【作者】 陈洪胜；

【导师】 徐建中； 石可重；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2012， 博士

【摘要】 后掠型风力机叶片是翼型沿着向尾缘弯曲的积叠线造型而成的一种新型智能叶片。现有研究表明风力机后掠叶片在保证功率输出的同时可以显著降低叶片的推力载荷,这为降低风力机生产制造成本,提高风电生产的经济竞争性提供了一条有价值的途径。当前对后掠叶片的研究主要还是围绕气弹问题展开的,对于更为基础的气动研究开展较少,后掠对叶片绕流的影响机理有待深入探索。本文从叶片的气动性能、流动分离特性等角度研究了这种叶片造型方式的影响,并分析叶片后掠造型中几何参数如后掠的起始位置、后掠角等的影响。本文研究了叶片后掠对风力机叶片三维流场的影响。通过对NREL PhaseVI直叶片及其后掠改型叶片进行三维CFD数值计算,比较叶片经过后掠造型前后的功率输出,发现后掠叶片在低风速下比原型直叶片略小,而由于失速延迟作用在较高风速下超过了原型叶片的出功,但在高风速下两种叶片都出现大分离时,后掠叶片的功率输出现更大下降；对比叶片表面极限流线可见后掠叶片流场的三维流动效应更加显著,具体表现为在后掠叶片吸力面前缘处流动向叶轮中心偏转,而在尾缘附近则向叶尖方向存在更显著的偏转,这一点在流动分离情况下变得更加显著。叶段绕流与截面翼型压力场分析表明,科氏力、离心力及附壁效应等三维因素减小了后掠叶片截面翼型的吸力峰,同时抑制失速,从而导致叶片气动性能的上述变化。接着,从后掠对叶片流动分离的影响及叶片截面的二维流动两方面深入研究了三维因素影响叶片绕流的机理。针对后掠叶片的流动分离特性,本文探讨了后掠对流动分离的影响。与当地翼型的二维流场流动分离点进行比较,显示后掠叶片三维流场的流动分离点在一定程度上出现了向尾缘的推迟。但是与直叶片三维流场的流动分离点进行比较,在流动分离区,叶片的后掠使流动分离点向前缘靠近,降低了叶片的气动性能,揭示了后掠流动分离失速后气动效率急剧下降的机理。此外,可以看到,利用二维BEM模型对后掠叶片进行分析需要引进合适的三维失速延迟修正模型,而目前为止适合于后掠叶片的三维失速延迟模型并不存在。以三维计算流体力学求解所得流场结果为基础,研究了后掠对截面翼型二维主流方向流动的影响。通过壁面环量法分析了沿叶片展向截面翼型的入流,获得了截面翼型来流攻角的分布,将多个后掠改型叶片与原型直叶片进行比较,结果显示后掠对叶片展向的攻角分布影响较小,叶片的后掠主要通过三维效应影响当地翼型的压力分布来降低叶片气动载荷。最后探索了后掠几何参数对叶片主要气动特性的影响规律。由于需要考虑的因素较多,采用正交分析的方法设计了一组后掠改型叶片,并对其进行了数值模拟分析。直叶片与后掠叶片的推力系数对北表明,由于后掠减小了截面翼型的吸力峰,从而减小了压力面与吸力面的压力差,使得即使不考虑气弹耦合作用后掠叶片仍能够降低推力载荷。在此基础上,对影响后掠外形参数的因素进行极差分析,结果表明影响后掠叶片功率系数和推力系数的主要因素为后掠起始位置与当地后掠角。对比各因素水平下的总体气动参数的平均值显示各因素对叶片的气动性能的影响存在一定规律,这为后掠叶片的气动设计提供了理论依据。更多还原

【Abstract】 The aft-swept wind turbine blade is a new type of smart blade formed by stacking airfoils along a line cured towards the trailing edge. It has been demonstrated to be able to dramatically reduce the thrust loads on the turbine while keeping the output power. Which means that the aft-swept blade provides promising approach to save the manufactural cost of wind turbine blade and make wind power more competitive in the financial aspect. However the aerodynamic characteristic of the swept blade is seldom studied especially the corresponding flow mechanism is not completely clear now. Therefore it is necessary to analyze the detailed flow field structure and separation characteristics of the swept blade from the special geometry parameters of the swept blade, such as the starting position of sweep and the local sweep angle etc.The swept blade can dramatically affect the aerodynamic of wind turbine. From the power comparison of NREL Phase VI straight blade and the corresponding swept one, computed by Computational Fluid Dynamics (CFD) method, we can see that:(1) at low wind speed, the output power of the swept blade is slightly less than straight blade;(2) when wind speed increases, the swept blade exhibits more stall delay char-acteristic and obtain higher power;(3) at high speed, when the flow are both separated, the aerodynamic performance of the swept blade decreases evidently. After deep anal-ysis on the three-dimensional (3D) flow filed, it was demonstrated that the span wise flow is speed by the swept profile, as the flow at the suction side around the airfoil leading edge slightly turn toward the rotating center and the flow at the suction side on the trailing edge is dramatically bending to the blade tip direction, which is greatly en-hanced at the flow separation condition. Further analyzing of the pressure distribution of local airfoil shows that the character of swept blade is mainly due to the influence of the centrifuge force, Coriolis force, Coanda effects and the interaction between them.For the separation aspect, comparing the local flow field of2D airfoil and3D swept blade, it can be seen that due to rotation the separation point of the3D swept blade is nearer to the trailing edge. But this condition is different when comparing the flow field of the swept blade and straight blade. This means that the swept blade has less stall delay effect than the straight one and this is not good for the load reduction of the swept blade and this is the why the swept blade has a poorer performance at deep separation.For the main flow aspect, based on the3D CFD results and using the wall cir-culation method, we analyzed the2D local flow field along the span of the swept and straight blades and obtained the inflow angle of attack (AOA). Comparing the flow fields, little difference of the AOA distribution between the swept and the straight blades was observed, and for the swept blade the reduction of load is realized from the change of the local pressure distribution.At last, the aerodynamic quality of the swept blade influenced by its geometry parameters is analyzed. Considering the complex geometry parameters of the swept blade may have an influence on the aerodynamic performance and the operation state of the wind turbine, we designed an orthogonal test, in which a group of swept blades has been included which has different geometry characteristic. Then the aerodynamic performance of these blades are computed by CFD. From the comparing of the thrust coefficients we can see that because the pressure difference between the suction side and the pressure side is reduced by Coanda effects, the swept blade can reduce the thrust load even not considering the excellent aeroelastic performance of which. Mak-ing range analysis of the geometry parameters describing the swept blade, we can see that the power coefficient of the swept blade is dramatically influenced by the starting point of the sweep and the local sweep angle. From the comparing the average aerody-namic performance influenced by these different geometry parameters it can be seen that the influence of the geometry parameters obey some certain rules, which provides the theoretical basis for the design of swept blade.更多还原