自由涡尾迹方法中涡核尺寸对风力机气动计算的影响

涡核模型中的涡核尺寸对自由涡尾迹(free vortex wake, FVW)方法准确预估风力机气动特性至关重要,涡核尺寸包括初始涡核半径和由于耗散效应涡核半径在尾迹中的增长. FVW方法中涡线控制方程离散采用三步三阶预估校正格式,涡核模型采用经典Lamb-Oseen模型,并考虑了涡耗散效应和拉伸效应.首先,通过气动载荷和叶尖涡涡量平均值的分析得到初始涡核半径的取值范围;然后,根据叶尖涡耗散特性的分析,确定体现涡黏性耗散效应涡核半径增长的经验常数的取值;最后,分析了涡核尺寸对叶尖涡结构的影响,进一步验证初始涡核半径和涡黏性耗散经验常数的取值对风力机气动计算的影响.结果表明:当初始涡核半径大于50%弦长时,FVW方法收敛稳定且能准确预估风轮气动载荷;综合风轮气动载荷和叶尖涡耗散特性,初始涡核半径取60%到70%弦长为宜,且对应的涡黏性耗散经验常数取值也不同;风轮气动载荷和叶尖涡结构的准确预估主要受初始涡核半径影响,经验常数对其影响不大,而经验常数主要影响风轮下游尾流场叶尖涡的耗散特性.     

一种风力机气动计算的全自由涡尾迹模型

采用全自由方式建立风力机尾流场的涡尾迹模型,引入“虚拟周期”的概念,并发展一种自适应松弛因子方法,从而改善了自由尾迹迭代的稳定性,提高了迭代收敛速度。利用建立的自由涡尾迹模型,计算了风力机叶片的尾流场结构、气动性能及叶片载荷,并与实验结果进行了对比分析。结果表明,尖速比越大,自适应松弛因子方法对缩小模型计算时间越有效;全自由涡尾迹模型能准确给出风力机尾流场的结构,包括尾迹的扩张以及叶尖涡和叶根涡的产生、发展和耗散的过程,风轮扭矩与实验数据吻合;叶片载荷分布的计算结果在低风速下与实验值基本一致,但是在大风速下差别较大,说明需要一个准确的失速模型。     

风剪切对风力机叶片气动性能及尾迹形状的影响

风力机通常运行在非定常工况中,其气动性能及尾迹会随着工况的变化而变化.风剪切是风力机长期所处的环境,它会影响到叶片气动载荷、尾迹形状、总体性能等,分析风剪切作用下的叶片气动性能对风力机的设计有重要意义.本文采用一种时间步进自由涡尾迹(free vortex wake,FVW)方法,耦合FVW方法与风剪切模型,计算不同风...     

复杂工况下的大型风力机气动性能和尾迹研究Investigation of aerodynamic performance and wake of the large scale wind turbine in complicated conditions

在复杂工况下,大型风力机非定常特性会更严重,导致风力机气动性能变化和尾迹预测更加复杂。本文主要针对稳态偏航、动态偏航、风剪切和随机风速场等复杂工况,基于自由涡尾迹方法,嵌入复杂工况的模块,加入了动态失速模型和三维旋转效应模型修正,实现了复杂工况数值模拟计算,比较了不同复杂工况的气动载荷和尾迹形状。最后,得出了风力机在复杂工况下的气动性能、载荷和尾迹叶尖涡线特性,并计算出风力机在复杂工况下的气动载荷超调量和迟滞时间。对推进自由涡尾迹方法应用于风力机工程的大批工况载荷计算,提高大型风力机的载荷计算精度和设计水平等具有重要意义。     

基于涡尾迹方法的风力机气动性能分析

基于(势流)涡尾迹方法开发了水平轴风力机叶片气动性能分析程序,采用固定尾迹涡模型和自由尾迹模型分别对气动设计性能进行计算分析,得到风力机设计工况下的涡位置、诱导因子、功率系数及扭矩系数等气动性能参数,并与设计结果对比。结果表明,涡尾迹方法能够快速准确地计算风力机叶片气动性能参数,对风力机叶片气动分析,固定尾迹涡模型较自由尾迹模型计算时间短,具有较好的实用性。     

