【作者】 俞国华；

【导师】 杜朝辉； 竺晓程；

【作者基本信息】 上海交通大学 ， 动力工程及工程热物理， 2013， 博士

【摘要】 水平轴风力机是最有效的风能转换装置，在其开发和研制过程当中，最关键的核心问题就是设计高效、高可靠性的风轮。随着风力机的尺寸逐渐增大，需要更可靠的气动载荷预测方法，来确保更加优化的设计。气动载荷的可靠预测必须依赖准确的工程计算方法、气动力模型和修正模型。这些方法及模型的准确性又取决于对静态失速（失速延迟）、动态失速及动态载荷等关键气动问题所涉及的复杂流动机理的正确认识和深刻理解。本文通过数值计算和理论分析，研究了风力机静态失速和动态失速等气动问题，提出了一种基于代理的递归框架的非定常气动力降阶模型，采用了合成射流的方式对风力机翼型进行了主动流动控制的研究。研究以具有丰富详实的实验数据的美国国家可再生能源实验室的联合实验风轮和经典翼型为应用对象。研究成果有助于建立较为准确的载荷预测模型，提高风力机的设计水平，为保障风轮的可靠运行和提高风力机整体性能提供有力的支持。本文主要研究内容和研究成果如下：1）采用Menter的带转捩修正的K SST湍流模型，成功地对不同来流速度下的典型的NREL Phase VI风轮的内部流场进行了模拟，总体上和实验值吻合较好，只是在较高的风速下，流动分离严重，存在一定的差异，验证了计算的准确性。通过叶片不同叶高截面处的压力系数分布以及叶片吸力面的极限流线分布详细分析了叶轮流场特性。2）基于风轮的全尺度数值模拟结果，分析了失速延迟的内在流动机制，建立了三维流场和工程模型间的联系。推导获得了风轮不同叶高位置的轴向诱导因子，确定了各位置的有效攻角，提取了包含三维旋转效应及叶根叶尖效应的截面翼型气动数据。并与Du-Selig失速延迟模型的结果以及Tangler方法得到的结果进行了深入的比较和分析，探索了实际叶片不同叶高位置的失速特征。3）通过数值方法分析了典型深度失速工况的流场特征和动态失速涡的发展、传播和最后脱落的过程，加深对动态失速发生机理的理解。基于Menter的转捩修正的k SST湍流模型及网格变形的动网格技术对绕其1/4弦长点作正弦波周期性振荡的风力机翼型进行了CFD模拟，并与风洞测试的非定常实验结果进行了全面的对比，表明两者基本吻合，验证了动态失速数值模拟结果的准确性。通过流线分布和压力系数分布，揭示了气动力迟滞回线的变化特征。4）基于所获得包括未失速、失速初生到轻度失速以及最后的深度失速多个工况下的非定常流场数据，研究了不同折合频率、平均攻角以及振荡幅角对翼型动态失速的影响。折合频率对动态失速有着重要的影响，随着折合频率的增大，升力的峰值出现在更高的攻角处，迟滞效应变得更为显著。在某些工况中，导致负的气动阻尼和迟滞现象加剧。并且基于升阻力和转矩系数，分析了动态失速对实际运行的风力机载荷的影响。5）基于以上的翼型非定常数据，利用SBRF降阶建模方法，有效地预测了动态失速条件下翼型的非定常升力，阻力和转矩。研究证明，对气动响应求解要求逼近精度较高的诸多气动弹性以及被动/主动最优化设计研究中，SBRF降阶模型是一种非常理想的既保留极高近似精度又具有较高计算效率的非定常气动模型。6）采用合成射流，对静态及振荡的风力机翼型绕流流场进行了流动控制效果的数值研究。研究发现：对于静态翼型，在小攻角流动附着时，对翼型的性能则有负面的影响，在预失速阶段，合成射流对翼型性能有显著的提升效果，在过失速区域则影响微弱。对动态振荡翼型，合成射流在翼型振荡周期很大范围内能够有效抑制动态失速条件下的气动力迟滞效应，但是对于深度失速时有限的大攻角范围内，仍然存在强烈的涡脱落及气动力振荡。更多还原

