兆瓦级H型垂直轴风力发电机气动设计方案的数值模拟研究

为解决兆瓦级H型垂直轴风力发电机气动设计过程中实验和数值模拟方面耗费巨大的问题,基于升力线模拟方法完成了兆瓦级H型垂直轴风力发电机的气动设计,并利用该方法研究不同垂直轴风力机翼型设计方案对整机气动性能的影响,研究结果表明:基元翼型选用NACA0015和NACA0018对称翼型能够获得更高的风能利用率;整机叶片造型方案中,前掠翼型性能优于直叶片,前掠翼型方案的最大风能利用率随掠角增大而小幅上升,完整旋转周期内的风能利用率则随掠角增加先增大后减小,且在掠角3°时可取到整体最大风能利用率;后掠翼型性能差于直叶片,风能利用系数随掠角增大而减小;前掠与后掠组合翼型方案性能稍好于直叶片,但不如前掠叶片;不同方案之间存在性能差异的原因可能在于不同翼型的叶片分离涡在竖直方向上的旋涡脱落顺序方面存在差异,其中上部较早脱落的前掠方案有助于风能利用系数提升,下部较早脱落的后掠方案则会对风能利用系数产生负面影响。     

Wind tunnel and numerical study of a small vertical axis wind turbine

This paper presents a combined experimental and computational study into the aerodynamics and performance of a small scale vertical axis wind turbine (VAWT). Wind tunnel tests were carried out to ascertain overall performance of the turbine and two- and three-dimensional unsteady computational fluid dynamics (CFD) models were generated to help understand the aerodynamics of this performance.Wind tunnel performance results are presented for cases of different wind velocity, tip-speed ratio and solidity as well as rotor blade surface finish. It is shown experimentally that the surface roughness on the turbine rotor blades has a significant effect on performance. Below a critical wind speed (Reynolds number of 30,000) the performance of the turbine is degraded by a smooth rotor surface finish but above it, the turbine performance is enhanced by a smooth surface finish. Both two bladed and three bladed rotors were tested and a significant increase in performance coefficient is observed for the higher solidity rotors (three bladed rotors) over most of the operating range. Dynamic stalling behaviour and the resulting large and rapid changes in force coefficients and the rotor torque are shown to be the likely cause of changes to rotor pitch angle that occurred during early testing. This small change in pitch angle caused significant decreases in performance.The performance coefficient predicted by the two dimensional computational model is significantly higher than that of the experimental and the three-dimensional CFD model. The predictions show that the presence of the over tip vortices in the 3D simulations is responsible for producing the large difference in efficiency compared to the 2D predictions. The dynamic behaviour of the over tip vortex as a rotor blade rotates through each revolution is also explored in the paper.     

On the structural behaviour of variable-geometry oval-trajectory Darrieus wind turbines

We developed a computational model based on a finite-element mixed formulation with quadratic isoparametric beam elements. We applied this model to the analysis of a blade-wagon: a novel structure characteristic of an innovative concept in wind-power called VGOT Darrieus turbine. We studied the structural behaviour of its main components: chassis, suspension and blade, using combinations of beam/bar elements in an appropriate assembling. We defined a set of parameters to characterize the structural behaviour which help to understand the contribution of the different components and assist the process of redesign.     

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。     

Design space exploration of gyrocopter‐type airborne wind turbines

This paper presents a multidisciplinary framework for the design and analysis of gyrocopter‐type airborne wind turbines. In this concept, four rotary wings provide lift to a flying vehicle, and excess power is extracted using gearboxes and generators before being transferred to the ground through electrical conductors embedded in a structural tether. A physical breakdown of the system was performed, and five models were constructed: wind model, rotor aerodynamics, structural mass, electrical system, and tether (structures and aerodynamics). A stochastic optimizer in the framework enforces interdisciplinary compatibility and maximizes electrical power transmitted to the ground under various operating conditions. The framework is then used to explore the design space of this advanced concept in numerous flight conditions. The effect of implementing new technologies was also studied in order to evaluate their effect on the overall performance of the system. It is shown through a 1.3MW design that a gyrocopter‐type airborne generator could provide more power than a ground‐based wind turbine for a given blade radius, although only a fraction of the available wind power can be harvested using off‐the‐shelf technologies and components. The work presented in this study demonstrates the challenges of designing a high altitude wind generator and shows that performance is affected by complex interactions between each subsystem. Copyright © 2015 John Wiley & Sons, Ltd.     

