基于CFD技术的垂直轴风力机动态尾流特性研究

利用CFD软件对麦克马斯特大学垂直轴风力机进行不同叶尖速比下的数值模拟,计算结果与风洞试验数据吻合良好。近场尾流中,与单叶片的风力机模拟结果比较,上游叶片产生并向下游延伸的旋涡影响下游运行轨道上叶片的升阻力特性,不仅使叶片扭矩输出峰值降低,而且峰值产生的时间延迟。对垂直轴风力机叶片叶梢进行修改,模拟结果显示,叶片扭矩输出峰值不变,但是谷值有所降低,修改后风力机沿风向推力幅值降低明显;远场尾流中,采用风速轮廓线原理,以瑞典的法尔肯贝里市200kW垂直轴风力机为原型,按照真实的空间排布进行数值模拟。模拟结果显示,上游风力机上下两端处产生较为集中的远场尾流,影响下游风力机叶片下半段的气动性能,下游风力机功率输出降低明显。     

Computational analysis of vertical axis wind turbine arrays

Canonical problems involving single, pairs, and arrays of vertical axis wind turbines (VAWTs) are investigated numerically with the objective of understanding the underlying flow structures and their implications on energy production. Experimental studies by Dabiri (J Renew Sustain Energy 3, 2011) suggest that VAWTs demand less stringent spacing requirements than their horizontal axis counterparts and additional benefits may be obtained by optimizing the placement and rotational direction of VAWTs. The flowfield of pairs of co-/counter-rotating VAWTs shows some similarities with pairs of cylinders in terms of wake structure and vortex shedding. When multiple VAWTs are placed in a column, the extent of the wake is seen to spread further downstream, irrespective of the direction of rotation of individual turbines. However, the aerodynamic interference between turbines gives rise to regions of excess momentum between the turbines which lead to significant power augmentations. Studies of VAWTs arranged in multiple columns show that the downstream columns can actually be more efficient than the leading column, a proposition that could lead to radical improvements in wind farm productivity.     

新型升阻混合型垂直轴风力机气动特性研究

考虑S型与H型垂直轴风力机的特点,设计了一种新型升阻混合型垂直轴风力机,采用CFD法计算其启动与气动性能。结果表明,原始H型垂直轴风力机数值结果与试验值在各工况下吻合良好;新型升阻混合型垂直轴风力机不同方位角下的启动力矩均大于原始H型风力机,最小及最大值分别提升232%和83.3%;S型风轮输出功率随叶片重叠比增加而减小,完全重叠时输出功率基本为0;新型升阻混合型垂直轴风力机最大风能利用率为0.298,具有更复杂的流场特性。     

Analogy between a flapping wing and a wind turbine with a vertical axis of revolution

Based on an analysis of available experimental data, the hypothesis about an analogy between a flapping wing and a wind turbine of the Darrieus rotor type is justified. It is demonstrated that the torque on the shaft of the Darrieus rotor is generated by thrust forces acting on the blades in a pulsed flow. A conclusion is drawn that it is necessary to perform aerodynamic calculations of blades on the basis of the nonlinear theory of the wing in an unsteady flow with allowance for the airfoil thickness. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 152–155, March–April, 2009.     

Dynamic stall model for wind turbine airfoils

A model is presented for aerodynamic lift of wind turbine profiles under dynamic stall. The model combines memory delay effects under attached flow with reduced lift due to flow separation under dynamic stall conditions. The model is based on a backbone curve in the form of the static lift as a function of the angle of attack. The static lift is described by two parameters, the lift at fully attached flow and the degree of attachment. A relationship between these parameters and the static lift is available from a thin plate approximation. Assuming the parameters to be known during static conditions, nonstationary effects are included by three mechanisms: a delay of the lift coefficient of fully attached flow via a second-order filter, a delay of the development of separation represented via a first-order filter, and a lift contribution due to leading edge separation also represented via a first-order filter. The latter is likely to occur during active pitch control of vibrations. It is shown that all included effects can be important when considering wind turbine blades. The proposed model is validated against test data from two load cases, one at fully attached flow conditions and one during dynamic stall conditions. The proposed model is compared with five other dynamic stall models including, among others, the Beddoes–Leishman model and the ONERA model. It is demonstrated that the proposed model performs equally well or even better than more complicated models and that the included nonstationary effects are essential for obtaining satisfactory results. Finally, the influence of camber and thickness distribution on the backbone curve are analysed. It is shown that both of these effects are adequately accounted for via the static input data.     

Dynamic study of a wind turbine blade with horizontal axis

The study of the dynamic behavior of a wind turbine with horizontal axis can be undertaken by various methods of analysis. The effects of the change of the aerodynamic flow (in the steady and unsteady cases), the variation of parameters of the cinematic movement (angle of attack, pitch angle and yaw angle) and the definition of subsystems characteristics that makes the wind turbine (blade, nacelle and pylon) allow one to characterize the structural dynamic behavior of the wind turbine. It is therefore necessary to develop these items. Once this is done, the structural dynamic behavior of the system can be improved. The term `improve' means the increase of the life duration by mastering the fatigue effects and the reduction of cost without sacrificing the aerodynamic output. The present study aims to examine the behavior of the blade, which is the main part of the wind turbine in that it that transmits forces to all other parts of the structure. The model is based on the theory of three-dimensional beams, under the assumption of variable sections of the type NACA 4415 airfoil, and takes into account membrane, transversal shear, flexion and free torsion effects. With regards to the aerodynamic loads (the lift, the drag and the pitching moment), a validation has been undertaken by considering experimental data and numerical results obtained by a CFD code (Fluent). The forces are obtained by means of a parametric CAD method interpolation of the aerodynamic poles by Bézier patch under geometrical constraints solved by a Simplex type algorithm. The emphasis is put on dynamic aspects by a complete processing of the dynamic equilibrium equation, applied to the wind turbine blade with horizontal axis.     

