Progresses in application of computational fluid dynamic methods to large scale wind turbine aerodynamics

The computational fluid dynamics (CFD) methods are applied to aerodynamic problems for large scale wind turbines. The progresses including the aerodynamic analyses of wind turbine profiles, numerical flow simulation of wind turbine blades, evaluation of aerodynamic performance, and multi-objective blade optimization are discussed. Based on the CFD methods, significant improvements are obtained to predict two/three dimensional aerodynamic characteristics of wind turbine airfoils and blades, and the vortical structure in their wake flows is accurately captured. Combining with a multi-objective genetic algorithm, a 1.5 MW NH-1500 optimized blade is designed with high efficiency in wind energy conversion.     

串列风力机尾流干扰的研究简

广义致动盘方法是通过引入体积力代替叶片的致动盘技术与三维Navier-Stokes 方程相结合来获得风力机周围流场信息的一种方法. 该方法避免了花费大量网格与计算资源去求解风力机叶片的附面层,从而可以把更多的网格与计算资源用于风力机尾流流场的模拟,非常适合用于风力机尾流流场的研究. 以NH1500风力机为计算模型,将常规CFD (computational fluid dynamics) 方法与广义致动盘方法计算所得的叶片载荷分布进行比较,以验证广义致动盘方法的可行性. 然后使用广义致动盘方法对风场中串列风力机进行数值模拟,研究串列风力机之间间距变化时,上游风力机产生的尾流对下游风力机的干扰影响.     

A Vibration Estimation Method for Wind Turbine Blades

This paper reports the development of a vibration monitoring system for wind turbine blades. This system is used to estimate the deflection at the tip blade on a wind turbine tower. Technical accidents of wind turbine blades have become increasingly common. Thus, regular monitoring of the blades is very important to prevent breakdowns, especially in cases when the blades begin to vibrate excessively. The monitoring system developed in this study satisfies two main objectives for practicality. First, our system is easy to install on existing wind turbines. Second, blade deflection is measured in real time. Our system can be operated using a few strain gages attached at the blade root, and the deflection is calculated based on the monitored stress. Thus, direct measurement of deflection at the blade tip is unnecessary. An estimation algorithm for this purpose is adopted based on the experimental modal analysis. This paper focuses on the evaluation of the estimation algorithm to investigate the feasibility of our system. Basic experiments were conducted using a simple blade model of a 300 W scaled wind turbine under rotation. Signals from the strain gages were acquired by a sensor network and sent to a computer through a wireless connection. The results show that the estimation accuracy is acceptably high. Therefore, we conclude that our proposed system is practical.     

大于切出风速的大型风力机运行控制策略研究

运用非定常叶素动量(BEM)理论计算气动载荷,叠加重力载荷和惯性载荷,建立并数值求解全机动力学模型。基于快速非支配排序遗传算法(NSGA),在切出风速以上,优化得到变速变桨和定速变桨两种控制规律曲线,实现大型风力机在25m/s~40m/s风速之间正常运行的目的。比较两种控制策略的输出功率、风轮推力和转矩,得出变速变桨控制策略更适合于25m/s~40m/s之间风力机运行控制的结论。计算稳态工况时8种叶根载荷的极限值,由各载荷的变化趋势可知,Fy在25m/s之后增大9%,其他载荷均安全。     

Supercritical and subcritical dynamic flow-induced instabilities of a small-scale wind turbine blade placed in uniform flow

There is a growing interest in extracting more power per turbine by increasing the rotor size in offshore wind turbines. As a result, the turbine blades will become longer and therefore more flexible, and a flexible blade is susceptible to flow-induced instabilities. In order to design and build stable large wind turbine blades, the onset of possible flow-induced instabilities should be considered in the design process. Currently, there is a lack of experimental work on flow-induced instabilities of wind turbine blades. In the present study, a series of experiments were conducted and flow-induced instabilities were observed in wind turbine blades. A small-scale flexible blade based on the NREL 5 MW reference wind turbine blade was built using three-dimensional printing technique. The blade was placed in the test section of a wind tunnel and was subjected to uniform oncoming flow, representing the case of a parked wind turbine blade. The blade׳s tip displacement was measured using a non-contacting displacement measurement device as the oncoming wind speed was increased. At a critical wind speed, the blade became unstable and experienced limit cycle oscillations. The amplitude of these oscillations increased with increasing wind speed. Both supercritical and subcritical dynamic instabilities were observed. The instabilities were observed at different angles of attack and for blades both with and without a geometric twist. It was found that the blade twist had a significant influence on the observed instability: a blade without a twist experienced a strong subcritical instability.     