复杂工况下的大型风力机气动性能和尾迹研究

在复杂工况下,大型风力机非定常特性会更严重,导致风力机气动性能变化和尾迹预测更加复杂。本文主要针对稳态偏航、动态偏航、风剪切和随机风速场等复杂工况,基于自由涡尾迹方法,嵌入复杂工况的模块,加入了动态失速模型和三维旋转效应模型修正,实现了复杂工况数值模拟计算,比较了不同复杂工况的气动载荷和尾迹形状。最后,得出了风力机在复杂工况下的气动性能、载荷和尾迹叶尖涡线特性,并计算出风力机在复杂工况下的气动载荷超调量和迟滞时间。对推进自由涡尾迹方法应用于风力机工程的大批工况载荷计算,提高大型风力机的载荷计算精度和设计水平等具有重要意义。     

单一水平轴风电机组尾迹的模拟方法与流动机理研究综述

为实现碳达峰、碳中和“3060”目标, 风能将在我国能源体系发挥重要作用. 风力机尾迹是影响风电性能和度电成本的关键因素, 需在风力机布置和控制设计中充分考虑. 本文首先介绍风力机尾迹的数值模拟方法, 包括解析模型、低阶模型、大涡模拟和来流湍流生成方法. 解析模型和低阶模型可快速计算风力机尾迹, 但依赖于模型参数, 且不能或不能准确预测尾迹湍流特性. 结合风力机参数化模型的大涡模拟可准确预测尾迹蜿蜒等湍流特征, 是流动机理研究的有力工具, 可为发展快速预测模型提供数据和理论支撑. 接着, 本文介绍了叶尖涡、中心涡和尾迹蜿蜒并讨论其产生机理. 对于湍流来流, 叶尖涡主要存在于近尾迹. 蜿蜒是远尾迹的主要特征, 影响下游风力机的来流特征. 尾迹蜿蜒的产生有两种机制: 来流大尺度涡和剪切层失稳. 数值和观测结果显示两种机制共同存在. 机舱和中心涡对尾迹蜿蜒有重要影响. 采用叶片和机舱的致动面模型可准确预测尾迹蜿蜒. 研究显示不同风力机尾迹间的湍流特征存在相似性, 为发展尾迹湍流的快速预测模型提供了理论依据. 当前研究多关注平坦地形上的风力机尾迹, 复杂地形和海洋环境下的大气湍流和风力机尾迹的机理复杂, 现有工程模型无法准确预测, 有待深入研究.      

考虑气核生长溃灭效应的螺旋桨梢涡空化初生数值模拟研究

梢涡空化是螺旋桨最早发生的空化类型,其一旦发生会显著增强舰船辐射噪声水平.因此,螺旋桨梢涡空化初生的预报是军舰临界航速确定的关键,长期以来受到船舶领域诸多专家学者的重点关注.微观气核受涡心低压作用而发生暴发式生长是梢涡空化初生的重要机制,而传统欧拉框架下的宏观空化模型用经验参数模化了微观气核的影响而无法对该过程准确模拟,影响对螺旋桨空化初生的准确预报.为了弥补传统模拟方法的不足,本研究发展并使用一种基于气泡动力学并考虑水相可压缩效应的欧拉-拉格朗日空化初生数值预报方法对螺旋桨梢涡空化初生进行了数值模拟研究.与实验结果对比表明,该模型能够准确地预报螺旋桨梢涡空化初生.此外,本研究不仅从微观气核角度探究不同来流气核尺寸对空化初生的影响,还进一步研究梢涡流动特性对气核演变的影响机制,初步探究初生空化在螺旋桨梢涡流场中的发声机理.在空化初生光学判断准则下尺寸越大的气核越容易被梢涡捕获而暴发式生长.气核在梢涡卷吸作用下逐渐靠近涡心低压区.在涡心低压区的持续作用下气核开始暴发式生长,并在半径达到最大后迅速收缩溃灭,产生强烈的正声压脉冲信号.     

涡波一体乘波飞行器宽速域气动优化设计研究

涡波一体宽速域乘波飞行器通过在低速引入涡效应,显著改善了传统乘波体在低速状态下的升阻特性,具有在未来宽速域空天飞行器总体气动设计当中得到广泛应用的巨大潜力.但是,该设计方法的研究尚不完善,特别是在基准流场建立过程中忽略了三维效应、低速效应、黏性效应以及头部/前缘的钝化效应,因此其高低速气动特性均有优化设计的空间.针对此问题,本文结合高保真RANS求解器、自由变形参数化方法、鲁棒的结构网格变形方法、离散伴随方法以及序列二次规划算法,发展了基于离散伴随的宽速域飞行器气动优化设计方法.基于上述方法,针对涡波一体乘波飞行器开展了兼顾低速与高超声速气动性能的三维整机气动优化设计研究,获得了宽速域优化构型并对其进行了流动机理分析.结果表明,相较于初始构型,宽速域优化构型可以将飞行器高超声速状态下升阻特性略微提升的同时,显著增强低速状态飞行器背风面的旋涡效应,进而使飞行器低速状态的升力和升阻比均提升10%以上,改善了涡波一体宽速域乘波飞行器的高低速气动性能.     

