水平轴风力机失速延迟特性及其力学机理的研究

建立简化的风力机模型,研究了风力机叶片翼型表面的压力分布及升力系数的分布,并与静态实验数据相比较,成功模拟了旋转所造成的失速延迟现象.通过计算离心加速度和哥氏加速度在叶片表明边界层内的分布,在叶片展向不同位置,两者在数量上具有相同的量级,但是哥氏力的大小与失速程度有关.比较两者对翼型失速延迟作用的差异,从数量上解释了三维翼型形成展向流的原因和失速延迟的机理.     

偏航工况下风力机动态失速特性的数值模拟

采用基于滑移网格模型的三维非稳态CFD方法,对NREL Phase VI风力机在偏航工况下的动态失速特性进行计算,分析旋转周期内翼型攻角和升力系数的变化,并进一步分析非稳态流动对动态失速的影响。结果表明:偏航工况时,来流风的水平分量和翼型的非稳态绕流会延缓气流分离涡的形成和失速现象的发生,伴随的动态失速现象会显著增加叶片的动态负荷;越靠近叶根动态失速特征越明显,翼型承受的非稳态升力系数最大可达静态升力系数的5倍以上,升力系数迟滞环面积也更大。计算结果能够为风力机优化设计和运行提供理论指导。     

考虑风剪切的1.3MW风力机整机三维定常流动数值研究

分别采用均匀风和剪切风对1.3 MW失速调节风力机整机在8 m/s和13 m/s来流风速下的绕流流场进行全三维定常数值模拟。根据模拟结果分析叶片不同截面的压力系数分布、沿叶展方向的功率分布、风轮三维流场细节、风轮下游不同距离处的静压分布和二维相对速度矢量分布情况。结果表明：剪切风下,风力机功率计算值与设计值吻合较好;在靠近叶根处,适当地减小有效攻角可提高翼型气动性能,选择适应较大攻角的翼型,可以提高叶根处的输出功率;在靠近叶尖的部位,适当增加有效攻角,同时选择适应小攻角的翼型可以提高叶尖处的输出功率;在叶根部位,发生了明显的流动分离;塔架与轮毂所在位置的下游尾迹处产生的漩涡和干扰要远远大于叶轮面其他部位。     

考虑层流分离的低速风力机翼型气动性能研究

以风力机DU93-W-210翼型为研究对象,采用数值计算与实验验证方法研究了低雷诺数(2×105~5×105)下翼型升阻气动性能,基于修正转捩模型分析了多雷诺数多攻角下翼型层流分离泡对气动性能的影响.结果表明:基于四方程转捩模型Transition SST计算所得升阻力系数及翼型表面转捩位置与实验值接近,低雷诺数流动计算适用性较好;雷诺数越小,翼型层流分离泡越明显,翼型升阻比越小;失速前雷诺数对翼型升阻比影响较大而失速后影响较小,且雷诺数越小该翼型失速越缓和;攻角越大,翼型上表面层流分离泡越靠近前缘而下表面越靠近尾缘;失速前上表面和下表面转捩位置均呈线性变化,失速后上表面转捩位置呈非线性变化.     

凹槽-襟翼对翼型动态失速特性影响研究

风力机复杂运行环境使叶片常处于失速环境,导致翼型升力骤降,严重影响风力机气动性能.为改善翼型流动分离,延缓失速,对凹槽-襟翼对翼型动态失速特性作用效果开展研究,并利用计算流体力学方法分析不同折合频率与翼型厚度时凹槽-襟翼对翼型气动性能的影响.结果表明:俯仰振荡过程中,凹槽-襟翼可有效提升翼型吸力面流速,降低失速攻角下逆...     

