Lightning Analysis of Wind Turbines

Over the past several years, the wind energy industry has received scrutiny regarding wind turbine blade (WTB) recycling due to the landfilling of WTBs caused by a lack of industrially viable recycling solutions. The amount of WTBs that will need to be recycled is set to increase in the United States as the deployment of wind energy is expected to rapidly grow to meet the nation’s energy goals by 2035. While significant progress has been made worldwide, it is still unclear which WTB recycling solutions would be the most cost and energy effective within the United States for the existing fleet of wind turbines. To guide researchers and industry with a clear path forward, a range of options for WTB recycling in the United States are modeled through development of baseline scenarios and the use of formal life cycle assessment (LCA). Model data have been collected through literature review, industry engagement, and expert opinion regarding current end of life practices and considerations surrounding equipment, labor, and logistics. A detailed baseline for WTB decommissioning processes has been developed and used to assess alternative approaches, such as on-site shredding to compare the impacts on greenhouse gas (GHG) emissions. The developed LCA model and baseline scenarios for WTB recycling is used to assess the current WTB decommissioning practices in the United States along with emerging recycling pathways, including cement kiln co-processing and pyrolysis. Initial findings indicate that there are different approaches to decommissioning WTBs in the United States, each of which has unique implications for recycling. In light of this finding, additional results from the modeling will be used to better understand decommissioning practices and assist in making educated decisions on recycling pathways for the future. Throughout the analysis, focus was given to where international efforts might differ from the United States. WTB recycling is occurring worldwide, and different countries have different drivers for creating markets for recycled WTB materials. The contrasts and similarities between the United States and other countries offer insight to areas of opportunity that the United States could investigate and areas that can be readily transferred from existing solutions. By modeling and characterizing the current decommissioning practices and potential recycling solutions for the United States, a clearer vision will be created for pathways forward as to how to handle end of life WTBs to enable more efficient and cost-effective opportunities for material recovery from end-of-life WTBs.

Lightning strike is one of the most severe threats to the wind turbine blades and causes huge damage. Mostly wind turbines are struck by lightning when the blades are rotating. The effect of blade rotation on a lightning discharge attachment is unclear. Therefore, a rod electrode was used in a wind turbine lightning discharge test to investigate the difference in lightning triggering ability when blades are rotating and stationary. A standard switching waveform of 250/2500μs was applied to the rod electrode. Lightning discharge tests of a 1:30 scale wind turbine model with 3m air gaps were performed and the discharge process was observed. Three side receptors were used for Lightning protection system (LPS) of wind turbine blade (WTB). Distance between each receptor was 40cm and 1st receptor had 5cm distance from tip of the WTB. Standard switching impulses (negative and positive) were applied to the WTB with different orientations and rotating speed. The experimental results demonstrated that when negative switching impulses were applied to the wind turbine blade, all the lightning discharges hit on the 1st receptor; however, in the case of positive switching impulse, some discharges also hit on the other receptors, blade surface and nacelle of WTB. The attachment points remain same when the blade is stationary or rotating. The analysis revealed that polarity of switching impulse has significant influence on attachment point, and the rotation has little influence during the attachment process. The results can contribute to optimize the design of LPS of wind turbine blade.

The roughness increase on horizontal axis wind turbine (HAWT) blade surface, especially on the leading edge, can lead to an aerodynamic performance degradation of blade and power output loss of HAWT, so roughness sensitivity is an important factor for the HAWT blade design. However, there is no criterion for evaluating roughness sensitivity of blade currently. In this paper, the performance influences of airfoil aerodynamic parameters were analyzed by the blade element momentum (BEM) method and 1.5 MW wind turbine blade. It showed that airfoil lift coefficient was the key parameter to the power output and axial thrust of HAWT. Moreover, the evaluation indicators of roughness sensitivity for the different spanwise airfoils of the pitch-regulated HAWT blade were proposed. Those respectively were the lift-to-drag ratio and lift coefficient without feedback system, the maximum lift-to-drag ratio and design lift coefficient with feedback system for the airfoils at outboard section of blade, and lift coefficient without feedback, maximum lift coefficient with feedback for the airfoils at other sections under the pitch-fixed and variable-speed operation. It is not necessary to consider the roughness when HWAT can be regulated to the rated power output by the pitch-regulated and invariable-speed operation.

