风力机异步变桨的初步研究

针对当前同步变桨距式风力机的变桨特点,总结同步变桨距式风力机缺点,提出要使叶片始终处于最佳升阻比状态必须实现风力机的异步变桨这一观点。通过对风力机组工作状态的理论分析,得出实现这一目标变桨系统所应达到的要求。     

风力机最佳攻角与最大升阻比攻角非等同性研究

为提高风力机风能利用率,追求最大风能利用系数,对水平轴风力机最佳攻角与最大升阻比攻角的非等同性进行了理论分析,并采用叶素动量理论对其进行实例论证,以及通过计算流体力学(CFD)对结论进行仿真验证。研究结果表明,二者具有非等同性,最佳攻角略大于最大升阻比攻角,处于最佳工作点的风力机具有更高的风能利用系数,同时具有最大的速度比阈值区间。研究进一步发现,对于目前工作于最大升阻比攻角状态的风力机,通过减小叶尖速比的方式可以使其过渡到最佳攻角状态。     

叶片出气边开槽V结构对水平轴风力机翼型气动性能的影响

为探究具有鸮类特征的风力机叶片出气边开槽的V结构表面气动性能,采用SST k-ω湍流模型,对750 W的标准风力机叶片和仿生风力机叶片翼型的周围流场进行计算。结果表明:仿生V结构表面的风力机叶片阻力系数和吸力面的压力系数均小于标准叶片。分析发现V结构表面能够改变旋涡区位置,漩涡区偏离叶片表面,流动阻力减小。在测量攻角(α=0°～30°)范围内,标准叶片和仿生叶片的升阻比都呈现先递增后减小的规律。在攻角为20°时,标准叶片的升阻比达到最大值,其值为4.03。攻角为25°时仿生V结构风力机叶片的升阻比达到最大值,相比于标准叶片,升阻比增加了73.7%,压力面附着效应增强,升阻比得到提高。     

100 W风力机叶片仿生设计与试验研究

通过数值模拟,分析家燕翼型气动性能;采用家燕翼型,改进100 W水平轴风力机叶片;进行仿家燕翼型叶片气动性能分析;搭建小型水平轴风力机测试平台,完成仿家燕翼型风力机与标准风力机效率对比试验。结果表明:家燕翼型气动特性优良,最大升力系数是标准翼型的1.78倍,最大升阻比是标准翼型的1.77倍;仿家燕翼型叶片输出功率高于标准叶片,平均提高26.48%。     

风力机叶片高升力系数法的气动设计研究

在动量-叶素理论和Betz理论的基础上,结合PROPID软件进行功率为1.5 MW水平轴风力机叶片的气动设计研究。叶片气动设计采用高升力系数法,叶片剖面采用NPU-WA系列高升力、高升阻比风力机专用翼型,在叶片性能预测中采用叶尖损失、轮毂损失和Viterna失速模型。设计结果表明采用先进风力机翼型并运用高升力系数法设计的大功率风力机叶片的弦长较小,叶片面积较小,有利于减轻叶片的重量,同时降低制造成本。     

基于元胞遗传算法的风力机叶片优化设计

采用经过叶尖损失、轮毂损失及失速状态下动量理论修正的片条理论为基础,在满足设计功率的前提下,以最大升阻比系数为优化目标,以叶片的形状参数弦长、扭角为优化设计变量,通过元胞自动机遗传算法对风力机叶片进行优化。最后应用该优化模型对某2 MW变桨距风力机叶片进行优化设计,并对优化结果进行比较分析,验证了该算法的有效性,为风力机叶片的后续研究奠定了基础。     

水平轴风力机叶片扭角和弦长的理想分布

为得到风力机功率、转矩和推力等性能随尖速比和翼型升阻比变化的极限公式,需求解叶片的理想扭角和弦长沿翼展变化的解析表达式,同时这项研究也可为叶片外形设计提供理论参考。为此首先从效率最大化的原则出发,用极值的微分算法证明最佳攻角就是使翼型升阻比最大的攻角;其次利用最佳攻角和入流角公式推导出叶片理想扭角沿展向的解析表达式;然后根据动量-叶素理论,推导出叶片理想弦长沿展向的解析表达式。研究表明:叶片理想扭角是设计尖速比、最佳攻角和风轮半径的函数,叶片理想弦长是设计尖速比、风轮半径以及对应最佳攻角的升力和阻力系数的函数。这两个表达式均可表示为显函数的形式。     

涡流发生器对风力机翼型气动特性的影响研究

涡流发生器作为一种有效的流动控制方法之一,已被成功应用于改善风电叶片的气动特性,众多研究表明,涡流发生器的使用可以有效延迟气流分离,提高升阻比。为了深入了解加装涡流发生器的增升减阻特性,本文以NACA63-415翼型为研究对象,通过数值模拟方法研究分析了不同形状、不同弦向安装位置和多个攻角下涡流发生器对风力机叶片气动特性的影响,结果表明:在不同形状、不同安装位置及攻角下涡流发生器均可有效抑制风力机叶片边界层分离、提高升阻比,其中20%翼型弦向处安装的涡流发生器增升减阻效果最好。     

