【作者】 沈昕；

【导师】 杜朝辉； 竺晓程；

【作者基本信息】 上海交通大学 ， 动力机械及工程， 2014， 博士

【摘要】 叶片是水平轴风力机的核心部件，可将风能转化为机械能。叶片的气动性能不仅直接决定风力机的能量转换效率，还影响风力机及其部件的运行可靠性。风力机运行在自然环境中，由大气湍流、风剪切以及阵风等引起的流动不稳定性，同时由叶片、塔架等部件的气动-结构耦合问题进一步增加了叶片流动的复杂性。建立具有明确物理意义，准确高效的风力机定常/非定常气动性能的预测方法，不但可为风力机叶片设计和控制策略确定提供基础数据，也是具有重要学术价值的研究工作。本文基于升力面涡方法，建立水平轴风力机叶片定常与非定常工况下气动性能的预测模型，在此基础上构建可计及弯掠三维形状的风力机叶片气动优化设计平台，以及独立变桨控制策略的气动分析方法。具体研究内容如下：1.建立空间迭代自由尾迹数值计算方法，结合升力面法编制能预测风力机在定常和准定常工况下气动性能的计算程序。数值研究了风力机在正对来流及不同偏航角工况下的尾迹空间结构，成功地捕捉到叶尖涡发展的基本特征，准确预测风力机在正对来流时叶尖涡的膨胀过程及叶尖涡在不同偏航角下的偏转角变化趋势。在低风速及较小偏航角工况下，气动性能预测结果与实验值吻合较好。2.在采用空间迭代自由尾迹的升力面模型准确预测出风力机在定常及准定常工况下的气动性能的基础上，详细分析了具有弯掠三维形状的叶片对风力机气动性能的影响。弯掠叶片通过改变叶尖涡和叶片主体的相对位置影响叶片上的径向环量分布，进而改变风力机气动性能。3.建立时间步进自由尾迹数值计算方法，改进了计算的稳定性，结合升力面法，建立能预测更为复杂非定常工况的风力机气动性能计算程序。分别预测了桨距角突变，塔架影响，风剪切等工况下的风力机的气动性能，并研究了独立变桨时的气动特性。4.利用时间步进自由尾迹的升力面模型，在桨距角突变过程中准确获得具有下冲与过冲特征的风力机非定常气动性能。发现脱落涡对风轮上的气动性能影响的时间尺度较短，其数量级为c/Ωr级别，近场尾迹和叶尖涡达到新的平衡状态所需时间尺度较大，其数量级为。5.通过引入塔架对上游和下游流场影响的模型，采用时间步进法预测了塔架对上风向和下风向风力机的气动性能的影响。叶片经过塔影区域时输出功率和载荷有所下降，并在相位角上存在滞后效应，塔影对下风向风力机的性能影响波动幅值更大，风力机在偏航工况下运行时，风力机受塔架影响更为明显。6.采用时间步进法，研究了风剪切对风力机风轮的气动性能的影响，类似偏航，在周向呈现周期性变化的趋势。并对独立变桨技术在风剪切工况下应用的气动特性进行了分析，认为该技术能有效减小叶片根部挥舞力矩、风轮偏航力矩和俯仰力矩波动幅值。7.建立可实现不同优化目标的风力机优化设计平台，分别以风力机年发电量、低风速启动性能等为设计目标对一款600W小型风力机进行优化设计。建立了多目标风力机优化设计平台，采用基于Pareto最优解概念的多目标优化算法，采取先优化后决策的方式对NREL PHASE VI风力机叶片进行多目标优化改进。更多还原

【Abstract】 As one of the most important key parts of horizontal axis wind turbines, therotors not only extract energy from wind but also transfer loads to other parts. Theaerodynamic performance of the rotors has a main influence on the quantity of thepower output and the reliability of almost all parts of wind turbines. Theaerodynamics of a wind turbine is extremely complicated. Such problems include thechallenges in understanding and predicting the unsteady blade air-loads and rotorperformance under complicated environmental effects that may affect the air-loads ona wind turbine, as well as the predicting the dynamic stresses and aero-elasticresponse of the blades due to the increasing size of the wind turbines. It has greatvalue not only in engineering applications but also in theoretical research to setupreliable, precision and efficient tools to predict the aerodynamic performance ofHAWTs under both steady and unsteady conditions.In this thesis models are established for the purpose of predicting theaerodynamic performance of HAWTs under both steady and unsteady flow conditions,by which the influence of3D geometry effects and the aerodynamic responses subjectto the complicated effects such as wind shear, tower shadow, pitching motion andindividual pitch control are studied. Following are the main work and findings of thisresearch project:1. A lifting surface method based on a relaxation free wake model is developed and aerodynamic performance of HAWTs under steady flow condition is studied. The relaxation free wake model can capture the main characters of the distortional wake such as the expansion ratio under both axial flow and yawed flow condition and the skew angle of the wake under yawed flow condition.2. The numerical predictions based on the lifting surface method with the relaxation free wake model under rated and low load working conditions show good agreement against the experiment data. The effects of dihedral and sweep3-D shape on blade aerodynamic performance are studied. The aerodynamic results analysis show that the3-D shape has a major influence along the blade due to the changing the relative postion between the blade and the tip vortex.3. A lifting surface method based on a time marching free wake model is developed. A new backward difference scheme is deduced. The linear stability analysis shown that the new scheme is stable for all values of time discretization. The aerodynamic performance of HAWTs under unsteady flow condition such as pitching motion, tower shadow, wind shear and individual pitch control are studied.4. The numerical predictions based on the lifting surface method with the time marching free wake model under pitching step motion show excellent agreement with the measured results. There are two stages during the entire dynamic inflow process. The first stage, the sudden change of the angle of attack due to the blade pitch motion leads to the instantaneous change of the torque which has a slight delay compared to the pitch motion. At this stage the shed vortex plays an important role and its influence has a very short time scale in the order of c/Ωr. The second stage is the recovery stage. The second stage is the induced velocity caused by the shed vortex go wake and the induced velocity caused by trailed vortex take the main part of the whole induced velocity. At this stage the trailed vortex is a mixture of the ‘new’ and ‘old’ vortex and an end with the ‘old’ vortex has travelled away from the rotor and the ‘new’ vortex takes the dominant influence to the induced velocity. Then the rotor goes into the new equilibrium. This stage takes place with a longer time scale in the order of.5. The influence of the tower shadow to both upwind and downwind rotor are studied. It is shown an impulsive response of the blade loading when the blade is passing through the tower shadow region, the reason of which is that the ‘sharp’ velocity gradient at the tower shadow region. Compaered to the unyawed flow condition the tower shadow has a wider influence region to the rotor in yawed flow.6. The aerodynamic performace of the wind turbine working under wind shear flow is studied which is shown that the wind shear flow has a periodic influence to the rotor. Then the individual pitch control technic is used to improve the performance of the wind turbine under sheared flow condition. It is an effective active control system that not only aims at good quality power control but also focuses on the reduction of fatigue relevant loads on the turbine component caused by wind shear, tower shadow and turbulence.7. A general procedure of multi-objective optimization of wind turbine blades with sweep and dihedral3-D shape is proposed in this thesis. A600W type small wind turbine is designed which takes the AEP, starting performance and blade mass as objectives. Two objectives the AEP and thrust of the rotor are optimized bases on the NREL Phase VI rotor blade using the NSGA-II algorithm as the optimization algorithm which can provide the Pareto optimal front of conflicting objectives.更多还原