风力机振荡翼型动态失速特性的CFD研究

为采用CFD方法研究风力机振荡翼型出现的流动动态失速现象,首先依据实验结果,对比分析了Baldwin-Lomax、Johnson-King、K-ωSST、S-A和K-ω5种紊流模型计算结果,结果表明:K-ωSST模型由于考虑到分离流动的非平衡作用,针对动态失速的计算精度较高。通过对NACA0012翼型振荡运动的流场进行计算,详细分析了振荡运动过程中翼型表面分离涡的形成、放大直至造成翼型失速以及失速区涡结构。     

水平轴风力机叶片翼型结冰的数值模拟

通过计算流体力学(CFD)的方法对水平轴风力机桨叶翼型的霜状积冰进行了数值模拟。模拟采用四阶龙格-库塔法求解水滴运动轨迹,假定水滴在与叶片相碰撞的点处完全凝结,并且冰沿着翼型表面法向方向增长,通过模拟得到了某风力机厂家提供翼型在不同时间段叶片表面结冰后形成的冰形,同时利用FLUENT软件模拟了风力机叶片翼型周围流场的变化,并与结冰前该翼型的气动性能进行了对比。研究结果表明与干净翼型相比,在模拟气象条件下的结冰翼型的最大升力系数大约减少了27%,阻力系数增加了约38%,失速攻角降低了4°。根据模拟可以认为,结冰后翼型提前进入失速区是造成桨叶气动性能恶化的主要原因。     

水平轴风力机翼型动态失速特性的数值研究

动态失速对水平轴风力机的运行性能影响很大，大量的实验和分析显示，水平轴风力机在动态失速工况下其运行载荷将增长50～100％，而风力机翼型的动态失速特性是分析水平轴风力机动态失速特性的基础。本文应用CFD软件Fluent6．0对NREL S809翼型的二维动态流场进行了数值模拟，得到了翼型攻角在9*～31*范围内按正弦周期变化时的绕流流场。计算结果显示：动态失速下翼型的绕流流场与相同工况下的静态绕流流场有着十分明显的差别，同时也引起翼型升力、阻力系数的显著变化。     

垂直轴风力机动态流场及其气动性能分析

垂直轴风力机气动性能研究是风力机设计、实验的重要部分,对其运动状态下的流场进行分析是观测垂直轴风力机性能重要环节.基于NACA0012对称翼型,建立二维几何模型并进行模拟计算.采用k-ωSST湍流模型及滑移网格技术,通过CFD软件数值计算得到达里厄型直叶片垂直轴风力机运行时周边流场分布情况.通过比较不同方位角下流场涡量以及升、阻力系数得出:在方位角为105°附近时,翼型下表面产生流动分离,并导致失速;下风区翼型运行的流场由于受到上风区尾流的影响,翼型周围没有产生明显的流动分离.     

基于Theodorsen理论的新型动态失速预测模型及其应用

风力机叶片动态失速时的非定常气动特性及严重的迟滞现象使得风力机功率实测值严重偏离其静态预测值。鉴于此,基于Theodorsen理论、基尔霍夫势流理论,在忽略低阶附加质量引起的下洗气流加速度项及状态变量转换后,提出一种包括翼型附着流和后缘动态分离流的新型动态失速模型。利用该模型分析NREL 5 MW海上风力机叶片6种翼型的非定常动态失速特性得出：通过翼型的气流在完全附着流与完全分离流之间不断转换,受附着流脱落尾诱导的动态下洗气流影响及边界层动态分离产生的压力滞后的双重作用,动态升力系数变化曲线和静态升力现象曲线偏差较大,6种翼型动态升力系数变化曲线均呈非常明显的迟滞环现象。DU40、DU35、DU30、DU25、DU21和NACA64这6种翼型动态升力系数增幅明显,分别达17.6%、60.9%、60.7%、55.1%、63.7%和40.8%。动态失速攻角极大地超过静态失速攻角,分别增大到36.53°、21.40°、20.20°、17.68°、16.97°和21.42°。6种翼型动态失速预测结果与公开实验数据结论一致,证实所提出的动态失速气动模型计算结果准确可信,具有较强通用性。     

