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As an essential ingredient in the blade element momentum theory, the tip loss effect of rotors plays an important role in the prediction of wind turbine performance. Various tip loss corrections based on the Prandtl tip loss function are analysed in the article. Comparisons with measurements and theoretical analyses show that existing tip loss correction models are inconsistent and fail to predict correctly the physical behaviour in the proximity of the tip. A new tip loss correction model is proposed that remedies the inconsistency. Comparisons between numerical and experimental data show that the new model results in much better predictions of the loading in the tip region. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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This paper presents results of a study to investigate the effect of leading edge erosion on the aerodynamic performance of a wind turbine airfoil. The tests were conducted on the DU 96‐W‐180 wind turbine airfoil at three Reynolds numbers between 1 million and 1.85 million, and angles of attack spanning the nominal low drag range of the airfoil. The airfoil was tested with simulated leading edge erosion by varying both the type and severity of the erosion to investigate the loss in performance due to an eroded leading edge. Tests were also run with simulated bugs on the airfoil to assess the impact of insect accretion on airfoil performance. The objective was to develop a baseline understanding of the aerodynamic effects of varying levels of leading edge erosion and to quantify their relative impact on airfoil performance. Results show that leading edge erosion can produce substantial airfoil performance degradation, yielding a large increase in drag coupled with a significant loss in lift near the upper corner of the drag polar, which is key to maximizing wind turbine energy production. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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The actuator line method (ALM) is today widely used to represent wind turbine loadings in computational fluid dynamics (CFD). As opposed to resolving the whole blade geometry, the methodology does not require geometry‐fitted meshes, which makes it fast to apply. In ALM, tabulated airfoil data are used to determine the local blade loadings, which subsequently are projected to the CFD grid using a Gaussian smearing function. To achieve accurate blade loadings at the tip regions of the blades, the width of the projection function needs to be narrower than the local chord lengths, requiring CFD grids that are much finer than what is actually needed in order to resolve the energy containing turbulent structures of the atmospheric boundary layer (ABL). On the other hand, employing large widths of the projection function may result in too large tip loadings. Therefore, the number of grid points required to resolve the blade and the width of the projection function have to be restricted to certain minimum values if unphysical corrections are to be avoided. In this paper, we investigate the cause of the overestimated tip loadings when using coarse CFD grids and, based on this, introduce a simple and physical consistent correction technique to rectify the problem. To validate the new correction, it is first applied on a planar wing where results are compared with the lifting‐line technique. Next, the NREL 5‐MW and Phase VI turbines are employed to test the correction on rotors. Here, the resulting blade loadings are compared with results from the blade‐element momentum (BEM) method. In both cases, it is found that the new correction greatly improves the results for both normal and tangential loads and that it is possible to obtain accurate results even when using a very coarse blade resolution. 相似文献
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Multimegawatt horizontal axis wind turbines often operate in yawed wind transients, in which the resulting periodic loads acting on blades, drive‐train, tower, and foundation adversely impact on fatigue life. Accurately predicting yawed wind turbine aerodynamics and resulting structural loads can be challenging and would require the use of computationally expensive high‐fidelity unsteady Navier‐Stokes computational fluid dynamics. The high computational cost of this approach can be significantly reduced by using a frequency‐domain framework. The paper summarizes the main features of the COSA harmonic balance Navier‐Stokes solver for the analysis of open rotor periodic flows, presents initial validation results on the basis of the analysis of the NREL Phase VI experiment, and it also provides a sample application to the analysis of a multimegawatt turbine in yawed wind. The reported analyses indicate that the harmonic balance solver determines the considered periodic flows from 30 to 50 times faster than the conventional time‐domain approach with negligible accuracy penalty to the latter. 相似文献
