风力机桨叶结构振动特性有限元分析

假设风力机叶片是一个末端固支的悬臂梁结构,以有限元方法建立风力机叶片的振动方程,以实际的风力机７ＦＤ－２００为例,应用国际通用的大型有限元分析程序ＡＬＧＯＲ－ＦＥＡＳ,对其振动特性进行分析。ＢＯＲＬＡＮＤＣ３．１语言为编程工具,在ＡｕｔｏＣＡＤ１２ｆｏｒ ＷｉｎＡＤＳ Ｄｅｖｅｌｏｐｍｅｎｔ环境下开发了简便易用的前处理模块,自动生成叶片的有限元网格图。在计算中,把风力机叶片的振动分为垂直于旋转平面     

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。     

垂直轴风力机改进翼型气动及功率特性研究

为提高垂直轴风力机的风能利用率,基于CFD数值模拟技术,分析了常用典型垂直轴风力机翼型的气动及功率特性,并以NACA0012翼型为基础对其进行改进。对比改进前后翼型表明,增大翼型厚度可降低升阻比,增大翼型弯度可增强其失速特性;厚尾缘翼型、升阻互补型翼型可分别降低翼型失速性能、增加启动力矩,其中厚尾缘翼型的H型垂直轴风力机的功率系数较大,可提高风能利用率,为翼型优化设计提供了新思路。     

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%。     

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。     

立轴风力机叶片动态失速特性与气动性能分析

结合立轴风力机运行时叶片的非定常气动特性,对B-V、B-L和ONERA动态失速模型进行适当简化和修正,结合实验数据对比分析俯仰运动时动态失速对翼型气动特性的影响。在双盘多流管气动分析方法的基础上,结合修正的动态失速模型,对Sandia 17m风力机进行气动性能计算,比较不同模型对叶片非定常气动特性的评价结果,与实测气动载荷和功率对比表明,B-L模型整体上对立轴风力机气动性能预测较好。     

水平轴风力机翼型设计与动态失速数值模拟

利用XFOIL软件对水平轴风力机叶片的参考翼型进行了改进设计,通过数值模拟的方法评估获得:所设计的翼型优于参考翼型,满足设计要求;由于风力机叶片在动态失速时的特性较为复杂,该文针对某一个设计翼型进行了动态失速的数值模拟,使用FLUENT软件编写用户函数,获得漩涡产生、发展和脱落规律,比较翼型在动态和稳态的升力和阻力特性,并提出了考虑失速效果的风轮气动设计和性能改进的意见.     

水平轴风力机静态失速特性

采用叶片表面边界层理论分析,三维旋转流场的数值模拟以及实验风力机模型的流动测量方法对水平轴风力机的静态失速特性进行了较为系统的研究。研究表明,旋转速度使得实际三维旋转风轮翼型表面的静压分布与二维非旋转条件下翼型表面静压分布产生较大差别,这是造成静态失速的原因之一。     

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.     

覆冰对风力机专用翼型气动性能影响的数值研究

利用商用CFD软件和S-A湍流模型,对风力机常用的NREL S809翼型在不同覆冰形态、覆冰厚度下的静态流场和动态流场进行了数值计算,得到了Re=1×106时各种覆冰情况下该翼型的气动性能,并研究了不同的覆冰形态对风力机翼型静态、动态失速特性的影响.结果表明：向吸力面生长的覆冰形态会造成覆冰层后的分离涡,随着攻角的增加分离涡向后缘生长,造成升力系数的较大下降,阻力系数增加;沿弦向生长的覆冰对尾缘分离涡的生成影响较小;在动态失速情况下,翼型周围流场比较复杂,覆冰形态对翼型升力系统的影响规律也较复杂;从静态流场特性分析,覆冰破坏了翼型的流线从而直接影响了翼型的气动性能;从动态流场特性分析,覆冰改变了翼型动态升力系数曲线的斜率从而影响到风力机的气动弹性稳定性.     

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.     

失速延迟模型在风力机预测中的应用

对风力机性能特别是最大输出功率的准确预测有助于在设计时提高其整体的经济性,但静态失速延迟给性能预测带来了一定的难度。通过使用预定尾迹的升力线改进法结合静态失速模型对风力机在不同的来流风速下的性能进行预测,可以提高预测的准确性。通过刚性尾迹和预定尾迹的升力线改进法对风力涡轮性能的相应分析,表明预定尾迹及静态失速延迟模型的升力线改进法可以较准确地预测风力涡轮的性能,尤其是风力机叶片在失速附近的工作状况。     

非线性双方程湍流模型用于翼型分离流动模拟

采用非线性k-ε和q-ω双方程湍流模型,利用高收敛率、高精度和高分辨率的数值算法,对二维NRELS809翼型在0～18°攻角范围内的低速绕流进行了数值模拟,将翼型的升阻特性的计算值与实验值进行了比较。与采用线性k-ε和q-ω双方程湍流模型的计算结果对比表明,当翼型流动发生分离时,采用非线性双方程湍流模型可以明显地改进计算精度。本文采用的数理模型与数值方法可有效地用于风力机翼型大尺度分离流场的预测。     

带失速延迟模型的改进型升力线法预测风力机性能

采用带Du-Selig静态失速延迟模型的改进升力线法对风力机不同来流风速下的性能进行预测,静态失速延迟模型可以弥补对输出功率的低估;还分析了来流风速在7.0~10.0m/s时沿径向的攻角分布以及有无失速延迟模型时的升阻力系数分布。通过比较发现在中间叶高处出现最大攻角,相应地在该叶高位置最先发生流动分离。     

