不同串列布置间距下2 MW风力机尾流的研究

为合理利用有限的土地资源,提高整个风电场的发电效率,采用FLUENT软件对在不同串列布置间距下的风力机尾流的相互影响情况进行了仿真研究。结果表明:随着风轮间距的增加,下游风轮风速逐渐增大并向着来流风速值靠近,功率损失逐渐减小,上游风轮的尾流对下游风轮产生的扰动作用逐渐减弱;但是风轮间距为10D时,下游风轮已基本摆脱了上游风轮的强尾流区,此后尾流速度变化缓慢。因此,在风电场布局时应合理选择风力机间距。     

风力机垂直交错对下游风力机性能的影响研究

为降低上游风力机尾流的影响、优化风场布置,在两台串联的NERL 5 MW水平轴风力机中间安装1台小型的垂直轴风力机,形成垂直交错风场。采用FLUENT软件对串联风场和垂直交错风场进行数值模拟,对比两种风场的输出功率与流动特性。同时,改变垂直轴风力机的安装位置,分析其与下游风力机的距离对垂直交错风场的影响。结果表明：当风力机串联布置且为标准间距7D(D为风轮直径)时,下游风力机受上游风力机尾流影响仍然很大,输出功率下降57.1%;串联风场中加入垂直轴风力机加快了相应垂直交错风场尾流的恢复,提高了下游风力机的输出功率;垂直交错风场中垂直轴风力机安装距离为1D～6D时,可以在上游风力机功率变化不明显的情况下提高下游风力机的输出功率;当安装距离为6D时,下游风力机提高功率最高,比串联风场增加了40.1%。     

大气湍流稳定度对风力机尾流影响的模拟研究

利用Agel-TDM风力机动力模型,模拟分析不同湍流状态下单台风力机尾流的空间特征。研究结果表明:随着大气湍流稳定性增强,在水平方向上风力机尾流效应减弱,即风力机尾流距离减小;在铅垂方向,动量垂直输送加快,增强了风力机下游风速的恢复速率,风电场的实际出力能力提高。     

基于Park-Gauss模型的风场尾流数值模拟

基于Park模型尾流区线性膨胀假设和径向风速呈高斯分布假设,提出一种新型工程尾流模型Park-Gauss模型,对单台风力机尾流场进行数值模拟研究。采用两种初始尾流半径(风轮半径和紧靠风轮下游处的尾流半径),分别对Park模型、2D Jensen模型以及Park-Gauss模型进行对比研究。经过与风场实测数据和风洞试验的比较,结果表明:以紧靠风轮下游处的尾流半径作为初始尾流半径会明显提高尾流场的预测精度;新提出的ParkGauss模型计算精度优于2D Jensen模型和Park模型;Park-Gauss模型可很好模拟尾流区的风速,不仅在精度上与试验结果接近,而且在径向分布上也更符合真实流场。     

叶片旋向对风力机尾流特性影响的试验研究

采用一种简单、有效的方法来改善风力机尾流效应,提升下游风力机功率。进行叶片旋向对风力机尾流特性的试验研究,利用低频粒子图像测速（PIV）系统对NACA4415翼型的叶片进行扰流流场测试并采集风力机的尾流数据。当2台串列排布的风力机旋向不同时,首先在下游风力机前1D(D为风轮直径)处,叶尖涡涡核位置向中央尾迹区偏移,而外部主流区的流体在叶尖涡诱导区的输运和卷吸作用下持续进入中央尾迹区并与之掺混使得轴向速度恢复得更佳;进而分析下游风力机后1D的流场数据,结果显示：虽然下游风力机叶尖涡几何结构被“打碎”,但涡核能量却未降低;最后探讨影响风力机功率特性的因素,下游风力机入流角的增大促使下游风力机捕获更多风能,在风轮间距为2D时,逆向旋转的功率比比同向旋转时高4.70%,且功率比随间距增加其增幅逐渐减小。     

基于改进的Jensen模型尾流数值模拟研究

为提高垂直方向尾流速度的预测精度，基于尾流速度在垂直方向呈现多项式分布的假设，考虑不同高度自然风速对尾流速度的影响，提出一种改进的Jensen尾流模型。以单台风力机作为研究对象，采用Jensen模型、高斯模型和改进的Jensen模型分别对风力机尾流速度进行数值模拟，并基于改进的Jensen模型分析大气稳定性对尾流速度恢复的影响。仿真结果表明，改进的尾流模型精度优于Jensen模型和高斯模型，在下游2.5D、4.0D和8.0D(D为风轮直径)距离处的误差低至7.35%、2.82%和3.44%。尾流速度恢复和大气稳定性密切相关，越稳定的大气层湍流强度越小，越不利于尾流速度恢复。     

水平轴风力机尾流特性的数值研究

对600kW单风轮和7倍风轮直径(7D)间距的两风轮水平轴风力机在不同来流风速条件进行三维流场数值模拟.结果显示:风力机下游流场存在三维速度流动,轴向速度在尾迹区存在明显亏损,且随尾迹向下游的发展,轴向速度亏损逐渐减少.不同来流风速条件下风轮尾迹流的发展有一定区别,在来流风速较低的条件下尾流风速恢复较快.风场在布置风力机时应考虑当地的风速条件,若多数情况在额定风速或超过额定风速工况下运行,则前后风轮间距应大于7倍风轮直径;否则可考虑缩短前后风轮间距.     