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Joukowski introduced in 1912 a helical vortex model to represent the vorticity of a rotor and its wake. For an infinite number of blades but finite tip‐speed ratio, the model consists of a vortex cylinder of longitudinal and tangential vorticity, a root vortex and a bound vortex disk. A superposition of cylinders is used in this paper to model rotors of radially varying circulation. The relations required to form a consistent system of cylinders are derived. The model contains a term which is not accounted for in the standard blade element momentum (BEM) algorithm. This term is identified as the contribution from the pressure drop due to the wake rotation. The BEM algorithm can be corrected to account for this effect. Unlike previous work on the topic, the contribution is derived for a radially varying circulation. A high‐thrust correction is also presented to extend the model. The optimal power coefficient obtained with this model for the constant circulation rotor is assessed and compared with that of existing solutions. Results from prescribed thrust distributions are compared with that of actuator disk simulations. Steady simulations are performed to compare with the BEM algorithm. The model is also applied to compute the velocity field in the entire domain and perform unsteady simulations. Results for an unsteady simulation corresponding to a pitch change of the rotor is used to compare the model with measurements and a BEM code with a dynamic inflow model. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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A vortex system consisting of a bound vortex disk, a root vortex and a vortex cylinder is presented and applied for skewed wake situations. Both the longitudinal and tangential components of vorticity of the cylinder are considered. A subset of this system leads to a model, which is commonly used in Blade Element Momentum method codes for yawed conditions. Here, all the components of the full vortex system are analyzed in view of extending Blade Element Momentum models. The main assumptions of the current study are a constant uniform circulation, an infinite number of blades, an un‐expanding wake shape and a finite tip‐speed ratio. The investigation remains within the context of inviscid potential flow theory. The model is derived for horizontal‐axis rotors in general, but results are presented for wind‐turbine applications. For each vortex element, the velocity components in all directions are computed analytically or semi‐analytically for the entire domain. Simplified engineering models are provided to ease the evaluation of velocities in the rotor plane. The predominant velocity components are assessed. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Christophe Sicot Philippe Devinant Thomas Laverne Stphane Loyer Jacques Hureau 《风能》2006,9(4):361-370
Incident flows on wind turbines are often highly turbulent, because these devices operate in the atmospheric boundary layer and often in the wake of other wind turbines. This article presents experimental investigations of the effects of a high turbulence level on wind turbine aerodynamics. Power and thrust are measured on a horizontal axis wind turbine model in the ‘Lucien Malavard’ wind tunnel. A grid is used to generate three turbulence levels (4·4%, 9% and 12%) with integral length scale of the order of magnitude of the chord length. Experiments show little effect of turbulence on the wind turbine model power and thrust. This can be justified by analysis of the aerodynamic loads along the blade. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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A newly developed technique for determining the angle of attack (AOA) on a rotating blade is used to extract AOAs and airfoil data from measurements obtained during the MEXICO (Model rotor EXperiments in COntrolled conditions) rotor experiment. Detailed surface pressure and Particle Image Velocimetry (PIV) flow fields at different rotor azimuth positions are examined for determining sectional airfoil data. The AOA is derived locally by determining the local circulation on the blade from pressure data and subtracting the induction of the bound circulation from the local velocity. The derived airfoil data are compared to 2D data from wind tunnel experiments and XFOIL computations. The comparison suggests that the rotor is subject to severe 3D effects originating from the geometry of the rotor, and explains why the Blade Element Momentum technique with 2D airfoil data over‐predicts the loading of the rotor. The extraction technique is verified by employing the derived airfoil characteristics as input to computations using the BEM technique and comparing the calculated axial and tangential forces to the measured data. The comparison also demonstrates that the used technique of determining the AOA is a reliable tool to extract airfoil data from experimental data. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Two simple methods for determining the angle of attack (AOA) on a section of a rotor blade are proposed. Both techniques consist of employing the Biot–Savart integral to determine the influence of the bound vorticity on the velocity field. In the first technique, the force distribution along the blade and the velocity at a monitor point in the vicinity of the blade are assumed to be known from experiments or CFD computations. The AOA is determined by subtracting the velocity induced by the bound circulation, determined from the loading, from the velocity at the monitor point. In the second method, the full pressure distribution on the blade is assumed to be known and used to determine the local distribution of circulation along the surface contour of the blade. Using the local distribution of circulation to determine the influence of the bound vorticity enables the velocity monitor points to be located closer to the blade, and thus to determine the AOA with higher accuracy. Data from CFD computations for flows past the Tellus 95 kW wind turbine at different wind speeds are used to test both techniques. Comparisons show that the proposed methods are in good agreement with existing techniques. The advantage of the proposed techniques, as compared with existing techniques, is that they can be used to determine the AOA on rotor blades under general flow conditions (e.g. operations in yaw or with dynamic inflow). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Low order rotor models such as the actuator line method are desirable as an efficient method of computing the large range of operating and environmental conditions, required to design wind and tidal rotors and arrays. However, the integrated thrust and torque predictions for each rotor are dominated by the blade loading on the outboard sections, where three‐dimensional (3D) effects become increasingly significant, and the accuracy of the reduced order methods remains uncertain. To investigate the accuracy of the spanwise blade loading on an individual rotor, actuator line and blade boundary layer resolved computations of the Model Rotor Experiments in Controlled Conditions (MEXICO) rotor are presented. The high fidelity blade‐resolved simulations give good agreement with measured pressure coefficient and particle image velocimetry data. Alternative lift and drag polars are extracted from the 3D simulated flow fields as a function of radial position. These are then used as replacement inputs for the actuator line method. Significant improvement in the accuracy of the actuator line predictions is found when using these 3D extracted polars, compared with using simulated two‐dimensional lift and drag polars with empirical correction applied to the spanwise loading distribution. Additionally, the 3D flow field data is used to derive different axial and tangential spanwise loading corrections for use with the two‐dimensional blade polars. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Blade resolved computations of two different horizontal axis rotors are conducted to investigate the tip loss mechanism experienced by horizontal axis rotors. The tip loss mechanism specifically refers to the effect of the vorticity that is shed from the outboard blade sections, which results in the blade loading dropping off as the tip is approached. In this paper, the shed vorticity is shown to induce a downwash at the rotor plane and spanwise flow accelerations along the blade surfaces. While the downwash reduces the angle of attack of the approach flow, the spanwise flow accelerations lead to additional momentum transport along the blade. This spanwise momentum transport reduces the magnitude and changes the distribution of the static pressure developed on the pressure and suction surfaces of the outboard blade sections. As a result of this modification, the torque producing force drops off faster than the thrust producing force as the tip is approached, resulting in a rotation of the net force vector towards the streamwise direction. This anisotropy must be accounted for by tip flow corrections if the loading on the outboard blade sections is to be computed with sufficient accuracy. In addition, it is also shown that changes in the static pressure distribution cannot be accurately approximated by only modifying the angle of attack of the approach flow, as this would lead to blade loading changes that are inconsistent with the observed behaviour of the lift and drag coefficients on the outboard blade sections. 相似文献
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The vortex system consisting of a bound vortex disk, a root vortex and a vortex cylinder as introduced by Joukowski in 1912 is further studied in this paper. This system can be used for simple modeling of rotors (e.g. wind turbines) with infinite number of blades and finite tip‐speed ratios. For each vortex element, the velocity components in all directions and in the entire domain are computed analytically in a novel approach. In particular, the velocity field from the vortex actuator disk is derived for the first time. The induction from the entire vortex system is studied and is seen to recall results from 1D momentum theory. It is shown that a superposition of concentric cylindrical systems predicts the independence of annuli, which is assumed in blade element theory and stream‐tube analyses. A simple example of application for the estimation of the velocity deficit upstream of a wind turbine is provided. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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叶片作为风能捕获装置,其气动性能决定着风力机的风能利用效率。为有效提升风力机在低风速条件下的风能捕获能力,借鉴飞机在机翼翼尖添加小翼提升气动性能的设计理念,对风力机叶片叶尖添加后掠L型叶尖小翼,并采用标准的k-ε湍流模型对加装小翼叶片和原型叶片在不同风速条件下进行3维流场的数值模拟研究。结果表明：与原型叶片相比,后掠L型叶尖小翼对通过叶尖区域的气流有导流作用,改善了叶尖气流的流动形态,使通过叶尖的气流变得平缓流畅,有效减小了叶尖处的诱导阻力,阻断了叶尖处吸力面的气流分离,减小了叶尖涡;叶尖小翼改变了叶尖区域的压力分布,加大了叶尖部位上下压力面的压差,提升了0.975～0.99倍叶片长度处的叶片转矩,风力机出力变大;加装后掠L型小翼后,风力机的轴向推力增加0.46%～0.81%,增幅较小,而风力机组发电效率提升约3.4%～4.2%,增幅明显。 相似文献