PIV measurements and CFD simulation of the performance and flow physics and of a small‐scale vertical axis wind turbine

The aerodynamics generated by a small small‐scale vertical axis wind turbine are illustrated in detail as a NACA0022 rotor blade carries out a complete rotation at three tip speed ratios. These aerodynamic details are then linked to the wind turbine performance. This is achieved by using detailed experimental measurements of performance and near‐blade particle image velocimetry (PIV) and also by using a two‐dimensional Reynolds‐averaged Navier–Stokes‐based computational fluid dynamics (CFD) model. Uniquely, therefore, the CFD model is validated against both PIV visualizations and performance measurements. At low tip speed ratios ( λ = 2), the flow field is dominated by large‐scale stalling behaviour as shown in both the experimental results and simulations. The onset of stall appears to be different between the experiment and simulation, with the simulation showing a gradual separation progressing forward from the trailing edge, while the experiment shows a more sudden leading‐edge roll‐up. Overall, similar scales of vortices are shed at a similar rate in both the experimental results and simulations. The most significant CFD–PIV differences are observed in predicting flow re‐attachment. At a higher tip speed ratio ( λ = 3), the flow separates slightly later than in the previous condition, and as occurs in the lower tip speed ratio, the main differences between the experiment and the simulation are in the flow re‐attachment process, specifically that the simulations predicts a delay in the process. At a tip speed ratio of 4, smaller predicted flow separation in the latter stages of the upwind part of the rotation is the main difference in comparison to the experiment. Copyright © 2013 John Wiley & Sons, Ltd.     

Innovative improvement of a drag wind turbine performance

Drag type wind turbines have strong potential in small and medium power applications due to their simple design. However, a major disadvantage of this design is the noticeable low conversion efficiency. Therefore, more research is required to improve the efficiency of this design. The present work introduces a novel design of a three-rotor Savonius turbine with rotors arranged in a triangular pattern. The performance of the new design is assessed by computational modeling of the flow around the three rotors. The 2D computational model is firstly applied to investigate the performance of a single rotor design to validate the model by comparison with experimental measurements. The model introduced an acceptable accuracy compared to the experimental measurements. The performance of the new design is then investigated using the same model. The results indicated that the new design performance has higher power coefficient compared with single rotor design. The peak power coefficient of the three rotor turbine is 44% higher than that of the single rotor design (relative increase). The improved performance is attributed to the favorable interaction between the rotors which accelerates the flow approaching the downstream rotors and generates higher turning moment in the direction of rotation of each rotor.     

A new dynamic inflow model for vertical‐axis wind turbines

This paper presents a new dynamic inflow model for vertical‐axis wind turbines (VAWTs). The model uses the principle of Duhamel's integral. The indicial function of the inflow‐ and crossflow‐induction required to apply Duhamel's integral is represented by an exponential function depending on the thrust coefficient and the azimuthal position. The parameters of this approximation are calibrated using a free wake vortex model. The model is compared with the results of a vortex model and higher fidelity computational fluid dynamic (CFD) simulations for the response of an actuator cylinder to a step input of the thrust and to a cyclic thrust. It is found that the discrepancies of the dynamic inflow model increase with increasing reduced frequency and baseline thrust. However, the deviations remain small. Analysing the application of a finite‐bladed floating VAWT with non‐uniform loading and validating it against actuator line CFD results that intrinsically include dynamic inflow shows that the new dynamic inflow model significantly outperforms the Larsen and Madsen model (which is the current standard in fully coupled VAWT models) and enhances the modelling of VAWTs.     

