Leading edge erosion of coated wind turbine blades: Review of coating life models

Erosion of the leading edge of wind turbine blades by droplet impingement wear, reduces blade aerodynamic efficiency and power output. Eventually, it compromises the integrity of blade surfaces. Elastomeric coatings are currently used for erosion resistance, yet the life of such coatings cannot be predicted accurately. This review paper gives an overview of experimentally validated erosion model blocks that can be used to predict the life of the leading edge of coated wind turbine blades. From the reviewed work it is concluded that surface fatigue, as nucleating wear mechanism for erosion damage, can explain erosive wear and failure of the coatings. An engineering approach to surface fatigue, using the Palmgren–Miner rule for cumulative damage, allows for the construction of a rain erosion incubation period equation. Coating life was described as a function of the rain intensity, the droplet diameter, the fatigue properties of the coating and the severity of the conditions. It is recommended to focus coating development on reduction of the impact pressure, e.g. by developing surfaces with a low modulus of elasticity; or on enlarging the safe area by: developing coatings with adjustable compressive stresses and hardness, or coatings without defects and impurities.     

Wind turbine blade coating leading edge rain erosion model: Development and validation

This paper applies existing research to develop an analytical surface fatigue model to predict the initiation of leading edge erosion on wind turbine blade coatings due to rainfall. We have used rain erosion whirling arm tests to determine the surface impact fatigue resistance of different coatings used in the field. The analytic model has been validated to predict the initiation of wind turbine leading edge erosion by using a large data base of photos of leading edge erosion observations taken from wind farms in multiple countries, offshore, and onshore. The aerodynamic impact of the erosion has also been modeled and been used to determine the expected sectional efficiency loss of the damaged airfoils. Combining the leading edge erosion forecast model with the efficiency reduction model, we can predict annual energy production loss over time on different sites due to rain‐induced wind turbine blade coating leading edge erosion.     

Toolbox for optimizing anti‐erosion protective coatings of wind turbine blades: Overview of mechanisms and technical solutions

Factors and structural parameters of coatings influencing the efficiency of protective coating systems against rain erosion of wind turbine blades are reviewed. The possibilities to enhance the attenuation of wave energy from droplet impact, increase damping and varying stiffness, creating interfaces for wave reflection, adding reinforcement for wave scattering, and creating additional layers or skeleton‐like reinforcing or wave absorbing structures, are discussed in the paper. Formulas for quantitative estimation of these effects as well as qualitative relationships between the structural parameters of coatings and their performance are presented. Recommendations and promising directions for the improvement of the protective coating systems for rain erosion protection of wind turbine blades are presented.     

Erosion modelling on reconstructed rough surfaces of wind turbine blades

Numerical simulations of rain droplet impacts on real rough surfaces of leading edges of wind turbine blades are presented. The effect of rough blade surface conditions during liquid impacts on the stress distribution in the protective coating is studied. Realistic rough surfaces of wind turbine blades, obtained from 3D reconstruction of real blades with photogrammetry, as well as artificially generated rough surfaces were introduced into finite element models of the droplet/blade coating interaction. Stress distributions in the protective coating with rough and flat surfaces were studied and compared. The results of the simulations suggest that roughness on the surface of the blade leads to increased stresses in the protective coating.     

风力机叶片涂层风沙冲蚀磨损特性的风洞试验研究

传统的挟沙冲蚀试验台与风沙风洞难以构建均匀风沙流场,难以准确反映风力机叶片的风沙磨损特性。因此,在改造的风沙风洞中,通过对风力机叶片平板试样开展涂层冲蚀磨损试验,探究不同冲击速度、冲击角度及有效截面质量流率对风力机叶片涂层材料冲蚀特性的影响规律。试验结果表明：有效颗粒质量流率一定时,在相同冲击速度与冲击时间内,磨损量在冲击角度约为30°时达到最大。小于30°时,磨损量随冲击角度的增大而快速增加,大于30°时磨损量随冲击角度的增大而逐渐降低;磨损量随冲击速度的增大而增大;磨损量随有效颗粒质量流率的增大而呈线性增大趋势;切削磨损量与总磨损量有相同趋势,冲击磨损量随着冲击角度的增大而逐渐增大。     

