尾缘涡街作用下三维流动对钝尾缘叶片气动载荷影响研究

Wind turbine blades with blunt trailing edges are advantageous to improve both structural and aerodynamic characteristics. However, there are problems due to the blunted trailing edges. The adverse pressure gradient in boundary layer and aerodynamic performance are changed by thick trailing edge; and, the thick wakes will evolve to Karman eddies in near wake region which leads to fluctuation of aerodynamic loads. They are great challenges to design this kind of blades. Therefore, an aerodynamic analysis method is put forward including a new 3D correction model and consideration of undulate aerodynamic parameters. The investigations are focused on 1) the influence on 3D flow by Coriolis force, 2) unsteady aerodynamic loads due to eddies shedding in the wake, 3) rotational correction model of blunt airfoils. The research will be carried out in steps as follows. At first, a numerical method dedicated to this kind of blades should be developed. Secondly, the performance of blade and aerodynamic parameters at representative locations will be measured at a medium-sized wind turbine. The CFD method is going to be verified by the experiment results. After finishing those two steps above, the flow field structure will be simulated, as well as boundary layer (including velocity profile, momentum thickness, transition, separation etc.) and the evolution of wake vortex street. The results are aimed to reveal the mechanism of 3D flow on blunt blades, interference of wake eddies and boundary layer, influence on unsteady loads due to shedding vortices. Furthermore, a unsteady aerodynamic analysis method is then developed by improving 3D correction model of blunt airfoils and adding the waved aerodynamic parameters of these airfoils. This investigation will contribute to improve the basic theories and design methods of large wind turbine blades with lower loads, weights and higher efficiency.

钝尾缘叶片具有良好的结构与气动特性，其尾缘厚度的增加导致边界层压力梯度变化，尾迹增厚脱落成涡街，非定常因素增加，气动参数偏离与波动等问题产生。为解决叶片设计中的以上问题，提出了依据三维非定常流动机理建立新三维修正模型并考虑气动参数波动的气动分析方法。主要研究：①柯氏力对三维流动的影响；②尾缘涡街导致的非定常气动载荷变化；③钝尾缘翼型三维修正。拟首先针对该类叶片研究数值求解方法；其次，采用基于中型机组的实验平台，测量叶片典型截面的气动参数，验证并改进数值方法；最后，模拟旋转运动中叶片的三维流场结构，边界层特征（速度型、动量厚度、转捩、分离等），尾涡演化等。拟达目标为：揭示三维流动机理，尾涡与三维边界层的相互影响，尾涡在叶片非定常气动载荷中的作用；改进钝尾缘翼型气动参数的三维修正模型；并据此建立专门针对钝尾缘叶片的非定常气动分析方法。结果对设计低载、轻质、高效大型风电叶片提供方法及理论基础。

钝尾缘叶片具有良好的结构与气动特性，其尾缘厚度的增加导致边界层压力梯度变化，尾迹增厚脱落成涡街，非定常因素增加，气动参数偏离与波动等问题产生。为解决叶片设计中的以上问题，主要研究：流动三维旋转效应；尾缘涡街导致的非定常气动载荷变化；钝尾缘翼型气动参数三维修正。研究过程中采用实验与数值模拟相结合的方法，对边界层特性及涡街特性进行深入研究，改进翼型三维修正模型，建立针对钝尾缘叶片的三维非定常气动分析方法。重要研究结果如下：（1）翼型三维气动性能与二维气动性能显著差异的主要原因是旋转产生边界层方程中的对流项、科氏力项及离心力项导致叶片根部存在明显的展向流动，使边界层厚度相对于二维条件下变薄。（2）采用LES及风洞试验方法研究钝尾缘翼型边界层及尾迹演化，揭示了钝尾缘翼型非定常气动特性与尾涡的关联性。表明产生翼型的非定常升、阻力特性的主导因素是卡门涡街的诱导。数值分析中捕捉到了边界层速度的宽频脉动，预示着转捩过程中伴随S-T不稳定性的发展。（3）通过实验研究，获得了大厚度钝尾缘翼型的边界层分离特性，发现了翼型失速附近流动分离不稳定性现象，并提出了流动控制方法。.尾缘涡街作用下三维流动机理、非定常气动分析方法的研究对提高钝尾缘叶片的性能及可靠性具有重要的学术价值。通过本项目的实施，不仅取得了预期结果，其中还发现了钝尾缘翼型的临界稳定性及翼型临近失速附近气动性能不稳定两个值得深入研究的科学问题。