【Abstract】 Designing highly efficient and reliable wind turbine rotor is the most essentialproblem in the research and development of horizontal axis wind turbine (HAWT) whichhas been the most effective wind energy convertor. With the radical increase in windturbine scale, to ensure more optimal designs, more reliable predictions of aerodynamicloads which depend on the use of accurate engineering computational methods,aerodynamic modeling and correction models, are needed. The accuracy of these methodsand models however relies on a correct cognition and a profound understanding in thecomplicated flow mechanisms that are closely related to key aerodynamic problems suchas static stall (stall delay), dynamic stall and dynamic loads etc.Through numerical computations and theoretical analysis, static stall and dynamicstall problems on wind turbines are investigated, a reduced-order model for unsteadyaerodynamic forces prediction based on a surrogate-based recurrence framework (SBRF) isput forward, and a study on the impact of active flow control with synthetic jet on a windturbine airfoil is performed. The research is based on the combined experiment Phase VIrotor and S809airfoil of National Renewable Energy Laboratory (NREL) for which thereare abundant specific and detailed experimental data available. The research achievementshelp establish more accurate loads prediction models and enhance wind turbine designlevel, which provides a strong support for ensuring wind turbine operation reliability andenhancement of its overall performance.The main contents and achievements of the research are as follows:1) Using Menter’s transition corrected k SST turbulence model, numericalsimulations of the flowfield around the typical NREL Phase VI rotor under differentfree stream speeds is carried out, and the result are generally in agreement with the experiments with some discrepancy under high wind speed when the flow separationincreases and the accuracy of simulation is validated. The rotor flow field features areanalyzed in detail with pressure coefficient distribution on different blade radialsections and the limiting streamlines distribution on the blade suction surface.2) Based on the full scale rotor CFD results, the intrinsic flow mechanisms of stall delayis analyzed, and the relations between3D flow field and engineering models isestablished. The axial reduction factors at different blade radial sections are deduced,and the effective angles of attack are obtained. The sectional aerodynamic coefficientswhich include3D rotational effects and blade tip and root effects are extracted.Extensive comparison and analysis is performed among CFD results, those withcorrection by Du-Selig stall delay model and those of Tangler Method, and the stallcharacteristics of different blade radial sections is explored.3) Through numerical simulations, the process of dynamic vortex development,convection and finally shedding into wake for a typical deep stall case are illustratedin detail leading to a further understanding of the mechanism involved in the dynamicstall phenomenon. With the application of Menter’s transition corrected k SSTturbulence model and mesh deformation based dynamic mesh technique, CFDsimulations on the wind turbine airfoil undergoing sinusoidal periodic pitchoscillations about it’s quarter chord point are carried out. The result is compared withthe wind tunnel experimental data, which shows a good agreement, thus the accuracyof CFD simulations is validated. Via streamlines and pressure coefficient distribution,the variation of aerodynamic hysteresis loops is disclosed.4) Depending on the unsteady flow field data of the multiple cases under non-stall, stallonset, light stall and deep stall conditions, the impact of reduced frequency, meanangle of attack and the amplitude of pitch oscillation on the airfoil dynamic stall isinvestigated, which finds that reduced frequency plays a great role in dynamic stall.With increased reduced frequency, lift peak value is to appear at a higher angle ofattack, and the negative aerodynamic damping and hysteresis effect become morepronounced in some cases. Based on the lift drag and moment coefficients, theinfluence of dynamic stall over wind turbine practical operation is analyzed.5) Based on the above computed airfoil unsteady aerodynamic results, with SBRF reduce-order modeling, the unsteady lift, drag and moment is predicted underdynamic stall conditions. The research manifests that the SBRF reduced-ordermodeling approach is ideally suited for a variety of aeroelastics and active/passivedesign optimization studies that require high fidelity aerodynamic response solutionswith efficiency as high as that of semi-empirical models.6) The flow field around static and pitching airfoil is simulated with synthetic jet as anactive flow control method. The study shows that: for static airfoil, under attachedflow with small angle of attack, jet actuation has a negative impact on the airfoilperformance; in prestall regime, the jet enhances the airfoil performance remarkably;and in the poststall regime, the effect diminishes and becomes weak. For pitchingairfoil, the synthetic jet can effectively suppress the hysteresis for a large portion ofthe oscillation cycle. However, for a limited range with large angle of attack in deepstall, strong vortex shedding and aerodynamic oscillation still exist.更多还原