圆柱尾迹影响旁路转捩末期发卡涡涡包的研究

基于TR-PIV技术, 通过侧视和俯视两种情况对圆柱尾迹影响下旁路转 捩末期发卡涡涡包的结构及特征尺寸进行了实验研究. 结合二维空间子波变换和\lambda _{ci}准则, 运用线性随机估计方法对速度信号进行条件平均. 在侧视情况下, 条件平均结 果显示, 在边界层中一系列发卡涡涡头与壁面构成17^{\circ}的倾角, 并且被尾迹涡所占据的低 速区域出现在涡包上方的主流区中. 在俯视的结果中, 沿流向方向拉伸(流向尺度 3\delta, 展向尺度0.55δ)的低速条带结构出现在法向高 度为y/δ =0.2的流向-展向平面中, 并且在该低速条带的两侧对称地出 现了沿流向分布的反向旋转的涡结构. 可以得出: 在圆柱尾迹影响下旁路转捩的末期, 由于 尾迹涡诱导作用的影响, 发卡涡涡包在形态上显示出了更大尺度的特征.     

Measurements of the aperiodic wake of a hovering rotor

 An experimental investigation was made to study the aperiodic flow characteristics of the tip vortices generated by one-bladed and two-bladed hovering rotors. Measurements of the tip vortex locations and accompanying aperiodicity statistics were established as a function of vortex age. Velocity field measurements were made using three-component laser Doppler velocimetry. The average amplitude of the aperiodicity was found to be a fraction of the measured viscous core radius, this being approximately 5% of blade chord or about 50% of the core radius for wake ages of less than two rotor revolutions. The aperiodicity appeared isotropic. A numerical analysis of the aperiodicity problem based on convolution with an assumed displacement probability function showed that for this experiment the measured tangential velocities in the tip vortices were underestimated by approximately 20% and the viscous core radii were overestimated by 20%. There was no evidence that the number of blades or the blade passage adversely influenced the aperiodicity of the rotor tip vortices. Received: 22 August 1997/Accepted: 4 February 1998     

Lift enhancement of airfoil and tip flow control for wind turbine

Two techniques that improve the aerodynamic performance of wind turbine airfoils are described. The airfoil S809, designed specially for wind turbine blades, and the airfoil FX60-100, having a higher lift-drag ratio, are selected to verify the flow control techniques. The flow deflector, fixed at the leading edge, is employed to control the boundary layer separation on the airfoil at a high angle of attack. The multi-island genetic algorithm is used to optimize the parameters of the flow deflector. The results indicate that the flow deflector can suppress the flow separation, delay the stall, and enhance the lift. The characteristics of the blade tip vortex, the wake vortex, and the surface pressure distributions of the blades are analyzed. The vortex diffuser, set up at the blade tip, is employed to control the blade tip vortex. The results show that the vortex diffuser can increase the total pressure coefficient of the core of the vortex, decrease the strength of the blade tip vortex, lower the noise, and improve the efficiency of the blade.     

旋翼尾流与地面干扰时地面涡现象的研究

用Ｎ－Ｓ方程对近地飞行时旋翼尾流与地面干扰时产生的地面涡现象进行了数值计算旋翼对流场的作用由分布在特定区域内的动量源项模拟结果表明，旋翼尾流撞到地面后的卷起和轴向流动的拉伸作用是形成地面涡的原因；地面边界层形成的二次分离涡向地面涡内输入（与尾流所携带的涡量）相反的涡量，而使地面涡保持平衡；地面涡的存在和运动使旋翼附近流场大大改变     

Effect of mini-flaps on the structure of the near wake behind a model half-wing

The effect of mini-flaps on the vortex structure of the near wake flow behind a model of a half-wing, rectangular in plan, is investigated. In a subsonic wind tunnel the time-average flow parameters are measured in several sections behind a model with flaps mounted on both upper and lower surfaces near the trailing edge. The wake flow parameters are compared with those for a model with no flaps. The considerable effect of the flaps on the flow structure in the viscous core of a tip vortex formed behind the model half-wing is established.     