Increasing levels of modernization in different countries worldwide have lead to an exponential growth in national energy demand. India with its huge population base had a total grid connected electric power close to 285 GW during 2015 with annual generation of 1106 TWh accounting to a per-capita energy consumption of 746 kWh. The Government of India under its ambitious plan “Power for all” envisages 24 × 7 power supply for the entire domestic and Industrial loads by the year 2022. This power sector initiative also promises the generation through green path by targeting reduction in carbon footprint. The plan has sanctioned funds for production of 190 GW power based on go green initiative of United Nations Organization and a step forward to create a better environment for future generations. The proposed work aims at design of wind-solar hybrid system for light load decentralized applications. The computational tools were used to model and analyze wind turbine (WT) blade structure for low power applications to suit decentralized power generation based on renewable energy. The comparative studies of test aerofoil with standard NACA 0018 aerofoil indicated conformance of the test aerofoil as a profile for WT blades. The test aerofoil has the feature of easier manufacturability as against standard NACA 0018 profile adopted in commercial WT blades. The studies conformed suitability of test profile at specified angle of attack with WT blade structure and hub construction using balsa wood. The choice of balsa wood was based on properties of lighter weight and adequate strength that was supported on the designed tower of tripod type. The designed WT system was for a rated power output of 75 W while operating at an average wind speed of 4.5 m/s. The system developed will be a feasible option for powering households in rural India.

Feasibility study on a strain based deflection monitoring system for wind turbine blades

Wind turbines are known to be the most efficient method of green energy production, and wind turbine blades (WTBs) are known as a key component of the wind turbine system, with a major influence on the efficiency of the entire system. Wind turbine blades have a quite manual production process of composite materials, which induces various types of defects in the blade. Blades are susceptible to the damage developed by complex and irregular loading or even catastrophic collapse and are expensive to maintain. Failure or damage to wind turbine blades not only decreases the lifespan, efficiency, and fault diagnosis capability but also increases safety hazards and maintenance costs. Hence, non-destructive testing (NDT) methods providing surface and subsurface information for the blade are indispensable in the maintenance of wind turbines. Damage detection is a critical part of the inspection methods for failure prevention, maintenance planning, and the sustainability of wind turbine operation. Industry 4.0 technologies provide a framework for deploying smart inspection, one of the key requirements for sustainable wind energy production. The wind energy industry is about to undergo a significant revolution due to the integration of the physical and virtual worlds driven by Industry 4.0. This paper aims to highlight the potential of Industry 4.0 to help exploit smart inspections for sustainable wind energy production. This study is also elaborated by damage categorization and a thorough review of the state-of-the-art non-destructive techniques for surface and sub-surface inspection of wind turbine blades.

