垂直轴风力机两种翼型气动性能比较研究

叶片是风力机最重要的组成部分,在不同的风能资源情况下,翼型的选择对垂直轴风力机气动特性有着重要的影响。文章分别以NACA0018翼型(对称翼型)和NACA4418翼型(非对称翼型)建立3叶片H型垂直轴风力机二维仿真模型。应用数值模拟的研究方法,从功率系数、单个叶片切向力系数等方面比较两种风力机模型在不同叶尖速比下的气动特性,并采用风洞实验数据验证了流场计算的准确性。CFD计算结果表明:在低叶尖速比下,NACA4418翼型风力机气动特性优于NACA0018翼型风力机,适用于低风速区域;在高叶尖速比下,NACA0018翼型风力机气动特性较好,适用于高风速地区。而且在高叶尖速比时,NACA0018翼型在上风区时,切向力系数平均值要高于NACA4418翼型,在下风区时,NACA418翼型切向力系数平均值高。该研究可为小型垂直轴风力机翼型的选择提供参考。     

Wells turbine blade profile optimization for better wave energy capture

Despite the fact that wave energy is available at no cost, it is always desired to harvest the maximum possible amount of this energy. The axial flow air turbines are commonly used with oscillating water column devices as a power take‐off system. The present work introduces a blade profile optimization technique that improves the air turbine performance while considering the complex 3D flow phenomena. This technique produces non‐standard blade profiles from the coordinates of the standard ones. It implements a multi‐objective optimization algorithm in order to define the optimum blade profile. The proposed optimization technique was successfully applied to a biplane Wells turbine in the present work. It produced an optimum blade profile that improves the turbine torque by up to 9.3%, reduces the turbine damping coefficient by 10%, and increases the turbine operating range by 5%. The optimized profile increases the annual average turbine power by up to 3.6% under typical sea conditions. Moreover, new blade profiles were produced from the wind turbine airfoil data and investigated for use with the biplane Wells turbine. The present work showed that two of these profiles could be used with low wave energy seas. Copyright © 2017 John Wiley & Sons, Ltd.     

Multi-objective optimization of the airfoil shape of Wells turbine used for wave energy conversion

Wells turbine is one of the technical systems allowing an efficient use of the power contained in oceans’ and seas’ waves with a relatively low investment level. It converts the pneumatic power of the air stream induced by an Oscillating Water Column into mechanical energy. The standard Wells turbines show several well-known disadvantages: low tangential force, leading to low power output from the turbine; high undesired axial force; usually a low aerodynamic efficiency and a limited range of operation due to stall. In the present work an optimization process is employed in order to increase the tangential force induced by a monoplane Wells turbine using symmetric airfoil blades. The automatic optimization procedure is carried out by coupling an in-house optimization library (OPAL (OPtimization ALgorithms)) with an industrial CFD (Computational Fluid Dynamics) code (ANSYS-Fluent). This multi-objective optimization relying on Evolutionary Algorithms takes into account both tangential force coefficient and turbine efficiency. Detailed comparisons are finally presented between the optimal design and the classical Wells turbine using symmetric airfoils, demonstrating the superiority of the proposed solution. The optimization of the airfoil shape leads to a considerably increased power output (average relative gain of +11.3%) and simultaneously to an increase of efficiency (+1%) throughout the full operating range.     

潮流能水轮机叶片翼型水动力性能的数值模拟研究

鉴于潮流能水轮机叶轮叶片性能的好坏关系到叶轮的捕能效果,而叶片翼型的水动力性能是叶片设计的基础,基于CFD软件ANSYS CFX对部分翼型的水动力性能进行了分析。首先在不同湍流模型下对NACA2412翼型的部分水动力特性进行数值模拟并与试验值做对比分析;然后在SST湍流模型下,对NACA64421翼型在攻角为0°时,探讨了边界层网格对数值模拟结果的影响;并对其在攻角为-2°~20°情形下的水动力性能进行了数值模拟。结果表明,湍流模型的选用、边界层网格划分及近壁尺寸的选取对数值模拟结果的影响均较大,并通过数值模拟得到了NACA64421翼型的升力系数、阻力系数、最佳攻角、失速角等水动力性能参数,可为水轮机叶片设计时翼型的选取提供参考。     

振荡水柱波浪发电空气透平工作特性数值模拟

为更深入地探讨振荡水柱式波能发电装置的原理,对用于波力发电装置二次能量转换的威尔斯式透平进行了三维全流道模拟计算。针对对称翼型叶片和非对称翼型叶片的威尔斯式透平,分别考察了其在不同叶片安装角下的效率和出力随流量系数的变化趋势,得出了不同叶片安装角时威尔斯式透平运行的最佳参数。在相同工况下,对比分析了不同翼型叶片威尔斯式透平的效率、出力、输入系数及扭矩系数随流量系数的变化,并比较了叶片表面的压力分布情况。结果表明,随着叶片安装角增大,装置最高效率值增大,且在安装角大于9°后变化缓慢,而装置最大出力却随着安装角的增大而减小;采用非对称翼型叶片时,装置的出力、输入系数、扭矩系数均大于相同工况下对称翼型叶片装置。     