偏航流动对水平轴风力机声辐射影响研究

风力机处于复杂多变的自然风条件下,经常处于偏航状态。文章运用分离涡方法(DES)寻找偏航流动对水平轴风力机声辐射的影响。结果表明:随偏航角度的增加,风轮输出功率减小;垂直风轮旋转面和平行来流方向的测试线上,总声压级都随着远离风轮旋转面逐渐衰减,且随着偏航角的增大,平行来流方向测试线上的声压级降低较快;在不偏航流动下平行于风轮旋转面的声压级,沿旋转方向基本相同,在偏航流动下,随偏航角度的增大而降低;平行于入口面上距离声源面近的一侧声压级较大,且随偏航角的增加逐渐升高;叶尖处声压级最大,中心轴上最小。DES方法用于风力机声辐射的模拟研究是可行的,对风力机气动噪声研究具有一定的参考价值。     

风剪切来流下风力机流场特性与风轮气动载荷研究

以某33 kW两叶片水平轴风力机的风轮为研究对象,采用CFD方法,研究风剪切来流下水平轴风力机流场特性与风轮气动载荷的分布规律。结果表明:在剪切来流下,风轮上游来流风速随方位角的波动曲线偏离由理论计算得到的风速波动曲线;尾流区轴向速度呈现非对称性分布,轮毂上方叶尖涡和叶根涡的移动速度大于轮毂下方叶尖涡和叶根涡的移动速度;同时,风力机叶片和风轮的气动载荷随方位角呈现正余弦的变化趋势,风轮气动载荷功率谱曲线的峰值对应的频率与叶片通过频率的整数倍相关。当风剪切指数由0.1增大到0.5时,风轮转矩和推力的均方根分别减小2.28%和1.43%,但其波动幅值随风剪切指数的增大而增大,并且风轮转矩和推力随方位角的波动曲线存在相位偏移现象,风剪切指数越大,相位偏移现象越明显;风轮偏航力矩和倾覆力矩的均方根分别增大4.07倍和4.04倍,且其波动幅值随风剪切指数的增大而增大。     

NREL 5 MW风力机气动特性的数值模拟研究

以NREL 5 MW风力机为研究对象,忽略风轮的仰角和锥角,采用CFD数值模拟方法并选用SST湍流模型研究均匀来流条件下不同风速时风力机的输出功率,并与FAST软件的计算结果进行比较。分析叶片展向不同截面的压力分布和径向速度流场,讨论风力机尾流场速度和湍动能的变化规律。研究结果表明,沿着叶片展向自叶根至叶尖,吸力面压力逐渐降低,低压区覆盖面积逐渐增大;压力面压力逐渐升高,前缘与尾缘附近压力增幅较大。风穿过风轮能量被大量吸收,风轮对来流的阻塞作用主要集中在近尾流区。风轮后随着流体从近尾流区运动到远尾流区湍动能逐渐减小。     

垂直轴风力机气动特性与涡脱落模态分析

垂直轴风力机运行过程中,叶片上下表面边界层与剪切层的相互作用使风力机下游尾迹形成周期性涡结构,这种尾迹涡结构对风力机空气动力学特性具有重要影响。基于此,该文采用计算流体力学方法对不同工况下垂直轴风力机尾迹涡结构展开研究,利用快速傅里叶变换与相空间轨迹分析不同尖速比下风力机叶片涡脱落现象和尾迹涡结构,并通过分形维数研究转矩与尾迹流场速度变化。结果表明：风力机尾迹涡结构随尖速比变化呈现不同特征,当尖速比为3.6时,风力机尾迹两侧呈规则性反向脱落涡模态;低尖速比垂直轴风力机尾迹具有明显的混沌特性,且随尖速比的增加混沌特性逐渐减弱;随着尖速比的增加,风力机转矩与下游速度分形维数不断降低,且当尖速比为3.6时,风力机下游速度分形维数仅为1.07。     