挟沙风对风力发电机叶片冲蚀磨损的数值研究

风力发电机叶片的风沙冲蚀问题是风电机组耐候性研究的重点之一,该文通过数值模拟的方法,基于1.5 MW的叶片,建立相似模型,研究不同沙尘粒径、不同来流风速和不同叶尖攻角等冲蚀条件对叶片的磨损特性及规律。研究表明：叶片受到的磨蚀率随风速增大而增加,在9 m/s风速时冲蚀分布集中于叶根、叶尖附近,随着风速增大冲蚀由叶根向叶片的中后段移动,且冲蚀效果更显著;随着沙粒粒径增大,叶片磨蚀率逐渐增大,且集中在叶根和叶片中前段;风沙冲蚀角度影响叶片表面的冲蚀分布,角度越大,冲蚀分布的面积越大。     

Leading edge erosion of wind turbines: Effect of solid airborne particles and rain on operational wind farms

Leading edge erosion (LEE) affects almost all wind turbines, reducing their annual energy production and lifetime profitability. This study presents results of an investigation into 18 operational wind farms to assess the validity of the current literature consensus surrounding LEE. Much of the historical research focuses on rain erosion, implying that this is the predominant causal factor. However, this study showed that the impact of excessive airborne particles from seawater aerosols or from adverse local environments such as nearby quarries greatly increases the levels of LEE. Current testing of leading edge protection coatings or tapes is based on a rain erosion resistivity test, which does little to prove its ability to withstand solid particle erosion and may drive coating design in the wrong direction. Furthermore, it was shown that there is little correlation between test results and actual field performance. A method of monitoring the expected level of erosion on an operational wind turbine due to rain erosion is also presented. Finally, the energy losses associated with LEE on an operational wind farm are examined, with the average annual energy production dropping by 1.8% due to medium levels of erosion, with the worst affected turbine experiencing losses of 4.9%.     

Leading edge erosion of wind turbine blades: Multiaxial critical plane fatigue model of coating degradation under random liquid impacts

A computational model of rain erosion of wind turbine blades is presented. The model is based on the transient fluid–solid coupled finite element (FE) analysis of rain droplet/coating interaction and fatigue degradation analysis. The fatigue analysis of the surface degradation is based on multiaxial fatigue model and critical plane theory. The random rain fields are constructed computationally, and the estimated droplet sizes are included in FE model to acquire a library of load histories. Subsequently, the resulted nonproportional multiaxial high cycle fatigue problem is solved to assess the damage and lifetimes of the coatings. The approach can be used to design new coating systems withstanding longer service times.     

挟沙风作用下风力机叶片涂层冲蚀磨损研究进展

随着化石资源的逐渐枯竭,风力发电技术在近几年得到了大力的发展。内蒙古中西部拥有得天独厚的风力资源,但其周边环境恶劣,风中挟带着大量的沙粒对高速旋转下的风机叶片涂层冲蚀磨损严重,导致风电场对叶片的运营维护成本增加。本文对国内外有关涂层材料的冲蚀磨损研究进行了综述,讨论了涂层材料冲蚀磨损过程中各因素对磨损量、应力应变分布规律、磨损机理等的影响,为研究挟沙风对风机叶片涂层冲蚀磨损的过程提供一些思路和展望。     

Quantification of wind turbine energy loss due to leading-edge erosion through infrared-camera imaging,numerical simulations,and assessment against SCADA and meteorological data

Quantification of the performance degradation on the annual energy production (AEP) of a wind farm due to leading-edge (LE) erosion of wind turbine blades is important to design cost-effective maintenance plans and timely blade retrofit. In this work, the effects of LE erosion on horizontal axis wind turbines are quantified using infrared (IR) thermographic imaging of turbine blades, as well as meteorological and SCADA data. The average AEP loss of turbines with LE erosion is estimated from SCADA and meteorological data to be between 3% and 8% of the expected power capture. The impact of LE erosion on the average power capture of the turbines is found to be higher at lower hub-height wind speeds (peak around 50% of the turbine rated wind speed) and at lower turbulence intensity of the incoming wind associated with stable atmospheric conditions. The effect of LE erosion is investigated with IR thermography to identify the laminar to turbulent transition (LTT) position over the airfoils of the turbine blades. Reduction in the laminar flow region of about 85% and 87% on average in the suction and pressure sides, respectively, is observed for the airfoils of the investigated turbines with LE erosion. Using the observed LTT locations over the airfoils and the geometry of the blade, an average AEP loss of about 3.7% is calculated with blade element momentum simulations, which is found to be comparable with the magnitude of AEP loss estimated through the SCADA data.     