A study on stall-delay for horizontal axis wind turbine

The study on the stall-delay phenomenon for horizontal axis wind turbine (HAWT) was carried out by employing the boundary layer analysis, the numerical simulation and the experimental measurement. The effects of rotation on blade boundary layers are investigated by solving the 3D integral boundary layer equations with assumed velocity profiles. It is shown that rotation has a generally beneficial effect in delaying separation compared with that under 2D stationary condition. Next, the detailed flow fields are simulated on the conditions of 2D stationary and 3D rotation by CFD code. The computation results show that rotation affects the pressure distribution on the surface of the foil, which can give rise to 3D stall-delay in stalled condition HAWT. Finally, the flow fields behind a model HAWT are measured with a hot-wire probe in the wind tunnel. The results show good agreement with those from 3D computation calculations, suggesting that the stall-delay should be taken into consideration, in order to accurately predict the loading and performance of a HAWT operating in stall.     

The effect of rotation on the boundary layer of a wind turbine blade

Design and analysis methods for wind turbines are presently based on relatively simple models of rotor blade aerodynamics, such as 2-D blade element/momentum theory (BEMT). Field investigations over the past few years have shown discrepancies between predicted and measured performance, owing to the effect of rotation on the wind turbine blade boundary layer distribution. The present paper is aimed at describing a fundamental phenomenon: the effect of rotation on the blade boundary layer of a wind turbine. In this paper, 3-D incompressible steady momentum integral boundary layer equations are employed to study this complex problem. By solving the 3-D integral boundary layer equations with the assumed velocity profiles and a closure model (including both laminar and turbulent boundary layer models), the effects of rotation on blade boundary layers are investigated. Several key parameters, such as separation position and momentum thickness, are calculated and compared for the rotation and non-rotation cases. It is concluded that the stall is postponed due to rotation and the separation point is delayed as a result of increasing rotation speed or decreasing blade spanwise position. Possible modifications that should be considered to the existing 2-D BEMT method are suggested.     

旋转对风力涡轮叶片三维边界层影响的数值计算

由于旋转的影响,基于经典二维叶素理论设计的水平轴风力涡轮叶片,在高风速工况下不能可靠运行,即存在失速延迟现象,采用不可压缩三维边界层积分方程揭示产生这种失速延迟现象的机理,分析旋转对风力涡轮边界层的影响,通过积分边界层方程的求解（包括层流,转捩及紊流）,得到一些关键的影响参数（如失速点位置,动量厚度等）。并在相同的运行条件下,比较二维工况与三维旋转工况下各关键参数的差别,得到由于旋转的影响,边界层     

风力机叶片失速延迟现象分析与修正研究

随着经济的发展,各国越来越重视清洁能源,因此风力发电技术得到了很大的提高,对风力发电的研究也越来越深入.由于旋转效应的存在,使得风力机叶片的失速发生了延迟.旋转引起边界层的失速延迟使得基于二维叶素理论的风轮机设计和性能预估方法得到的估算值较实际功率输出值偏小,为此近年来许多学者进行深入研究,并建立了几种失速延迟修正模型.应用四种模型对实验风力机气动特性进行计算,将计算结果与实验结果作比较,并讨论了这些模型的误差特点及适用范围.     

On the quasi-instantaneous aerodynamic load and pressure field measurements on turbines by non-intrusive PIV

An experimental technique is presented to non-intrusively measure the quasi-instantaneous aerodynamic loads and surrounding pressure field for a turbine by using particle image velocimetry (PIV). The PIV measurements provide the velocity flow field needed to calculate the pressure field around the turbine using three different methods. In the first method, the quasi-instantaneous and mean pressure fields are obtained by solving the Poisson equation and by calculating the boundary conditions from the Navier–Stokes equations. In the second method, the pressure at the boundaries is determined by spatial integration of the pressure gradient. In the third method, the pressure is calculated using the Bernoulli equation. The experimental results are compared to aerodynamic load theoretical predictions from the Blade Element Momentum theory (BEM). An analysis of the experimental results showed the importance of the local acceleration, convective and pressure terms when calculating the forces and the pressure field in a stationary reference frame. Only the Poisson method includes all these terms, and had a small standard deviation between the calculated instantaneous forces. Furthermore, the Poisson method results are independent of the control volume size investigated while the other two experimental methods are affected. This experimental technique could be used to simultaneously replace instrumentation such as force balance and pressure taps while providing for the first time quasi-instantaneous information about the surrounding flow in any turbine immersed in an incompressible flow. In addition, it could be applied to evaluate unsteady wind loads and aerodynamic stall and also provide much needed information for validating computational studies.     