This report presents the study of fluid-structure interaction (FSI) of a 5kW horizontal axis wind turbines (HAWT). The motivation of the current investigation is to address the FSI problem of HAWT in the whole flow field analysis with hybrid turbulence model method which is used to find out the flow and structure characteristics of wind turbine in operation under different tip speed ratio (TSR). The target of current work is to obtain detailed information of flow field and structure response simultaneously using the finite element analysis (FEA) method as well as providing new reliable and accurate approach which could be quickly and economically employed in wind turbine FSI problem analysis. In this report, a detailed and comprehensive literature review related to FSI problem of wind turbine has been presented and includes aerodynamic, wind turbine theory, computational fluid dynamic, fluid structure interaction and aeroelastic stability. A 5kW wind turbine is designed according to blade element momentum (BEM) method and a 3D wind turbine modeling is generated in SolidWorks. The 3D wind turbine modeling is imported into FEA software by coupling with the structure domain and the fluid domain to achieve FSI analysis and different TSR are applied to the computational fluid dynamics (CFD) analysis to gain the wind turbine operation information under different scenarios. The simulation results are investigated to reveal the influence of the FSI phenomenon on wind turbine performance. Analysis of wind turbine aeroelastic stability is conducted to prevent blade from experiencing flutter problem. A multiple objective optimization method for wind turbine design including aerodynamic and structure has been developed to improve wind turbine performance. The flow field analysis results showed that the strength of vortex at the tip and root of the blade increases as wind speed increases when wind turbine is under operating conditions. With wind speed of 10m⁄s, most of the flow over the lower surface remains attached and the wind turbine blade was running under design condition. As the wind speed increases, flow separation emerges. When the wind speed increasing to 16m⁄s, the wind turbine blade works under deep stall condition. The wind turbine power coefficient drops continuously from 0.46 to 0.22, as wind speed increased from 10m⁄s to 20m⁄s. The comparison of wind turbine power and torque coefficient under different CFD configuration shows the advantage of whole flow field analysis with hybrid turbulence model. The structural analysis results demonstrated that most of the pressure force acts at a region around the 1⁄4 chord from the leading edge of the blade under operating condition and the displacement of blade tip in flap direction is bigger than those in the other directions. Modal analysis results deduced that flap is the main type of vibration in first and second modes. The difference of natural frequency between single blade and blade rotor becomes larger as vibration order increases. The dynamic performances of wind turbine blade and rotor are totally different and show the whole flow field method is better than the one third domain method. The wind turbine aeroelastic analysis results illustrate that the bending frequency and torsion frequency are around 23.94Hz and 38.46Hz respectively under TSR=4 and both move towards 30Hz under TSR=1.7. When TSR is smaller than 1.7 the wind turbine will experience flutter due to the overlapping of bending and torsion frequencies. The multiple objectives optimization method takes the aerodynamic performance and blade loading into account to gain better design parameter. The comparison between initial and optimal design shows that optimized method could provide higher electrical energy around 1073kW•h per annum under rated wind speed. The optimized wind turbine critical flutter wind speed will increase from initial design speed of 35m/s to 38m/s under optimization design.

A comprehensive review of waste wind turbine blades in China: Current status and resource utilization

Carbon nanotube-based nanocomposites for wind turbine applications

This paper studies the CFD simulation of forward three-dimensional (3-D) horizontal axis wind turbine (HAWT) blades. Using logarithmic grid and Q-criterion to learn the vortex dynamics around the blades at low rotational speed. The computational fluid dynamics (CFD) simulation uses Q-criterion to probe vortices and logarithmic grid to emphasize the micro-gridding effect of the turbulent boundary layer. The visualization & measurement of the simulation results give the coefficient of pressure (Cp). For forward 3-D wind turbine blade, at low rotational speed, the strongly accelerated laminar region surrounds the lower blade, and the decelerated tip blade region coalesce each other give rise to a reverse limiting streamline, eroding the laminar region further until a little is left on the tip of the blade. The "reverse limiting streamline" grows inward radially, the area is narrowing closing to the leading edge of the blade tip. The second side of the rolled-up vortex appears the velocity ratio (Uc/Ulocal) of the second vortices are higher than the main vortex cores. For radius R=1.547 m, U=12 m/s, at 210 RPM, CL and CD values reach a maximum with fully laminar tip conditions. While at 120 RPM, the CL and CD values reach a minimum in the absence of laminar tips. The results show the detailed vortex dynamic pattern surround the blades, give more understanding to design laminar 3-D blade toward a noiseless wind turbine system.