风力发电机组的空气气动力特性和发电机的控制

首先研究风力发电机组的空气动力特性,确定风力发电机组的最优工作点以及在各种风速下的控制策略;然后参照风能利用系数的特点确定自寻优控制策略;最后讨论了发电机的两种控制方式,即转速控制方式和力矩控制方式,结合空气动力学确定对双馈电机所采取的控制环节以实现最优工作点跟踪。     

Benefits of collocating vertical‐axis and horizontal‐axis wind turbines in large wind farms

In this study, we address the benefits of a vertically staggered (VS) wind farm, in which vertical‐axis and horizontal‐axis wind turbines are collocated in a large wind farm. The case study consists of 20 small vertical‐axis turbines added around each large horizontal‐axis turbine. Large‐eddy simulation is used to compare power extraction and flow properties of the VS wind farm versus a traditional wind farm with only large turbines. The VS wind farm produces up to 32% more power than the traditional one, and the power extracted by the large turbines alone is increased by 10%, caused by faster wake recovery from enhanced turbulence due to the presence of the small turbines. A theoretical analysis based on a top‐down model is performed and compared with the large‐eddy simulation. The analysis suggests a nonlinear increase of total power extraction with increase of the loading of smaller turbines, with weak sensitivity to various parameters, such as size, and type aspect ratio, and thrust coefficient of the vertical‐axis turbines. We conclude that vertical staggering can be an effective way to increase energy production in existing wind farms. Copyright © 2016 John Wiley & Sons, Ltd.     

Evaluating reduced models of aggregated different doubly fed induction generator wind turbines for transient stabilities studies

For the representation of wind farms in transient stability studies of electrical power systems, reduced models based on aggregating identical wind turbines are commonly used. In the case of a wind farm with different wind turbines coupled to the same grid connection point, it is usual to aggregate identical wind turbines operating in similar conditions into an equivalent one. However, in the existing literature, there are not any references to the aggregation of different wind turbines (same wind turbine technology but different rated power or components) into a single one. This paper presents a comparative study of four reduced models for aggregating different DFIG wind turbines, experiencing different incoming winds, into an equivalent model. The first of them is the classical clustering model, in which each equivalent model experiences an equivalent wind. The other reduced models have the same equivalent generation system but different equivalent mechanical systems. Thus, the second and third ones are compound models with a clustering aggregated mechanical system and individual simplified models, respectively, to approximate the individual mechanical power according to the incoming wind speeds. The fourth is a mixed model that uses an equivalent wind speed, which is applied to an equivalent mechanical system (equivalent rotor and drive train) in order to approximate the mechanical power of the aggregated wind turbines. The equivalent models are validated by means of comparison with the complete model of the wind farm when simulated under wind fluctuations and grid disturbances. Finally, recommendations with regard to the applicability of models are established. Copyright © 2014 John Wiley & Sons, Ltd.     

10MW风力机叶片设计及其在随机风载荷下的响应分析

对大型风力机柔性叶片的设计方法及其在随机风载荷作用下的动态响应与载荷特性进行了研究。根据风力机叶片空气动力学和结构设计理论,将柔性叶片离散为多个刚体,形成一个多体系统。根据多体动力学的建模方法和叶片气动模型,考虑两者的相互作用,建立了柔性叶片的非线性耦合动力学方程并开发了相应的仿真程序。算例分析了叶片在随机风载荷作用下的气弹载荷与随机振动响应,并对稳定风速和紊流风速下的响应结果作了对比分析。     

Experimental investigation of the influence of solidity on the performance and flow field aerodynamics of vertical axis wind turbines at low Reynolds numbers