On the free yaw behaviour of horizontal axis wind turbines

Torque associated with rotor stall is shown to be an important factor in the yaw behaviour of fixed pitch horizontal axis wind turbines (HAWT). For a given operating machine, the best performance occurs when the plane of rotation is perpendicular to the wind velocity for all wind speeds, V, less than a fixed value, V₀. For V > V₀ a velocity dependent torque yaws a free rotor to more efficient energy gathering positions provided the yaw torque exceeds the corresponding machine frictional torque. The optimum angular positions (yaw trajectories) computed from dynamic equilibrium considerations are compared with, and shown to be in satisfactory agreement with, solutions furnished by a model based on a postulated energy gathering function. The postulational approach developed is particularly useful because of its generality and simplicity in describing the performance of a HAWT. It is noted that although it is advantageous from a performance point of view to yaw the rotor to the optimum position corresponding to a given wind velocity established by either dynamic equilibrium or the energy gathering model, one must be aware of the accompanying increase in cyclic loading. On the other hand, maintaining the plane of rotation perpendicular to the wind velocity at all times could result in significant performance losses as well as fatigue problems in fixed pitch rotors, especially during stall conditions.     

风力机翼型大迎角分离和动态失速的数值研究

通过求解非定常、不可压缩雷诺平均的Navier-stokes方程和SST k-ω双方程湍流模型,数值预测了LS0413翼型在0°～360°迎角范围内大尺度分离与失速流场特性。并对该翼型的动态失速特性进行了数值模拟,典型的正弦振荡计算结果表明:1)SST k-ω湍流模型能够较好地模拟翼型升力和阻力系数的迟滞环变化趋势;2)绕翼型的流场结构在轻失速和深失速下存在明显的差别。     

A simple model for deep dynamic stall conditions

The present study is focused on modeling of dynamic stall behavior of a pitching airfoil. The deep stall regime is in particular considered. A model is proposed, which has a low implementation and computational complexity but yet is able to deal with different types of dynamic stall conditions, including those characterized by multiple vortex shedding at the airfoil leading edge. The proposed model is appraised against an extensive data set of experimental (α,C_L) curves for NACA0012. The results of an existing widely used model, having comparable complexity, are also shown for comparison. The proposed model is able to well reproduce not only the classic curves of deep dynamic stall but also the curves characterized by lift oscillations at high angles of attack due to the shedding of multiple vortices. Furthermore, the model appears to be robust to variations of its parameters from the optimal values and of the airfoil geometry. Finally, the model is successfully implemented in a commercial CFD software and applied to the simulation of a vertical axis wind turbine within the actuator cylinder approach. The accuracy of the prediction of the turbine power coefficient in the whole rotation cycle is very good for the optimal working condition of the turbine, for which the model parameters were calibrated. Fairly good accuracy is also obtained in significantly different working conditions without any further calibration.     

A stochastic model for the simulation of wind turbine blades in static stall

The aim of this work is to improve aeroelastic simulation codes by accounting for the unsteady aerodynamic forces that a blade experiences in static stall. A model based on a spectral representation of the aerodynamic lift force is defined. The drag and pitching moment are derived using a conditional simulation technique for stochastic processes. The input data for the model can be collected either from measurements or from numerical results from a Computational Fluid Dynamics code for airfoil sections at constant angles of attack. An analysis of such data is provided, which helps to determine the characteristics of stall. The model is applied to wind turbine rotor cases, including the stand still condition, and results are compared to experimental data. Copyright © 2009 John Wiley & Sons, Ltd.     

Aerodynamic response of an airfoil section undergoing pitch motion and trailing edge flap deflection: a comparison of simulation methods

The study presents and compares aerodynamic simulations for an airfoil section with an adaptive trailing edge flap, which deflects following a smooth deformation shape. The simulations are carried out with three substantially different methods: a Reynolds‐averaged Navier–Stokes solver, a viscous–inviscid interaction method and an engineering dynamic stall model suitable for implementation in aeroelastic codes based on blade element momentum theory. The aerodynamic integral forces and pitching moment coefficients are first determined in steady conditions, at angles of attack spanning from attached flow to separated conditions and accounting for the effects of flap deflection; the steady results from the Navier–Stokes solver and the viscous–inviscid interaction method are used as input data for the simpler dynamic stall model. The paper characterizes then the dynamics of the unsteady forces and moments generated by the airfoil undergoing harmonic pitching motions and harmonic flap deflections. The unsteady aerodynamic coefficients exhibit significant variations over the corresponding steady‐state values. The dynamic characteristics of the unsteady response are predicted with an excellent agreement among the investigated methods at attached flow conditions, both for airfoil pitching and flap deflection. At high angles of attack, where flow separation is encountered, the methods still depict similar overall dynamics, but larger discrepancies are reported, especially for the simpler engineering method. Copyright © 2014 John Wiley & Sons, Ltd.     

振荡扰流提高风力机翼型气动性能的研究

利用振荡扰流进行了改善风力机翼型大攻角下性能的研究。应用有限体积法，数值模拟了头部附加振荡扰流的翼型分离流动，并对振荡扰流增升效果的参数影响进行了分析。结果表明在深失速条件下，翼型头部附加的振荡扰流在一定的频率和振幅时能够显著改善翼型的气动性能，提高翼型的升力。与扰流振幅相比，调节扰流振荡频率更能改善翼型深失速条件下的气动性能。