Effect of guide vanes on the performance of a self-rectifying air turbine with constant and variable chord rotors

A Wells turbine is a self-rectifying air flow turbine capable of converting pneumatic power of the periodically reversing air stream in Oscillating Water Column into mechanical energy. The Wells turbine has inherent disadvantages; lower efficiency, poorer starting characteristics, higher axial force and low tangential force in comparison with conventional turbines. Guide vanes before and after the rotor suggest a means to improve the tangential force, hence its efficiency. Experimental investigations are carried out on a Wells turbine with the constant chord and variable chord blade rotors fitted with inlet and outlet guide vanes to understand the aerodynamics. Experiments were also conducted for the above said rotors with various stagger angles to validate the design stagger angle. In addition, the starting and running characteristics of the rotors have been studied and compared with the case without guide vanes. Studies were done at various flow coefficients covering the entire range of flow coefficients over which the turbine is operable. The efficiency, starting characteristics of the turbines with guide vanes have improved when compared with the respective turbines without guide vanes.     

新型变桨立轴风力机涡效应分析

该文旨在通过变桨来改善升力型立轴风力机叶片气动特性,提高风力机最大运行效率。针对设计尖速比下风能利用系数较低的问题,提出减小叶片小攻角范围,增大叶片大攻角工作范围,以重点改善叶片低性能区域的气动特性为出发点,提高风能利用系数新变桨思路。以采用NACA0012翼型、2 m高和2 m旋转直径的两叶片H型风力机为研究对象,从涡理论来分析和比较在最佳尖速比为5的条件下,附着涡、尾随涡、脱体涡和桨距角对攻角、切向力和功率输出的影响规律。研究结果表明:变桨后,叶片的攻角、切向力和输出功率在原最大值两侧均有明显提高,拓宽了叶片高性能的工作区域;涡系中脱体涡对叶片气动特性影响最大,其中在上盘面影响较小,在下盘面影响较大;变桨前后涡系对上盘面的差异较小,对下盘面的影响差异较明显;变桨后,下盘面的叶片的涡尾迹弯曲程度在加大。     

基于复合形法的垂直轴风力机翼型优化设计

针对低速航空翼型不完全适合垂直轴风力机的问题,采用复合形法对小型垂直轴风力机常用的NACA0015翼型进行了优化设计。在复合形法优化设计过程中,选取翼型的弯度和厚度作为设计变量,以翼型最大切向力系数Ctmax和失速攻角αs的加权和作为目标函数。将XFOIL程序与Viterna-Corrignan失速后模型相结合,计算出优化前后翼型气动性能参数。结果表明,与NACAOO15翼型相比,新翼型的气动性能有了较大提高,最大升力系数增大了33.5%,失速攻角提高了3°,最大切向力系数增大了43.5%。     

Comparison of Performances of Turbines for Wave Energy Conversion

The Wells turbine for a wave power generator is a self-rectifying air turbine that is available for an energy conversion in an oscillating water-air column without any rectifying valve. The objective of this paper is to compare the performances of the Wells turbines in which the profile of blade are NACA0020, NACA0015, CA9 and HSIM15-262123-1576 in the small-scale model testing. The running characteristics in the steady flow, the start and running characteristics in the sinusoidal flow and the hysteretic characteristics in the sinusoidal flow were investigated for four kinds of turbine. As a conclusion, the turbine in which the profile of blade is NACA0020 has the best performances among 4 turbines for the running and starting characteristics in the small-scale model testing.     

Gurney襟翼对水平轴风力机性能影响的实验研究

在小型低速风洞中对装有NACA4424翼型叶片的水平轴风力机及在其尾缘加装Gurney襟翼的风力机进行了一系列性能对比实验。Gurney襟翼的高度分别为2%b和4%b(b为翼型弦长),叶片安装角在6°~14°范围内,实验风速为6~15m/s。实验结果表明,Gurney襟翼对水平轴风力机性能有显著影响,特别是在大安装角(即大攻角和大升力)下;在小安装角(即小攻角和小升力)时,Gurney襟翼使风力机性能降低。同时,装2%b襟翼的风力机性能要高于装4%b襟翼的风力机;在12°安装角时,前者提高风力机功率最少有39%,而后者也可提高风力机功率在34%以上。对于风力机最常用的叶型FFA-W3-211加装2%b的Gurney襟翼后的风洞对比实验同样证明了上述结论。     