This paper shows the results of an experimental investigation into the effect of changes in solidity on the performance of a Vertical Axis Wind Turbine. Two VAWT configurations are used, one of solidity σ = 0.26 (chord C = 0.03 m) and the other with σ = 0.34 (C = 0.04 m). The turbine performance coefficient (C_p) was measured over a range of tip speed ratios and Particle Image Velocimetry (PIV) was used to determine the flow field around both turbine configurations.Performance (C_p–λ) curves for the two VAWTs are compared at the same Reynolds numbers to investigate the effects of solidity alone on the performance and aerodynamics of each configuration. The higher solidity (σ = 0.34) VAWT attained a similar maximum C_p but with a narrower C_p–λ curve than the lower solidity VAWT. The performance differences between the two VAWT configurations at two tip speed ratios are explained in detail using PIV around both VAWT rotor blades. This allows the linking of detailed aerodynamics to the performance and it was shown that the generation and shedding of stall vortices started earlier on the lower solidity VAWT than the higher solidity VAWT, thus limiting the rotor efficiency.     

Application of the actuator surface concept to wind turbine rotor aerodynamics

The structure of blade tip vortices is recognized as a key issue in wind turbine aerodynamic modelling by many researchers in the field. In the search for an intermediate model between full Navier–Stokes and blade‐element momentum simulations, this article presents a method using rotating actuator surfaces to model wind turbine aerodynamics. An actuator surface is a simple planar surface, porous to the flow, which is characterized by velocity and pressure discontinuities, whose action on the flow is achieved through an attached system of forces. These discontinuities and forces are determined from blade‐element analysis and the Kutta–Joukowski relation. After implementing this concept in a three‐dimensional CFD (Computational Fluid Dynamics) method, results are produced for the experimental rotors of NREL and TUDelft. The method is validated against both experimental measurements and the predictions of three other numerical models for wind turbine aerodynamic analysis. Qualitative and quantitative comparisons show that the actuator surface concept agrees well with the other numerical models. In addition to rotor aerodynamic analysis, the actuator surface concept can be used in the study of wake aerodynamics, or as the Eulerian flow solver in hybrid methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Simulating dynamic stall in a two‐dimensional vertical‐axis wind turbine: verification and validation with particle image velocimetry data

The implementation of wind energy conversion systems in the built environment has renewed the interest and the research on Vertical Axis Wind Turbines (VAWTs). The VAWT has an inherent unsteady aerodynamic behavior due to the variation of angle of attack and perceived velocity with azimuth angle. The phenomenon of dynamic stall is then an intrinsic effect of the operation at low tip speed ratios, impacting both loads and power. The complexity of the problem and the need for new design approaches for VAWTs for the built environment have driven the authors to focus this research on the CFD modeling of VAWTs on:

• Comparing the results between commonly used turbulence models: Unsteady Reynolds Averaged Navier‐Stokes – URANS (Spalart‐Allmaras and k‐?) and large eddy models (Large Eddy Simulation and Detached Eddy Simulation).
• Verifying the sensitivity of the model to its grid refinement (space and time).
• Evaluating the suitability of using Particle Image Velocimetry (PIV) experimental data for model validation.

The current work investigates the impact of accurately modeling the separated shed wake resulting from dynamic stall, and the importance of validation of the flow field rather than validation with only load data. The structure and magnitude of the wake are validated with PIV results, and it demonstrated that the accuracy of the different models in simulating a correct wake structure has a large impact in loads.     

Dynamic models of wind farms with fixed speed wind turbines

The increasing wind power penetration on power systems requires the development of adequate wind farms models for representing the dynamic behaviour of wind farms on power systems. The behaviour of a wind farm can be represented by a detailed model including the modelling of all wind turbines and the wind farm electrical network. But this detailed model presents a high order model if a wind farm with high number of wind turbines is modelled and therefore the simulation time is long. The development of equivalent wind farm models enables the model order and the computation time to be reduced when the impact of wind farms on power systems is studied. In this paper, equivalent models of wind farms with fixed speed wind turbines are proposed by aggregating wind turbines into an equivalent wind turbine that operates on an equivalent wind farm electrical network. Two equivalent wind turbines have been developed: one for aggregated wind turbines with similar winds, and another for aggregated wind turbines under any incoming wind, even with different incoming winds.The proposed equivalent models provide high accuracy for representing the dynamic response of wind farm on power system simulations with an important reduction of model order and simulation time compare to that of the complete wind farm modelled by the detailed model.     