Wind turbine partial wake merging description and quantification

Individual turbine location within a wind plant defines the flow characterisitcs experienced by a given turbine. Irregular turbine arrays and inflow misalignment can reduce plant efficiency by producing highly asymmetric wakes with enhanced downstream longevity. Changes in wake dynamics as a result of turbine position were quantified in a wind tunnel experiment. Scale model turbines with a rotor diameter of 20 cm and a hub height of 24 cm were placed in symmetric, asymmetric, and rotated configurations. Simultaneous hub height velocity measurements were recorded at 11 spanwise locations for three distances downstream of the turbine array under two inflow conditions. Wake interactions are described in terms of the time‐average streamwise velocity and turbulence intensity as well as the displacement, momentum, and energy thicknesses. The effects of wake merging on power generation are quantified, and the two‐point correlation is used to examine symmetry in the mean velocity between wakes. The results indicate that both asymmetric and rotated wind plant arrangements can produce long‐lasting wakes. At shallow angles, rotated configurations compound the effects of asymmetric arrangements and greatly increase downstream wake persistence.     

水平轴风力机近尾迹流场结构的实验研究

在风洞开口实验段,应用PIV锁相周期采样技术测试风力机近尾迹速度场,通过分析速度场和涡量场,得到近尾迹流场结构特征。近尾迹中存在具有形态特征强烈的叶尖涡结构向下游不断传播。由风轮旋转轴向外,近尾迹的结构组成依次为中央尾迹区、叶尖涡诱导效应区和外部主流区。在叶尖涡诱导效应区内,涡流诱导效应使流场中存在明显的速度增益区和速度亏损区,且增益区和亏损区关于叶尖涡核中心对称。在研究区域内,叶尖涡向下游运动的轴向位移与尖速比成反比,径向位移与尖速比成正比,使叶尖涡诱导效应区影响范围随尖速比的增加径向扩展、轴向缩小。     

格尼襟翼垂直轴风力机风场研究

为研究垂直轴风力机风场中机组气动性能受格尼襟翼的影响,采用TSST湍流模型对直线翼垂直轴风力机进行数值模拟研究。结果表明：风场上游风力机组尖速比越大,机组间流体加速效果越显著,使风力机组气动性能高于单风力机;在中低尖速比时,格尼襟翼可有效提升单个风力机气动效率,在尖速比较高时,提升效果并不明显;在风力机组中安装格尼襟翼且可优化上游风力机组尾迹流场并提高机组间流体的加速效果,使下游风力机获得更高的风能利用率;当格尼襟翼风力机组采用交错排布方式时,下游风力机可利用阻塞效应和格尼襟翼的双重优势,叶片平均切向力较单风力机大幅提升,且风场中3台风力机切向力的平均值高于单台风力机,风场中机组整体性能得到提高。     

雾霾之后的反思

新年过后的第二个周末,浓重的雾霾已在全国多个城市肆虐,这让人们的心情变得糟糕。数据显示,截至1月13日零时,全国有33个城市的部分监测点PM2.5浓度超过300微克/立方米,个别城市出现PM2.5"爆表",比如北京的PM2.5浓度最高达到950微克/立方米。环保专家称,如此严重的空气质量污染,可以说已近人类所能承受的极限。于是,人们看到了政府有关方面发布的紧急预案,比如通知市民减少户外活动,要求学校停止户外体育锻炼,这体现了政府的责任意识。但我们是满足于制定完美的灾情应对预案,还是谋求从根本上消除灾难?     

Wind tunnel investigation on the effect of the turbine tower on wind turbines wake symmetry

In wind farms, the wake of the upstream turbines becomes the inflow for the downstream machines. Ideally, the turbine wake is a stable vortex system. In reality, because of factors like background turbulence, mean flow shear, and tower‐wake interaction, the wake velocity deficit is not symmetric and is displaced away from its mean position. The irregular velocity profile leads to a decreased efficiency and increased blade stress levels for the downstream turbines. The object of this work is the experimental investigation of the effect of the wind turbine tower on the symmetry and displacement of the wake velocity deficit induced by one and two in‐line model wind turbines (,D= 0.9 m). The results of the experiments, performed in the closed‐loop wind tunnel of the Norwegian University of Science and Technology in Trondheim (Norway), showed that the wake of the single turbine expanded more in the horizontal direction (side‐wall normal) than in the vertical (floor normal) direction and that the center of the wake vortex had a tendency to move toward the wind tunnel floor as it was advected downstream from the rotor. The wake of the turbine tandem showed a similar behavior, with a larger degree of non‐symmetry. The analysis of the cross‐stream velocity profiles revealed that the non‐symmetries were caused by a different cross‐stream momentum transport in the top‐tip and bottom‐tip region, induced by the turbine tower wake. In fact, when a second additional turbine tower, mirroring the original one, was installed above the turbine nacelle, the wake recovered its symmetric structure. Copyright © 2017 John Wiley & Sons, Ltd.     