Visualization of flow and vortex structure around a swimming loach by dynamic stereoscopic PIV

Loach has a unique swimming style of bending the whole body and staying at the bottom of water. We studied the three-dimensional flow field around and behind the loach using stereoscopic-PIV. We captured flow fields in horizontal and vertical plane, and it seems loach leaves vortex tube arches. From the analysis of body motion and flow field, we propose flow structure with vortex tube arches connected along the loach body. After being released, they are separated and flow away and dissipate. This research article was submitted for the special issue on Animal locomotion: The hydrodynamics of swimming (Vol. 43, No. 5).     

Mathematical modeling of flows in wind turbines with a vertical axis

Flow in the rotors of wind turbines with a vertical axis of the Darrieus-Savonius type and their combinations is considered within the framework of the Navier-Stokes equations, in the two-dimensional formulation. A parametric investigation of the Darrieus rotor characteristics is carried out. For all configurations the dependence of the moment and power coefficients on the specific speed of the rotor is calculated. The possibility of the Darrieus rotor self- starting from the state of rest is investigated. The effect of nonmonotonicmoment variation for the Darrieus-type rotor is studied for the specific speeds of 0.5 to 1. A combined design of the Darrieus-Savonius rotor is considered to solve the problems due to a small moment of the Darrieus rotor during the start.     

Offshore floating wind turbine and its dynamic problems

Green energy sources and ocean wind power are plentiful in deep sea. More and more offshore wind power plants are constructed in the deep water over hundred meters below the surface. While offshore floating wind turbine system is working, wind turbine, floating foundation, and mooring system affect each other with wind, waves, and currents acting on them. Various offshore floating wind turbine systems and the encountered environmental loads are briefly reviewed and discussed. It is difficult and crucial to comprehensively analyze the aerodynamic-hydrodynamic-service system-structure under the coupling effect of offshore floating wind turbine system. The environmental flow field, structure scale, and rational applications of theories and approaches should be well considered in advance.     

Analytical solutions for a single blade in vertical axis turbine motion in two-dimensions

An analytical model for a time dependent two dimensional flow around a moving profile is developed. The model is suitable for fast aerodynamic and aeroelastic coupling calculations. It determines the inviscid pressure distribution in the vicinity of one blade and the force on the blade in arbitrary two dimensional motion. The method is more flexible than previous analysis: it can represent any profile, pitching motion and blade attachment position. The method is based on conformal mapping techniques and Laurent's series decomposition and is faster and more accurate than standard panel methods. A main idea is to directly treat the singularities of the flow in a mapped plane where any geometrical plane is simplified to a circle. The vorticity is assumed to be shed in the form of a continuous vortex sheet near the trailing edge.     

垂直轴自由变偏角水轮机的多体耦合数值求解方法

基于达朗伯原理建立了自由变偏角水轮机结构动力学模型,并结合粘性CFD方法,形成了一种用于分析自由变偏角潮流能水轮机水动力特性的多体耦合数值计算方法.将该方法与试验及非耦合算法进行了对比分析,并研究了自启动、流速变化和负载变化对水轮机性能的影响规律.研究表明:本文建立的数值计算方法能够有效模拟自由变偏角水轮机在各种非定常过程中的运动特性和动力特性.     

Particle image velocimetry （PIV） measurements of tip vortex wake structure of wind turbine

Large-view flow field measurements using the particle image velocimetry (PIV) technique with high resolution CCD cameras on a rotating 1/8 scale blade model of the NREL UAE phase VI wind turbine are conducted in the engineering-oriented Φ3.2 m wind tunnel.The motivation is to establish the database of the initiation and development of the tip vortex to study the flow structure and mechanism of the wind turbine.The results show that the tip vortex first moves inward for a very short period and then moves out...     

风机叶片涂层雨蚀研究

研究了风电叶片在雨水冲击下的失效过程,利用有限元方法建立雨水冲击的数值模型,分析了雨滴的冲击角度、直径、涂层性能等对涂层受力的影响,并对双雨滴及四雨滴耦合模型进行了研究。结果表明:风雨耦合流场中叶片最大载荷在叶尖处,涂层的冲击受力与雨滴冲击角度和雨滴直径的大小呈正相关。低模量涂层能大幅降低涂层受冲击时的拉伸应力,小幅增加其压缩应力。同一平面内的双雨滴耦合时,拉伸应力受影响的范围较大,压缩应力受影响的范围较小。不同高度差下的双雨滴耦合中,随着高度差的增大,材料拉伸和压缩应力都呈现先增后减的趋势,其中压缩应力随高度差的变化幅度明显大于拉伸应力。四雨滴耦合时压缩应力对间距的变化更加敏感。涂层失效的过程主要为:涂层表面拉应力疲劳产生微裂纹;液压渗透引起裂纹扩展,涂层质量减少,表面粗糙度增加;表面小范围破坏后形成的凹面结构促进涂层的失效。