Rollup region of a turbulent trailing vortex issued from a blade with flow separation

This paper presents the results of an experimental investigation on the near field of a tip vortex generated by a blade at moderate incidence. The experiments were conducted at Re=15 000 and the boundary layer over the blade separated around midchord on the upper surface. Laser-Doppler measurements of the turbulent flow (Tu=1.5%) were performed at various stations downstream of the blade. The three components of the mean velocity field and turbulent attributes were quantified at cross-planes, characterizing both the blade wake and the tip vortex structure. This allowed the analysis of the rollup and initial stages of decay of the tip vortex in the light of known theories and models. The axial velocity defect at the center of the vortex core evolved as x⁻¹ log x, without displaying any significant outgrowth imposed by the separated flow upstream. Momentum balances were also carried out at a station downstream to the conclusion of vortex rollup. The approximate axisymmetry of the flow field in the trailing vortex was used to formulate the balances in a cylindrical coordinate system. Among other observations, it was seen that an adverse axial pressure gradient developed in the vortex core, which reinforced the tenacity of the axial velocity defect. In contrast, an area influenced by a favorable pressure gradient was found outside the core.     

叶轮机械气动噪声的研究进展

从机理研究、数值预测和控制方法3方面对叶轮机械气动噪声的研究进展和现状进行综述.主要内容包括: 离散噪声和宽频噪声的机理研究,离散噪声包括叶轮旋转的自身噪声和动静干涉噪声,宽频噪声包括进气畸变噪声、叶顶间隙流动噪声、尾迹噪声、涡脱落噪声;基于声比拟理论的方法在噪声预测方面的应用;有源控制、叶片尾迹控制、非等距叶片和多孔材料等新型噪声控制技术的综述.最后对叶轮机械气动噪声的研究现状进行了总结并对今后的研究工作进行了展望.      

Recent developments in background oriented Schlieren methods for rotor blade tip vortex measurements

The compressible blade tip vortex of rotary wings has been the subject of numerous investigations and its importance for the understanding of the helicopter flow field has been clearly emphasised. Due to its great impact on the dynamics of the flow field, the investigation of the tip vortex is directly linked to issues of flow control and aeroacoustic optimisation. However, among velocity field data, additional core density information on the blade tip vortex is desirable with a view to vortex modelling. In this work we describe an airborne background oriented Schlieren system for full-scale helicopter flight tests as well as the first results of the tomographic reconstruction of the compressible vortex core. We report the measurements of both a 0.4 Mach-scaled rotor model of the MBB BO 105 and the corresponding full-scale helicopter in hover flight condition. The tomographic reconstruction of the data allows us to estimate the density and the radius for the viscous core.     

Large aerodynamic forces on a sweeping wing at low Reynolds number

The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically. After an initial start from rest, the wing is made to execute an azimuthal rotation (sweeping) at a large angle of attack and constant angular velocity. The Reynolds number (Re) considered in the present note is 480 (Re is based on the mean chord length of the wing and the speed at 60% wing length from the wing root). During the constant-speed sweeping motion, the stall is absent and large and approximately constant lift and drag coefficients can be maintained. The mechanism for the absence of the stall or the maintenance of large aerodynamic force coefficients is as follows. Soon after the initial start, a vortex ring, which consists of the leading-edge vortex (LEV), the starting vortex, and the two wing-tip vortices, is formed in the wake of the wing. During the subsequent motion of the wing, a base-to-tip spanwise flow converts the vorticity in the LEV to the wing tip and the LEV keeps an approximately constant strength. This prevents the LEV from shedding. As a result, the size of the vortex ring increases approximately linearly with time, resulting in an approximately constant time rate of the first moment of vorticity, or approximately constant lift and drag coefficients. The variation of the relative velocity along the wing span causes a pressure gradient along the wingspan. The base-to-tip spanwise flow is mainly maintained by the pressure-gradient force. The project supported by the National Natural Science Foundation of China (10232010)     

Numerical investigation of the effect of winglets on the evolution of an aircraft vortex wake

The effect of winglets on the aerodynamic characteristics of a heavy aircraft and the parameters of the vortex wake behind it is investigated for the landing regime. The solution of the complete problem is obtained by breaking up the wake into three regions, namely, the near, intermediate, and far flowfields, in which the corresponding subproblems are successively solved. The wake flowfields are obtained at different distances from the aircraft, together with the distributions of the mean azimuthal velocity over the vortex radius, and the lifetime of the vortex system is estimated for several one-and two-element wingtip versions. All the results are compared with those for the baseline layout with no winglets.