摘要
随单机容量的增加,风力机向大型化柔性化的趋势发展,特别是弯扭叶片的应用,使风力机各部件间的耦合振动变得更加剧烈,其气弹问题也变得更为复杂。针对于此,本文首先对气动模型进行研究,以获得准确的气动力；然后,从弯扭叶片固有特性分析耦合机理,以此为理论依据,最终建立了一种新的风力机多体动力学模型,进行气弹分析,主要完成了以下研的研究工作如下：
第一,研究BEM理论及修正算法发现,诱导因子对计算结果的影响较大。分析现有算法的优缺点,通过挥舞力矩和低速轴转矩的比较,结合气弹应用,指出适用的算法,保证了为气弹模拟提供准确的气动力。
第二,根据弯扭叶片的结构特点,应用空间曲梁理论,建立了一种新的直—曲混合梁有限元模型,编写程序对1.5MW实例叶片进行计算。结果表明,弯扭叶片的每阶模态,均有耦合现象,只是低阶模态下,并不十分明显,而随着频率阶次的增加,耦合振动逐渐增强。这是由动力学方程的质量矩阵和刚度矩阵中的耦合项所导致,而耦合项的产生是因为模型建立时考虑了弯扭因素。因此气弹计算中需要考虑挥舞、扭转、摆振各方向的自由度。并应用此程序对叶片中梁帽质量分布进行优化,结果表明质量不变,较少叶尖质量,可提高叶片频率,为铺层设计提供参考。
第三,依据上述结论,耦合特性不可忽略,作者提出应用球铰约束,建立新的旋转叶片多体动力学模型,开发计算程序,并验证程序的正确性。而后采用弱耦合方法,结合BEM程序,对实例叶片在额定转速,恒定均匀风速情况下,进行气弹响应模拟。与FAST软件比较,结果表明,由于叶片耦合变形影响,使挥舞方向上气弹响应变小,摆振方向响应变大。这点为预弯叶片的设计提供了参考。此模型为整机模型建立打下基础。
第四,针对风力机结构的特点,将其简化为由叶片、轮毂、机舱、塔架四部分组成的机构,建立整机多体动力学模型。参考公开的整机参数,结合本文实例叶片,进行气弹模拟。与FAST软件比较,结果显示,对于本文算例,在无偏航无变桨情况下,稳定均匀风速时,叶片挥舞方向响应变小,摆振方向响应变大,机舱所受载荷降低,塔架响应变小,这些变化均是由于模型中考虑叶片的耦合特性。对整机设计具有参考价值。
第五,针对实例叶片设计了实验方案,利用中科院工程热物理所与保定国家新能源产业基地合作建立的风电叶片检测台进行全尺寸实验,结果表明,扭转模态确已在低阶模态中出现,且叶片各阶模态均有耦合变形,从而验证了作者提出的混合梁有限元模型。
The modern blade becomes more large and flexible with bending-twist shape. Therefore, it's natural coupling dynamics becomes more complex, and more serious coupling with wind turbine, that will cause aeroelastic damage more easily. So the wind turbine aeroelastic research is very important. A new finite element model is established to study the natural coupling mechanism of bending-twist blade. And then, a new multibody dynamics model is built for aeroelastic analysis based on the the mechanism. The following research works have been finished.
Firstly, aerodynamic program is written on the study of BEM theory and its correction algorithm. The advantages and disadvantages are compared on the induced factor algorithm. The results show that different algorithm has great influence on BEM computation. Then a new algorithm for induced factor is developed. With comparison to the experiment, this new algorithm is more accurate. This will help the next aeroelastic computation.
Secondly, A new finite element model is established according to the bending-twist shape with special curved beam theory. And then, the coupling character of a1.5MW blade is studied. Compared to straight beam theory, the results show that twist mode has been appeared in low frequency, and this make the coupling deflection of flap、edgewise and twist. Therefore the twist factor must be accounted for aeroelastic simulation.
Thirdly, According to the above conclusion, a new multibody dynamics model is built with spherical hinge. Aeroelastic response of the1.5MW blade is simulated with aerodynamics from BEM program. The results show that the coupling response deflection is more serious for the twist deflection. That makes the flap response reduce and edgewise response increase. And this is advantageous for bending design. Also, this is the base of the wind turbine model.
The fourth, accounting for twist deflection, the wind turbine multidynamics model is established based on the above blade model. The aeroelastic simulation results show that, for the example in this paper, with stable wind, torsional deformation cause leaf root waving pendulum vibration reduced, smaller tower response without yaw and pitch control. This has reference value for wind turbine design.
The last, the full-scale blade experiment is done with the test bench built by Institute of Engineering Thermophysics and Baoding national new energy base. The results verify the above curved blade theory.
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