机叶片翼型设计过程中，层流翼型结合钝翼型设计可以有效提高叶片的结构刚度并在一定程度上改善叶片的气动性能，本项目基于这一学术思想开展了一系列的研究工作。本项目主要研究内容如下：.(1) 基于NACA 6系列尖尾缘层流翼型，采用多目标优化设计方法得到新系列钝尾缘层流翼型，新系列翼型相比同厚度的FFA系列翼型具有更大的尾缘钝化厚度，并且在设计攻角下具有更大的升力系数和升阻比，可以考虑作为大型水平轴风力机叶片的设计翼型；.(2) 本项目采用的翼型多目标优化设计方法在进行翼型气动优化设计时综合考虑了翼型在设计攻角和非设计攻角下升力系数和升阻比特性以及翼型失速特性，优化后得到的新系列翼型通过完全CFD方法对其进行了气动性能验证。CFD计算结果表明，这类新设计的翼型总体上具有较好的气动性能。本项目采用的针对风力机翼型多目标优化设计方法有望在其他领域翼型气动设计中得到进一步应用；.(3) 对于翼型表面粗糙度效应的分析，本项目提出两种CFD流动仿真策略，布置单个矩形凸台和多个分布式三角形锯齿粗糙元，通过不同翼型的CFD模拟说明了这种流动仿真策略的可行性，该仿真策略有望替代风洞实验中关于叶片表面粗糙度效应的分析方法；.(4) 对于实际风力机运行过程中出现的叶片动态失速效应以及叶片表面的粗糙度问题，本项目采用基于转捩的RANS方法研究了不同粗糙翼型的动态气动特性，并考虑采用一种在翼型吸力面布置可摆动襟翼的方法来缓解翼型的动态失速效应；.(5) 将优化后的钝尾缘层流翼型用于实际风力机叶片设计，通过三维旋转风轮流场CFD模拟与分析，说明了钝尾缘层流翼型在实际风力机叶片设计中的应用可行性。