Wave energy harvesting using a novel turbine rotor geometry

Wells turbines provide a practical solution for wave energy harvesting. The low aerodynamic efficiency of Wells turbines tangibly reduces their output power. Both the turbine efficiency and output power depend on the turbine solidity. The turbine solidity decreases from rotor hub to rotor tip for the commonly used rotors with constant chord‐length blades. The present work introduces a novel Wells turbine rotor geometry. This geometry was obtained by numerically optimizing the rotor's radial solidity distribution. The turbine performance with different rotor geometries was numerically simulated by solving the three‐dimensional Reynolds‐averaged Navier–Stocks equation under incompressible and steady state flow conditions. Simple and multi‐objective optimization were implemented in order to obtain the optimum rotor geometry. The present work showed that an improved turbine performance can be achieved by optimizing the turbine radial solidity distribution. Two different optimized rotor geometries were obtained and presented. The first rotor geometry improved the turbine efficiency by up to 4.7% by reducing its pressure drop. The second rotor geometries enhanced the turbine output power by up to 10.8%. Copyright © 2016 John Wiley & Sons, Ltd.     

风力机翼型的气动性能分析

风力机翼型气动性能分析是风力机气动设计和运行优化的重要基础。采用NUMECA软件对弯度为4%的风力机NACA4412翼型进行气动数值模拟,并与实验数据进行比较,取得比较一致的结果。在此基础上,对NACA2412、NACA4412、NACA6412不同弯度的翼型进行模拟分析,对三种翼型在不同攻角下的气动性能进行了比较,为风力机翼型弯度选择和翼型改型设计提供参考意见。     

基于滑移网格的垂直轴潮流水轮机的三维数值模拟

为了探究翼型对垂直轴水轮机水力效率的影响,基于叶素理论分析建立了垂直轴潮流水轮机在水槽中的物理模型,采用滑移网格技术在Fluent软件中对模型的流场进行了三维数值模拟。在保持转速一定、更改来流速度即改变叶尖速比的条件下,分析了两种不同NACA翼型直叶片的潮流水轮机内部流场以及水力性能。结果表明,翼型以及叶片安装角对垂直轴潮流水轮机的利用效率影响很大,其流动特性与来流速度、叶片布置形式有重要联系,为新型潮流水轮机的设计和翼型的选择应用提供了依据。     

Analysis of aerodynamic load on straight-bladed vertical axis wind turbine

This paper presents a wind tunnel experiment for the evaluation of energy performance and aerodynamic forces acting on a small straight-bladed vertical axis wind turbine (VAWT) depending on several values of tip speed ratio. In the present study, the wind turbine is a four-bladed VAWT. The test airfoil of blade is symmetry airfoil (NACA0021) with 32 pressure ports used for the pressure measurements on blade surface. Based on the pressure distributions which are acted on the surface of rotor blade measured during rotation by multiport pressure-scanner mounted on a hub, the power, tangential force, lift and drag coefficients which are obtained by pressure distribution are discussed as a function of azimuthally position. And then, the loads which are applied to the entire wind turbine are compared with the experiment data of pressure distribution. As a result, it is clarified that aerodynamic forces take maximum value when the blade is moving to upstream side, and become small and smooth at downstream side. The power and torque coefficients which are based on the pressure distribution are larger than that by torque meter.     

Numerical investigation on the effect of blade sweep on the performance of Wells turbine

A Wells turbine is one of the simplest and promising self-rectifying air turbines which is basic to the needs of the near future and likely to be economically viable. With the recent development in computer hardware and software, it has now become practicable to conduct a reasonable computation of three-dimensional turbulent flows through complex geometry. To investigate the effect of blade sweep on the performance of the Wells turbine, the numerical investigation was carried out under steady flow condition with a fully 3-D Navier–Stokes code for two kinds of blades, NACA0020 and CA9. As a result, it was found that the performance of the Wells turbine is considerably influenced by the blade sweep. The optimum blade sweep ratio (f=0.35) for the NACA0020 was found. This value is just the same as one obtained experimentally by the authors in the past. It was also found that the overall turbine performance for the NACA0020 is better than that for the CA9. It was shown that the numerical method is able quite well to predict the effect of blade sweep of the Wells turbine. The detailed flow patterns for several blade sweeps were also shown and discussed in this paper.     