Wind turbine blades are prone to icing under extreme working conditions, which will reduce the efficiency of wind power generation and seriously affect the service life of wind power system. Therefore, the anti-icing problem of wind turbine blades has become one of the hot topics in wind power technology research. It is of great practical significance to develop anti-icing/deicing technology for wind turbine blades for the safe and effective operation of wind power. In this paper, the numerical simulation optimization design for composite material wind turbine blades anti-/deicing component was studied, and the orthogonal optimization method was employed to optimize the parameters of the wind turbine blade to prevent ice formation. The optimization group parameter group is obtained. Through the wind turbine blade temperature distribution simulation, the correctness of the optimization results of the composite material anti-/deicing component was analyzed. The purpose of this paper is to optimize the heat transfer of anti-/deicing component for composite material wind turbine blade, and lay a theoretical and technical foundation for effectively solving the problem of wind turbine blade icing, which proposing a new composite wind turbine blade anti-/deicing scheme.

<div class="section abstract"><div class="htmlview paragraph">Wind energy is clean and renewable source of energy that is an attractive alternative to non-conventional sources of energy. Due to rapid increase in global energy requirements, this form of energy is gaining its share of importance. Unlike nuclear power or tar sand oils, wind energy does not leave a long-term toxic legacy. Using MATLAB algorithms, multi-optimization of wind turbine design can be achieved. Therefore, an aerodynamic mathematical model is developed to obtain the optimal chord length and twist angle distribution along the blade span. Further, a promising generic blade design is used to initialize a detailed structure optimization wherein leading edge panel (LEP), Spar cap, Shear web, Trailing edge panel (TEP) reinforcement are sized using composite laminates so that the blade is according to the intended design standard. Initially blade airfoils are analyzed on 2D platform and then the results are used to construct 3D model of Horizontal Axis Wind Turbine (HAWT) blade. The 3D designing of composite HAWT blade is done by CAD software Solidworks v16.0 through different airfoil for root, primary and tip and optimization of material thickness and overall mass reduction by the use of composite material through optimization of skin thickness of wind turbine is achieved. This paper is focused on the importance of structural design for optimization of HAWT blade. On further analysis, an increase in aerodynamic power generation as well as marked improvements in overall blade deformation and tip deflection characteristics is observed.</div></div>

One of the main global engineering challenges for the wind energy sector is to develop efficient wind turbines with high fatigue life. Large wind turbine blades made out of polymer composites elevate specific stiffness, strength and good fatigue performance. However, large composite structures are prone to defects such as delamination and adhesive failure, which can lead to crack initiation and propagation under cyclic stress. The presented study covers an overview of the manufacturing defects of wind turbine blades, in-service damages and the available inspection techniques that are used to identify defects in wind turbine blades. In this paper, the detection capabilities and performance of visual inspection, acoustic emissions, ultrasonic testing and X-ray inspection have been reviewed. The paper describes the importance of developing quality control guidelines for wind turbine manufacturing sectors based on standard inspection methods.

Application of videometric technique to deformation measurement for large-scale composite wind turbine blade

Over the past 30 years, wind energy has been established as one of the leading forms of renewable energy. As the industry grows so too does the size of the wind turbines themselves – large wind turbines can now generate up to 15 MW. However, with larger turbines comes additional structural challenges to overcome, where one such challenge is erosion along the leading edge of the blade due to water impingement at the higher tip speeds of the blade. Therefore, in this paper, the development of a novel solution for preventing leading edge erosion on wind turbine blades (LEP) is presented. Primarily, this paper describes the experimental testing campaigns that were performed during LEP development. Based on the results from the rain erosion testing of selected materials, their manufacturability and other mechanical properties, thermoplastic polyurethane has been selected as the most suitable material to manufacture the LEP. The LEP component was de-risked through demonstrator testing and then bonded to the leading edge of a full-scale wind turbine blade. Structural (dynamic, static and fatigue mechanical) testing was performed on the blade with no significant damage observed. The next stage of development is operational trials on a wind turbine in marine conditions.