基于CFD技术的垂直轴风力机动态尾流特性研究

利用CFD软件对麦克马斯特大学垂直轴风力机进行不同叶尖速比下的数值模拟,计算结果与风洞试验数据吻合良好。近场尾流中,与单叶片的风力机模拟结果比较,上游叶片产生并向下游延伸的旋涡影响下游运行轨道上叶片的升阻力特性,不仅使叶片扭矩输出峰值降低,而且峰值产生的时间延迟。对垂直轴风力机叶片叶梢进行修改,模拟结果显示,叶片扭矩输出峰值不变,但是谷值有所降低,修改后风力机沿风向推力幅值降低明显;远场尾流中,采用风速轮廓线原理,以瑞典的法尔肯贝里市200kW垂直轴风力机为原型,按照真实的空间排布进行数值模拟。模拟结果显示,上游风力机上下两端处产生较为集中的远场尾流,影响下游风力机叶片下半段的气动性能,下游风力机功率输出降低明显。     

Wake impacts on aerodynamic and aeroelastic behaviors of a horizontal axis wind turbine blade for sheared and turbulent flow conditions

The magnitude and temporal variations of wind speed considerably influence aerodynamic and structural responses of MW-sized horizontal axis wind turbines. Thus, this paper investigates the variations in airloads and blade behavior of a wind turbine blade resulting from operations in sheared and turbulent flow conditions. First, in order to validate the present methods, comparisons of aerodynamic results were made among the blade element momentum method, free-wake method, and numerical results from the previous studies. Then, the validated methods were applied to a national renewable energy laboratory 5 MW reference wind turbine model for fluid–structure interaction analyses. From the numerical simulations, it can be clearly seen that unfavorable airloads and blade deformations occur due to the sheared and turbulent flow conditions. In addition, it is clear that wake impacts are not as substantial at those of high wind speeds; however, the effects obviously affect the aerodynamic and structural behaviors of the blade at lower wind speeds. Therefore, it is concluded that the numerical results markedly indicate the demand for accurate assessment of wake dynamics for accurate estimations of the aerodynamic and structural responses for sheared and turbulent flow environments.     

漂浮运动对风力机气动特性的影响分析

海上浮式风机为蕴藏丰富的深海风能开发提供了有效的解决方案,浮式基础存在的大幅度纵荡、纵摇和艏摇运动可以改变风轮与流场间的相互作用,从而影响风力机的气动特性。基于叶素-动量理论及其修正方法,以NREL 5MW风力机为研究对象,考虑浮式基础运动对叶片不同径向位置处相对入流风速的影响,提出了风载荷的计算模型,通过编程计算获得了叶轮转矩和风力机功率,并比较了不同运动形式对风力机功率波动的影响。结果表明,纵摇对其功率特性影响最大,这为海上浮式风机的优化设计提供理论依据与数据基础。     

Rain erosion of wind turbine blades: computational analysis of parameters controlling the surface degradation

Meccanica - Parameters influencing the erosion behavior of the leading edges of wind turbine blade tips are investigated. Recent enhancements in structural sizes of wind turbines operating at...     

Aeroelastic analysis of wind turbines using a tightly coupled CFD–CSD method

This paper presents aeroelastic analyses of wind turbines, using the compressible flow Helicopter Multi-Block (HMB2) solver of Liverpool University, coupled with a Computational Structural Dynamics method. For this study, the MEXICO and NREL Phase VI wind turbines were employed. A static aeroelastic method was first employed for the analysis of the MEXICO blade and the effect of the torsional stiffness was studied at 10, 15 and 24 m/s axial wind speeds. The torsional deformations showed strong dependency on this parameter and the blade region from mid-span to the tip was the most susceptible to aeroelastic effects. The work progressed by studying both the static and dynamic response on the NREL wind turbine, where the nacelle and the tower were considered. Mean deflections between the static and dynamic methods showed consistency and, due to the structural properties of this blade, flapping modes were dominant. The dynamic aeroelastic method enabled an assessment of the effect of flapping on the blade loads, in conjunction with the effect of tower. Aeroelastic effects were found to be secondary for the MEXICO blade, but had a stronger effect on the larger NREL Phase VI blade.