Prospective challenges in the experimentation of the rain erosion on the leading edge of wind turbine blades

Developments in the wind industry reveal intricate engineering challenges, one of them being the erosion on the leading edge of the wind turbine blades. In this review work, the main issues for the wind industry in the experimentation with respect to erosion are examined. After a historical and general overview of erosion, this review focuses on the rain erosion on the leading edge of the wind turbine blades giving prominence to (1) the rain simulations, (2) experimental erosion facilities, and (3) variables to characterise erosion. These three factors have to be improved to establish a research field enabling the prediction of erosion behaviour and providing useful information about how the rainfall affects the leading edge of the wind turbine blades. Moreover, these improvements in the experimentation of the erosion would be a first step to understand and predict the erosion damage of the wind turbine blades. Finally, this review work also will help to cope with experimental investigations and results in the rain erosion on the leading edge with a deeper critical thinking for future researchers.     

The effect of a leading edge erosion shield on the aerodynamic performance of a wind turbine blade

Armour EDGE is a novel shield developed to protect the leading edge of wind turbine blades from erosion. The aerodynamic impact on aerofoils of National Renewable Energy Laboratory (NREL) 5MW wind turbine has been investigated using 2D fully turbulent computational fluid dynamics (CFD), with three profiles at critical locations along the blade simulated both with and without the shield to compare aerodynamic performance. Two wind speeds were investigated that reflect regular operating conditions: at rated speed of 11.4 m/s and a below rated speed of 7 m/s. The results showed that the presence of the shield during rated wind speed reduced the drag by as much as 4.5%, where the lift‐to‐drag ratio increased by a maximum of 4%. At the below rated wind speeds, the shield had negligible impact on the performance of all but one National Advisory Committee for Aeronautics (NACA) 64‐618 profile, which resulted in an increase in the drag coefficient of 7%. It was also found that the suction side of the aerofoil is much more sensitive to leading edge protection placement than the pressure side. It was concluded that the erosion shield as a method of leading edge protection, with a gradual transition from shield to blade, will not have a major impact on the aerodynamic performance of a multi‐megawatt wind turbine blade and could slightly increase aerofoil efficiency at high wind speeds.     

超临界汽轮机再热第一级叶片固粒冲蚀特性的数值分析

采用数值方法计算与分析了超临界汽轮机再热第一级的固体颗粒三维运动特性,根据固体颗粒撞击叶片的位置、速度与撞击角以及叶片材料的抗冲蚀性能综合分析了静叶与动叶的冲蚀机理及冲蚀特性,指出静叶吸力面冲蚀是从动叶反弹回来的固粒撞击所引起的。此外,还分析了动静叶轴向间距及机组负荷对反弹至静叶的颗粒数量的影响,结果表明,随着轴向间距的减小和负荷的降低,反弹回静叶的颗粒数量增加。     

风力发电机组叶片故障诊断

风机叶片的裂纹和断裂是导致风机机组事故的重要因素之一,尽早诊断出风机叶片的故障部位与故障程度,对安全生产具有意义重大.本文将叶片振动信号作为研究对象,利用小波分解方法对其进行信号分解,并与时域和频域方法处理结果进行对比分析,得出诊断结论.仿真结果表明：小波分解方法可以更有效的获取故障特征信号,具有较高的故障诊断率.     

Study of ageing of laminates and its effects on wind turbine blade deflection

Some wind turbines have exceeded their nominal design service life and are continuing their operation with periodic inspections and maintenance. In the case of rotor blades, the reliability of the inspection is very limited because of the blade structure that comprises laminates and sandwich structures, which are very difficult to monitor. For this reason, wind farm owners are searching for technologies or approaches that will guarantee a safe operation of their wind turbines after the design life has elapsed. The main objective of this paper was to investigate whether detection of ageing of wind turbine blades using deflection as key parameter is feasible using commercial equipment. The paper is divided in three phases. In phase 1, the effect of ageing on a new UD‐0° glass fibre with high moduli was obtained. Using these results and bibliography data, a theoretical study was performed in phase 2 to determine the magnitude of blade deflection along its lifetime due to material ageing. Finally, in phase 3, in‐field deflection measurements where performed on a wind turbine blade to evaluate the utility and limitations of commercial equipment for the detection of blade ageing. It was concluded that material ageing could result in an increase in blade deflection under self‐weight that can be detected using commercial measurement equipment. These results can be used by wind farm owners in their O&M strategies to monitor blades over time and decide whether they should be repaired or replaced.     