Performance and near wake measurements of a model horizontal axis wind turbine

The performance characteristics and the near wake of a model wind turbine were investigated experimentally. The model tested is a three‐bladed horizontal axis type wind turbine with an upstream rotor of 0.90 m diameter. The performance measurements were conducted at various yaw angles, a freestream speed of about 10 m s ^?1, and the tip speed ratio was varied from 0.5 to 12. The time‐averaged streamwise velocity field in the near wake of the turbine was measured at different tip speed ratios and downstream locations. As expected, it was found that power and thrust coefficients decrease with increasing yaw angle. The power loss is about 3% when the yaw angle is less than 10° and increases to more than 30% when the yaw angle is greater than 30°. The velocity distribution in the near wake was found to be strongly influenced by the tip speed ratio and the yaw angle. At the optimum tip speed ratio, the axial velocity was almost uniform within the midsection of the rotor wake, whereas two strong peaks are observed for high tip speed ratios when the yaw angle is 0°. As the yaw angle increases, the wake width was found to be reduced and skewed towards the yawed direction. With increasing downstream distance, the wake velocity field was observed to depend on the tip speed ratio and more pronounced at high tip speed ratio. Copyright © 2011 John Wiley & Sons, Ltd.     

LiDAR measurements for an onshore wind farm: Wake variability for different incoming wind speeds and atmospheric stability regimes

Wind measurements were performed with the UTD mobile LiDAR station for an onshore wind farm located in Texas with the aim of characterizing evolution of wind‐turbine wakes for different hub‐height wind speeds and regimes of the static atmospheric stability. The wind velocity field was measured by means of a scanning Doppler wind LiDAR, while atmospheric boundary layer and turbine parameters were monitored through a met‐tower and SCADA, respectively. The wake measurements are clustered and their ensemble statistics retrieved as functions of the hub‐height wind speed and the atmospheric stability regime, which is characterized either with the Bulk Richardson number or wind turbulence intensity at hub height. The cluster analysis of the LiDAR measurements has singled out that the turbine thrust coefficient is the main parameter driving the variability of the velocity deficit in the near wake. In contrast, atmospheric stability has negligible influence on the near‐wake velocity field, while it affects noticeably the far‐wake evolution and recovery. A secondary effect on wake‐recovery rate is observed as a function of the rotor thrust coefficient. For higher thrust coefficients, the enhanced wake‐generated turbulence fosters wake recovery. A semi‐empirical model is formulated to predict the maximum wake velocity deficit as a function of the downstream distance using the rotor thrust coefficient and the incoming turbulence intensity at hub height as input. The cluster analysis of the LiDAR measurements and the ensemble statistics calculated through the Barnes scheme have enabled to generate a valuable dataset for development and assessment of wind farm models.     

基于CFD的二维垂直轴风力机性能计算

采用计算流体力学方法(CFD)针对垂直轴风力发电机,开展简化的二维绕流特性研究。首先,基于开放型转子和增强型转子,研究网格节点数和壁面y+、计算时间步长和湍流模型等的变化对计算结果的影响,对计算模型和方法进行确认。随后,计算分析增强型垂直轴风力机与开放型垂直轴风力机的特性。结果表明,与开放性垂直轴风力发电机相比,增强型垂直轴风力发电机的功率系数和转矩系数有明显增加,且达到最大值的位置向叶尖速比增大的方向移动。然后对增强型垂直轴风力机发电机在不同来流风速下进行计算,发现增强型垂直轴风力发电机的转子转矩随来流风速增加,而转矩系数和功率系数与来流风速无关。最后,针对定子叶片在不同的方向开展计算研究。结果表明,定子叶片在不同方向时,增强型垂直轴风力机的转子转矩不同,且转矩到达峰值的位置也不同;在当前3个方向角中,叶片处于0°方向角时风力机具有最高的转矩系数,即具有最佳的功率系数。     

Upwind preview to a horizontal axis wind turbine: a wind tunnel and field‐scale study

Data collected at the Eolos wind research facility and in the Saint Anthony Falls Laboratory atmospheric boundary layer wind tunnel are used to study the impact of turbulent inflow conditions on the performance of a horizontal axis wind turbine on flat terrain. The Eolos test facility comprises a 2.5MW Clipper Liberty C96 wind turbine, a meteorological tower and a WindCube LiDAR wind profiler. A second set of experiments was completed using particle image velocimetry upwind and in a wake of a miniature turbine in the wind tunnel to complement LiDAR measurements near the Eolos turbine. Joint statistics, most notably temporal cross‐correlations between wind velocity at different heights and turbine performance, are presented and compared at both the laboratory and field scales. The work (i) confirms that the turbine exerts a blockage effect on the mean flow and (ii) suggests a key, specific elevation, above hub height, where the incoming velocity signal is statistically most relevant to turbine operation and control. Wind tunnel measurements confirm such indication and suggest that hub height velocity measurements are optimal for wind preview and/or as input for active control strategies in aligned turbine configurations. Copyright © 2015 John Wiley & Sons, Ltd.