尾缘厚度对风力机翼型气动特性影响参数化研究

该文拟从气动性能角度考察钝尾缘厚度对风力机翼型气动特性的影响.采用美国NREL带有试验数据的风力机专用翼型S814和S827,通过XFOIL软件对翼型尾缘厚度参数化处理.在最大厚度、弯度和弦宽不变的条件下,尾缘厚度相对于弦长在0.5%～5.0%范围变化.数值计算分析认为,尾缘厚度在一定范围增大时,翼型升力系数有明显提升,同时阻力系数也持续增大,升阻比则呈先增后降趋势,研究翼型尾缘厚度在1.5%(相对弦长)附近其升力系数和升阻比同时达到最佳.研究结论可供风力机叶片设计时量化参考.     

水平轴风力机叶片翼型流场的数值模拟

为了直观形象地探讨水平轴风力机叶片翼型的气动特性,利用计算流体力学软件FLUENT对水平轴风力机叶片常用翼型NACA63425流场进行了数值模拟,得出了翼型NA-CA63425在不同来流攻角下的升力系数、阻力系数、升阻比和不同流攻角下的流场流线图和翼型表面的压力分布。根据模拟结果对不同攻角下尾迹漩涡分离流动进行了分析和比较,得出该翼型气动特性随攻角的变化规律。     

表面粗糙度对风力机翼型性能的影响

讨论了风力机专用叶片上局部增加表面粗糙度，在不同分布位置、不同当量大小的条件下对叶片气动性能影响的实验研究。首先，探讨了叶型表面粗糙度的形成机理和对气动性能影响的初步原理。其次，设计了在风洞实现局部增加表面粗糙度对翼型性能影响的实验条件和实验方案。最后，对风力机专用叶型进行的叶片表面局部增加粗糙度的风洞实验，结果证明了在叶片压力面尾缘通过适当增加一定宽度、一定粗糙度的粗糙带可以增大叶片的有效升力系数。     

Performances of ideal wind turbine

If there is an ideal wind turbine, its performances will be the pursuit goals for designing the actual wind turbine. In this paper, the wind turbine that has the maximum efficiency is defined as ideal wind turbine, which has three main features: lift-drag ratio is infinite, it has enough number blades so that the blade tip and root losses can be ignored, and its blades are limited in width. Using blade element theory, the differential equations of power, torque, lift and thrust of blade element were derived, and the expressions of power, torque, lift and thrust coefficients of the ideal wind turbine were gained by integrating along the blade span. Research shows that the power, torque and lift coefficients of the ideal wind turbine are functions of tip-speed ratio. When the lift-drag ratio and the tip-speed ratio is approaching infinity, power coefficient of the ideal wind turbine is close to the Betz limit; The torque limit is 0.401 when the tip-speed ratio equals about 0.635; The Lift limit is 0.578 when the tip-speed ratio equals about 0.714; The thrust coefficient is 8/9, which is unrelated with tip-speed ratio. For any wind turbine which tip-speed ratio is less than 10, the power coefficient is unlikely to exceed 0.585, for any high-speed wind turbine which tip-speed ratio is greater than 6, the torque coefficient in steady state is unlikely to exceed 0.1, and the lift coefficient is unlikely to exceed 0.2.     

尾缘襟翼对风力机翼型气动特性影响研究

尾缘襟翼(TEF)因其对翼型气动特性的调控能力,被认为是降低叶片疲劳和局部载荷最具可行性的气动控制部件。对TEF进行建模,采用Xfoil和CFD软件分析了TEF对翼型气动特性的影响及其机理,并从叶素理论角度对变化来流下TEF的减载效果进行了验证,结果表明:TEF位于不同摆角时翼型升阻力系数均有不同程度的变化,TEF可有效实现对翼型气动特性的主动控制;TEF摆动改变了翼型表面的静压分布和流动状态,进而对翼型升阻力和失速攻角产生影响;TEF可快速有效降低风速突然增加后的叶素受力,进而控制并减小叶片载荷。     

Magnus type wind turbines: Prospectus and challenges in design and modelling

One of attracting concepts has been the use of Magnus effect to produce lift from rotating cylinders in various engineering applications. With emerging innovative Magnus type wind turbine technology, it is important to determine power performance and characteristics of such generators as correctly as possible. As stressed by Seifert, there is lack of theories in design and modelling of using Magnus force in engineering which is particularly noticed for the horizontal axis Magnus type wind turbines. In this study, the importance of research carried out for determining lift and drag forces of rotating circular cylinders is highlighted and reviewed. Then, the theoretical methods used in designing commercial aerofoil type wind turbines are extended to apply on the Magnus types. New formulation is presented for potential flow around the Magnus blades. The blade element momentum (BEM) theory is formulated for the Magnus wind turbines. A cubic function for angular induction factor is found from the BEM analysis which is strongly dependant on the drag to lift ratio. It is also observed that the relative wind incidence angle and the local power coefficient of the Magnus cylinder are independent functions of spin ratio.     

