后掠型风力机叶片气弹耦合特性与颤振发生机理研究

The backward swept blade is a new type of smart blade formed by stacking airfoils along a line curved towards the trail edge in the rotor plane, and it has the functions of self-adjustment and load alleviation. In this project, the aeroelastic coupling characteristics and instability mechanism of bending-torsional flutter of the swept blade will be analyzed mainly by investigating its aeroelastic coupling mechanism. By applying the theoretical analysis and numerical simulation, the three-dimensional flow field characteristics will be studied. Based on the vortex method, the lifting surface model will be developed, which is suitable for analyzing the dynamic aerodynamic loads and aeroelastic coupling of blades with backward swept aerodynamic configuration. Both the swept blade aeroelastic coupling among the aerodynamic, elastic and inertial forces and the mechanism of its feedback on the aerodynamic forces and flow field will be explored using the theories of multi-body system dynamics and nonlinear vibrations of structures. The variation rules of each vibration mode of the swept blades for wind turbine units under different operating conditions, especially the coupling between the blade flapwise and torsional modes, will be studied based on the time-domain response of aeroelastic coupling. The phase evolution characteristics of the aerodynamic forces and bending-torsional deformation and the changing rules of aeroelastic damping of bending-torsional mode will be deeply investigated to reveal the formation mechanism of the bending-torsional flutter mode and the effect of blade backward sweeping on the bending-torsional flutter. The research findings will provide theoretical basis and analysis methods for the independent design and the safe and stable operation of a new generation of the backward swept blade.

后掠型叶片是叶片外展段积叠线在旋转平面内向尾缘方向弯曲的一种具有自适应、自卸载功能的新型智能叶片。本申请项目拟以探索后掠叶片气弹耦合机制为主要途径，研究该类叶片的气弹耦合特性及其弯扭颤振失稳机理。采用理论和数值模拟相结合的方法，研究后掠叶片的三维流场特征；应用涡旋线方法，开发适用于该类型气动布局的动态气动载荷与气弹耦合分析的升力面模型；结合多体动力学理论和结构非线性振动理论，研究后掠叶片在气动力、弹性力和惯性力作用下的气弹耦合特性，及其对叶片流场和气动载荷的反馈机制；结合气弹耦合时域响应，研究后掠叶片各阶振动模态随机组运行工况的变化规律，特别是挥舞与扭转变形模态间的耦合；围绕气动力与弯扭变形间的相位演化以及弯扭模态气弹阻尼变化规律，揭示弯扭颤振模态的形成和叶片后掠对弯扭颤振的影响机制。研究成果将为新一代后掠叶片的自主设计与安全稳定运行提供理论基础和分析方法的支撑。

本研究项目主要研究后掠型风力机叶片的三维流动特性与气动载荷的演化规律，从而更准确预测叶片非线性的弯曲与扭转耦合变形及其对气动载荷的反馈，以及结构的弯扭和气弹的耦合对颤振失稳特性的影响等。是涉及动态气动特性与结构非线性动力学的跨学科研究。.在本课题的研究中，引入了两种能反映结构几何非线性的动力学建模方法，即基于多体动力学理论的修正的超级单元(Super-element)模型和绝对节点坐标方法。两种建模方法均能较准确地描述后掠叶片的几何非线性变形及其动力学特性。建立了基于螺旋尾涡升力线模型的水平轴风力机风轮气动性能分析算法，结合开发的非线性结构动力学模型建立了后掠叶片气弹耦合动力学方程，及其数值求解算法，实现了后掠叶片气弹耦合响应分析。.基于有限元数值模拟，研究了后掠叶片这种外形与内部结构较复杂构件的弯扭耦合特性；然后考虑到后掠叶片变形的非线性效应较为显著，为了更好地展现其非线性效应，基于多体动力学理论，结合其变形和运动的特点，实现后掠风力机叶片气弹耦合响应时域分析、性能分析和动力特性分析。对后掠叶片的弯扭耦合特性和降载增效机理进行了定量研究。.应用牛顿-欧拉方程建立叶片非线性结构动力学方程，结合修正的B-L动态失速模型进行分析。通过将气弹耦合模型在叶片变形平衡状态的线性化，构建柔性叶片气弹模态分析特征方程及其数值求解方法，实现柔性叶片气弹模态分析。在考虑柔性叶片气弹耦合响应与系统振动模态参数基础上，通过求解得出叶片的气弹响应，结合模态叠加理论，计算气动力在各阶模态下所做的功，得出叶片的模态气动阻尼。实现了后掠叶片颤振产生机理和颤振边界的确定。.通过本研究，形成了涉及叶片流场三维流动和结构非线性振动相互耦合的后掠叶片气弹耦合与弯扭颤振分析模型，并实现了相应的数值算法，为新一代被动降载后掠型叶片的自主设计提供理论和分析方法的支撑。