An insight into the separate flow and stall delay for HAWT

The flow characteristics and the stall delay phenomenon of wind turbine rotor due to blade rotation in the steady state non-yawed conditions are investigated. An incompressible Reynolds-averaged Navier–Stokes solver is applied to carry out all the cases at different wind speeds from 5 m/s to 10 m/s with an interval of 1 m/s. CFD results turn out to agree well with experimental ones at incoming wind speeds below 10 m/s, though at 10 m/s some deviations exist due to the relative large flow separation and 3D spanwise flow over the suction surface of the blade. In the meanwhile, a lifting surface code with and without Du–Selig stall delay model is used to predict the power. A MATLAB code is developed to extract aerodynamic force coefficients from 3D CFD computations which are compared with the 2D airfoil wind tunnel experiment to demonstrate the stall delay and augmented lift phenomenon particularly at inboard span locations of the blade. The computational results are compared with the corrected value by the Du–Selig model and a lifting surface method derived data based on the measurements of the Unsteady Aerodynamic Experiment at the NASA Ames wind tunnel.     

定常吸气对垂直轴风力机性能影响研究

定常吸气装置可有效提高垂直轴风力机气动性能,改善风轮流场结构及翼型动态失速特性.基于CFD方法对垂直轴风力机进行数值模拟,研究不同叶尖速比(TSR)下定常吸气对风力机气动及流场特性的影响,对比分析原始风力机及定常吸气作用下的风能利用率、整机转矩系数及涡量分布.结果表明:不同尖速比下定常吸气均可显著提高风力机气动性能,减...     

仿鸮翼非光滑前缘对风力机叶片气动性能的影响

经过数百万年的进化,鸮形目鸟类在其飞行行为上显现出许多优异的特征。文章选取鸮翼的非光滑前缘作为仿生对象,设计出一种仿生风力机叶片,并分析非光滑前缘结构对风力机叶片气动性能的影响。采用S-A湍流模型,对低雷诺数下原型风力机叶片和仿生风力机叶片进行绕流流场模拟。模拟结果表明,在大攻角下,仿生风力机叶片的前缘凸起能够改变气流在叶片表面的流向分布,使气流在吸力面仍保持附着流动,进而减少叶片吸力面的失速区,有效延缓叶片失速现象的发生,从而使得仿生风力机叶片的失速角比原型风力机叶片的失速角推迟了10°左右,改善了风力机叶片的气动性能。     

New vortex‐lift and tangential‐force models for HAWT aerodynamic load prediction

Horizontal axis wind turbines (HAWTs) experience three‐dimensional rotational and unsteady aerodynamic phenomena at the rotor blades sections. These highly unsteady three‐dimensional effects have a dramatic impact on the aerodynamic load distributions on the blades, in particular, when they occur at high angles of attack due to stall delay and dynamic stall. Unfortunately, there is no complete understanding of the flow physics yet at these unsteady 3D flow conditions, and hence, the existing published theoretical models are often incapable of modelling the impact on the turbine response realistically. The purpose of this paper is to provide an insight on the combined influence of the stall delay and dynamic stall on the blade load history of wind turbines in controlled and uncontrolled conditions. New dynamic stall vortex and nonlinear tangential force coefficient modules, which integrally take into account the three dimensional rotational effect, are also proposed in this paper. This module along with the unsteady influence of turbulent wind speed and tower shadow is implemented in a blade element momentum (BEM) model to estimate the aerodynamic loads on a rotating blade more accurately. This work presents an important step to help modelling the combined influence of the stall delay and dynamic stall on the load history of the rotating wind turbine blades which is vital to have lighter turbine blades and improved wind turbine design systems.