Aero-elastic behavior of a flexible blade for wind turbine application: A 2D computational study

This paper presents a computational study into the static aeroelastic response of a 2D wind turbine airfoil under varying wind conditions. An efficient and accurate code that couples the X-Foil software for computation of airfoil aerodynamics and the MATLAB PDE toolbox for computation of the airfoil deformation is developed for the aero-elastic computations. The code is validated qualitatively against computational results in literature. The impact of a flexibility of the airfoil is studied for a range of design parameters including the free stream velocity, pitch angle, airfoil thickness, and airfoil camber. Static aero-elastic effects have the potential to improve lift and the lift over drag ratio at off-design wind speed conditions. Flexibility delays stall to a large pitch angle, increasing the operating range of a flexible blade airfoil. With increased thickness the airfoil deformation decrease only linearly.     

分形尾缘叶片气动性能及流场数值模拟

针对风力机存在尾流效应问题,通过在垂直轴风力机叶片尾缘布置分形孔的方法,建立分形叶片三维实体造型,进行了分形叶片和原始叶片三维非定常不可压流动的分析,得出叶片绕流流场数值模拟结果,重点研究具有分形特征的尾缘对叶片尾流流场及叶片气动特性的影响。结果表明:分形叶片对改善叶片尾流流场有较显著作用。在8°~18°攻角范围内,分形叶片升、阻力系数随攻角变化波动性小于原始叶片;当攻角大于原始叶片失速攻角时,这种波动性差距更大。分形孔的存在使叶片周围流场结构及气动参数对攻角变化敏感性降低:在攻角大于原始叶片失速攻角时,分形叶片阻力系数随攻角变化标准差仅为原始叶片的0.6倍,升力系数标准差仅为原始叶片0.4倍。研究结果将改善垂直轴风力机叶片尾流互相干扰及水平轴风力机叶尖脱落涡情况。     

外部环境对风电机组性能影响分析

以1.5 MW风电机组叶片为模型,通过叶片数据采集和实验分析的方法,对外部环境对风电机组性能影响进行分析。通过Bladed软件对风电机组叶片进行仿真,研究结果表明:温度和高度的变化对空气密度和空气黏度的变化有一定影响,空气密度的变化引起升阻比变化,空气黏度的变化则主要引起雷诺数的变化,两者共同对风电机组的气动性产生影响。该研究有助于风电机组的设计研发,降低风电机组运行时的故障率。     

Blade sections for wind turbine and tidal current turbine applications–current status and future challenges

The designers of horizontal axis wind turbines and tidal current turbines are increasingly focusing their attention on the design of blade sections appropriate for specific applications. In modern large wind turbines, the blade tip is designed using a thin airfoil for high lift : drag ratio, and the root region is designed using a thick version of the same airfoil for structural support. A high lift to drag ratio is a generally accepted requirement; however, although a reduction in the drag coefficient directly contributes to a higher aerodynamic efficiency, an increase in the lift coefficient does not have a significant contribution to the torque, as it is only a small component of lift that increases the tangential force while the larger component increases the thrust, necessitating an optimization. An airfoil with a curvature close to the leading edge that contributes more to the rotation will be a good choice; however, it is still a challenge to design such an airfoil. The design of special purpose airfoils started with LS and SERI airfoils, which are followed by many series of airfoils, including the new CAS airfoils. After nearly two decades of extensive research, a number of airfoils are available; however, majority of them are thick airfoils as the strength is still a major concern. Many of these still show deterioration in performance with leading edge contamination. Similarly, a change in the freestream turbulence level affects the performance of the blade. A number of active and passive flow control devices have been proposed and tested to improve the performance of blades/turbines. The structural requirements for tidal current turbines tend to lead to thicker sections, particularly near the root, which will cause a higher drag coefficient. A bigger challenge in the design of blades for these turbines is to avoid cavitation (which also leads to thicker sections) and still obtain an acceptably high lift coefficient. Another challenge for the designers is to design blades that give consistent output at varying flow conditions with a simple control system. The performance of a rotating blade may be significantly different from a non‐rotating blade, which requires that the design process should continue till the blade is tested under different operating conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

风力发电机叶片设计与气动性能仿真研究

运用叶素理论和气动理论,基于设定的风力机性能参数对风轮叶片进行三维设计。利用Gambit建模软件对风力机单叶片进行三维建模,再用Fluent软件进行风力机叶片气动性能的数值模拟,仿真叶片气动流场流态,并计算叶轮的升力、阻力和扭转力矩;验证风力机气动性能数值模拟的可行性和可靠性;计算发电机组功率和风能利用效率等性能参数。对风力发电机叶片的设计和气动数值模拟计算分析的工作可深化对风力发电机组三维叶片的气动性能的了解,仿真风力发电机组气动流场,能为风力机叶片的设计、改型和研发工作提供技术参数和指导意见。