A Beddoes‐Leishman–type model with an optimization‐based methodology and airfoil shape parameters

Floating offshore wind turbines operate in a highly unsteady environment; thus, many flow transients occur at the blade cross‐sectional level, which affect the rotor aerodynamics. In every rotor aerodynamics modelling technique requiring the blade element theory, the blade cross‐sectional aerodynamics need to be predicted accurately on the basis of the flow conditions. At reduced frequencies of 0.01 and greater, the flow unsteadiness can be considered significant and cannot be treated as quasisteady. Floating offshore wind turbines can be expected to consistently operate in some degree of yaw or pitch, which may result in reduced frequencies greater than 0.01 over most of the blade when operating at rated wind speeds and rotor RPM. The Beddoes‐Leishman model is a comprehensive but complex model for predicting unsteady airfoil aerodynamics, containing 8 dimensionless time constants. In the present study, the Beddoes‐Leishman model was compared with experimental results of 10 different airfoil profiles, each performed under a range of Reynolds numbers, motion frequencies, mean, and amplitudes of angle of attack. An optimization was performed for all time constants in the model, the results of which were used to formulate a simplified model with fewer equations, without any reduction in accuracy. Further, optimizations were performed against the experimental results of each airfoil, and the optimized constants were compared with shape parameters of the airfoils, yielding possible correlations, which were then applied in the simplified Beddoes‐Leishman model to yield improved accuracy, measured as a 5% reduction in accumulated error between experimental and predicted coefficients of lift.     

Optimum aerodynamic design for wind turbine blade with a Rankine vortex wake

This paper presents a model to optimize the distribution of chord and twist angle of horizontal axis wind turbine blades, taking into account the influence of the wake, by using a Rankine vortex. This model is applied to both large and small wind turbines, aiming to improve the aerodynamics of the wind rotor, and particularly useful for the case of wind turbines operating at low tip-speed ratios. The proposed optimization is based on maximizing the power coefficient, coupled with the general relationship between the axial induction factor in the rotor plane and in the wake. The results show an increase in the chord and a slightly decrease in the twist angle distributions as compared to other classical optimization methods, resulting in an improved aerodynamic shape of the blade. An evaluation of the efficiency of wind rotors designed with the proposed model is developed and compared other optimization models in the literature, showing an improvement in the power coefficient of the wind turbine.     

一种升阻复合型垂直轴风力机

提出了一种基于活固叶片的新型升阻复合型垂直轴风力机。分析了这种风力机的空气动力学原理,阐述了其整体结构,设计并制造了一台扫风面积为0.49 m2的样机。在7 m/s的风速下,对其进行了性能测试:当负载扭矩为3.6 Nm时,风力机仍能可靠自启动,其功率系数曲线具有阻力型垂直轴风力机和升力型垂直轴风力机的双重特点;当负载扭矩为1.5 Nm时,其功率系数接近30%。     

Variable geometry wind turbine for performance enhancement,improved survivability and reduced cost of energy

The conceptual design and proof‐of‐concept testing of a furling vertical axis wind turbine, suited to large‐scale offshore deployment, is described. Through the implementation of variable geometry capabilities, extreme storm loads can be reduced, and unsteady flow‐related fatigue loads can be minimized thereby reducing capital (structural) and maintenance costs. Moreover, annual power generation can be optimized in real‐time to account for unsteady wind effects related to weather and siting thus improving efficiency and annual power generation. Copyright © 2014 John Wiley & Sons, Ltd.