Review of morphing concepts and materials for wind turbine blade applications

With increasing size of wind turbines, new approaches to load control are required to reduce the stresses in blades. Experimental and numerical studies in the fields of helicopter and wind turbine blade research have shown the potential of shape morphing in reducing blade loads. However, because of the large size of modern wind turbine blades, more similarities can be found with wing morphing research than with helicopter blades. Morphing technologies are currently receiving significant interest from the wind turbine community because of their potential high aerodynamic efficiency, simple construction and low weight. However, for actuator forces to be kept low, a compliant structure is needed. This is in apparent contradiction to the requirement for the blade to be load carrying and stiff. This highlights the key challenge for morphing structures in replacing the stiff and strong design of current blades with more compliant structures. Although not comprehensive, this review gives a concise list of the most relevant concepts for morphing structures and materials that achieve compliant shape adaptation for wind turbine blades.Copyright © 2012 John Wiley & Sons, Ltd.     

New vortex‐lift and tangential‐force models for HAWT aerodynamic load prediction

Horizontal axis wind turbines (HAWTs) experience three‐dimensional rotational and unsteady aerodynamic phenomena at the rotor blades sections. These highly unsteady three‐dimensional effects have a dramatic impact on the aerodynamic load distributions on the blades, in particular, when they occur at high angles of attack due to stall delay and dynamic stall. Unfortunately, there is no complete understanding of the flow physics yet at these unsteady 3D flow conditions, and hence, the existing published theoretical models are often incapable of modelling the impact on the turbine response realistically. The purpose of this paper is to provide an insight on the combined influence of the stall delay and dynamic stall on the blade load history of wind turbines in controlled and uncontrolled conditions. New dynamic stall vortex and nonlinear tangential force coefficient modules, which integrally take into account the three dimensional rotational effect, are also proposed in this paper. This module along with the unsteady influence of turbulent wind speed and tower shadow is implemented in a blade element momentum (BEM) model to estimate the aerodynamic loads on a rotating blade more accurately. This work presents an important step to help modelling the combined influence of the stall delay and dynamic stall on the load history of the rotating wind turbine blades which is vital to have lighter turbine blades and improved wind turbine design systems.     

含尘流透平叶片涂层的气动冲蚀行为

从气运冲蚀的角度,对在喷砂型固体颗粒冲蚀试验装置上使用石英砂颗粒和催化剂果粒对长城1号涂层叶片进行了有关涂层冲蚀行为的试验,根据试验结果讨论了冲击速度的冲击角度对涂层冲蚀率的影响;此外,就颗粒的种类、形状和尺寸对涂层冲蚀率的影响进行了探讨。     

Conjugate heat transfer investigation on the cooling performance of air cooled turbine blade with thermal barrier coating

A hot wind tunnel of annular cascade test rig is established for measuring temperature distribution on a real gas turbine blade surface with infrared camera. Besides, conjugate heat transfer numerical simulation is performed to obtain cooling efficiency distribution on both blade substrate surface and coating surface for comparison. The effect of thermal barrier coating on the overall cooling performance for blades is compared under varied mass flow rate of coolant, and spatial difference is also discussed. Results indicate that the cooling efficiency in the leading edge and trailing edge areas of the blade is the lowest. The cooling performance is not only influenced by the internal cooling structures layout inside the blade but also by the flow condition of the mainstream in the external cascade path. Thermal barrier effects of the coating vary at different regions of the blade surface, where higher internal cooling performance exists, more effective the thermal barrier will be, which means the thermal protection effect of coatings is remarkable in these regions. At the designed mass flow ratio condition, the cooling efficiency on the pressure side varies by 0.13 for the coating surface and substrate surface, while this value is 0.09 on the suction side.