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This paper presents a design tool for optimizing wind turbine blades. The design model is based on an aerodynamic/aero‐elastic code that includes the structural dynamics of the blades and the Blade Element Momentum (BEM) theory. To model the main aero‐elastic behaviour of a real wind turbine, the code employs 11 basic degrees of freedom corresponding to 11 elastic structural equations. In the BEM theory, a refined tip loss correction model is used. The objective of the optimization model is to minimize the cost of energy which is calculated from the annual energy production and the cost of the rotor. The design variables used in the current study are the blade shape parameters, including chord, twist and relative thickness. To validate the implementation of the aerodynamic/aero‐elastic model, the computed aerodynamic results are compared to experimental data for the experimental rotor used in the European Commision‐sponsored project Model Experiments in Controlled Conditions, (MEXICO) and the computed aero‐elastic results are examined against the FLEX code for flow past the Tjæreborg 2 MW rotor. To illustrate the optimization technique, three wind turbine rotors of different sizes (the MEXICO 25 kW experimental rotor, the Tjæreborg 2 MW rotor and the NREL 5 MW virtual rotor) are applied. The results show that the optimization model can reduce the cost of energy of the original rotors, especially for the investigated 2 MW and 5 MW rotors. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Understanding the impact of wave-induced dynamic effects on the aerodynamic performance of Offshore Floating Wind Turbines (OFWTs) is crucial towards developing cost-effective floating wind turbines to harness wind energy in deep water sites. The complexity of the wake of an OFWT has not yet been fully understood. Measurements and numerical simulations are essential. An experiment to investigate the aerodynamics of a model OFWT was undertaken at the University of Malta. Established experimental techniques used to analyse fixed HAWTs were applied and modified for the floating turbine condition. The effects of wave induced motions on the rotor aerodynamic variables were analysed in detail. An open source free-wake vortex code was also used to examine whether certain phenomena observed in the experiments could be reproduced numerically by the lifting line method. Results from hot wire measurements and free-wake vortex simulations have shown that for OFWTs surge-induced torque fluctuations are evident. At high λ a discrepancy in the mean CP between the fixed and floating conditions was found from measurements and numerical simulations. 相似文献
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It is imperative to include three‐dimensional tip flow corrections when using low‐order rotor models that rely on the flow independence principle to compute the blade forces. These corrections aim to account for the effect of pressure equalization at the tips and the accompanying spanwise pressure gradients on the outboard sections, by reducing the computed axial and tangential forces as the blade tips are approached. While Glauert‐type corrections are conventionally employed for actuator disc‐type computations, alternative corrections are required for actuator line computations as they use a finite blade representation. We present actuator line computations of the Model Rotor Experiments in Controlled Conditions (MEXICO) rotor to investigate tip corrections. Using the tip correction factor proposed by Shen et al. (Wind Energy 2005; 8:457–475), the actuator line computations show an improvement in accuracy over similar computations undertaken without a tip correction factor included. Further improvement to the blade loading is achieved by recalibrating the tip correction factor using data extracted from blade resolved computations of the model rotor experiments in controlled conditions rotor. From the rotor resolved computations, the tip loss (reduction in the blade loading on the outboard sections) is found to be more aggressive in the tangential direction than the axial direction. To account for this, we recalibrate the tip correction factor separately in the axial and tangential directions to develop new directionally dependent tip corrections. The resulting actuator line computations show a further improvement in accuracy of the tangential blade loading, resulting in better prediction of the rotor power. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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为在研究大型风力机气动性能的同时考虑其结构动力学特性,基于开源计算流体力学软件OpenFOAM及气动-水动-伺服-控制软件FAST,并结合致动线方法(Actuator Line Method,ALM)实现风力机叶轮周围流场信息与结构响应间的数据交换,最终完成风力机气动-结构仿真平台FASTFOAM构建。通过该平台计算了风场中两台串列布置5 MW风力机的气动性能及结构动力学特性。结果表明:FASTFOAM平台能够快速计算出风力机的功率输出、结构响应及流场信息;风力机尾迹在发展过程中可持续与周围流场进行能量交换而使其速度亏损得以弥补;下游风力机受上游风力机尾迹影响严重,输出功率只有上游风力机的21.05%,且结构动力学响应与上游风力机不同;上游风力机和下游风力机叶轮的主要刺激频率分别为0.16和0.15 Hz。 相似文献