The Darrieus wind turbine: Proposal for a new performance prediction model based on CFD

This paper presents a CFD model for the evaluation of energy performance and aerodynamic forces acting on a straight-bladed vertical-axis Darrieus wind turbine. The basic principles which are currently applied to BE-M theory for rotor performance prediction are transferred to the CFD code, allowing the correlation between flow geometric characteristics (such as blade angles of attack) and dynamic quantities (such as rotor torque and blade tangential and normal forces). The model is proposed as a powerful design and optimization tool for the development of new rotor architectures for which test data is not available.After describing and validating the computational model against experimental data, a full campaign of simulation is proposed for a classical NACA 0021 three-bladed rotor.Flow field characteristics are investigated for several values of tip speed ratio, allowing a comparison among rotor operation at optimum and lower C_p values, so that a better understanding of vertical-axis wind turbines basic physics is obtained.     

Aerodynamic shape optimization of wind turbine blades using a Reynolds‐averaged Navier–Stokes model and an adjoint method

Computational fluid dynamics (CFD) is increasingly used to analyze wind turbines, and the next logical step is to develop CFD‐based optimization to enable further gains in performance and reduce model uncertainties. We present an aerodynamic shape optimization framework consisting of a Reynolds‐averaged Navier Stokes solver coupled to a numerical optimization algorithm, a geometry modeler, and a mesh perturbation algorithm. To efficiently handle the large number of design variables, we use a gradient‐based optimization technique together with an adjoint method for computing the gradients of the torque coefficient with respect to the design variables. To demonstrate the effectiveness of the proposed approach, we maximize the torque of the NREL VI wind turbine blade with respect to pitch, twist, and airfoil shape design variables while constraining the blade thickness. We present a series of optimization cases with increasing number of variables, both for a single wind speed and for multiple wind speeds. For the optimization at a single wind speed performed with respect to all the design variables (1 pitch, 11 twist, and 240 airfoil shape variables), the torque coefficient increased by 22.4% relative to the NREL VI design. For the multiple‐speed optimization, the torque increased by an average of 22.1%. Depending on the CFD mesh size and number of design variables, the optimization time ranges from 2 to 24h when using 256 cores, which means that wind turbine designers can use this process routinely. Copyright © 2016 John Wiley & Sons, Ltd.     

The performance of Wells turbine under bi-directional airflow

This paper presents the performance of a Wells turbine operating under unsteady bi-directional airflow conditions. In this study, four kinds of blade profile were selected, NACA0020, NACA0015, CA9 and HSIM 15-262123-1576. The experiments have been carried out for two solidities under sinusoidal and irregular unsteady flow conditions based on Irish waves (Site2). It was found that for a Wells turbine operating under bi-directional air flow, the rotor geometry preferred is the blade profile of CA9 with rotor solidity σ=0.64. In addition, the efficiency curve of the Wells turbine under unidirectional flow conditions fails to present the rapid rise in the instantaneous efficiency which occurs at low flow coefficient of bi-directional flow condition. A comparative analysis between the numerical simulation results and experimental results was carried out. As a result, an excellent agreement was found between the numerical and experimental results. In addition, the effect of blade profile and rotor solidity on hysteretic characteristics of the turbine has been clarified experimentally under bi-directional airflow.     

Fluid structure interaction of a morphed wind turbine blade

One serious challenge of energy systems design, wind turbines in particular, is the need to match the system operation to the variable load. This is so because system efficiency drops at off‐design load. One strategy to address this challenge for wind turbine blades and obtain a more consistent efficiency over a wide load range, is varying the blade geometry. Predictable morphing of wind turbine blade in reaction to wind load conditions has been introduced recently. The concept, derived from fish locomotion, also has similarities to spoilers and ailerons, known to reduce flow separation and improve performance using passive changes in blade geometry. In this work, we employ a fully coupled technique on CFD and FEM models to introduce continuous morphing to desired and predetermined blade design geometry, the NACA 4412 profile, which is commonly used in wind turbine applications. Then, we assess the aerodynamic behavior of a morphing wind turbine airfoil using a two‐dimensional computation. The work is focused on assessing aerodynamic forces based on trailing edge deflection, wind speed, and material elasticity, that is, Young's modulus. The computational results suggest that the morphing blade has superior part‐load efficiency over the rigid NACA blade. Copyright © 2013 John Wiley & Sons, Ltd.     

基于CFD技术与遗传算法的风力机大厚度翼型优化设计

针对目前风力机大厚度翼型设计参数空间有限、优化设计过程中气动力预测不准等问题,利用B样条函数表征通用翼型廓线,编制程序集成耦合翼型设计模块、任意翼型自适应网格模块、CFD流场计算模块、遗传算法优化模块,提出了基于CFD技术与遗传算法的风力机叶片大厚度翼型优化设计方法,并对比分析优化新翼型与DU97-W-300翼型的几何特性与气动性能。结果表明,优化方法设计的新翼型在主要攻角范围内具有较高的气动性能,在雷诺数为3.0×106的情况下,其升力系数、升阻比分别提高了13.555%、38.588%。该翼型优化设计方法为风力机大厚度通用翼型的设计与应用提供参考。