Horizontal Axis Wind Turbine Blade Research Articles

Wavelet transform-based stress-time history editing of horizontal axis wind turbine blades

Full scale blade fatigue testing is required to verify that the horizontal axis wind turbine (HAWT) blades posses the strength and service life specified in the design. Unfortunately, fatigue tests must be run for a long time period, which has led blade testing laboratories to seek ways of accelerating fatigue testing time and reducing the costs of tests. The objective of this article is to develop a novel method called a WT-based fatigue damage part extracting method. Based on wavelet transform (WT), this method extracts fatigue damage parts from the stress-time history and generates the edited stress-time history with shorter time length. Also, this article proposes a concept of applying accumulative power spectral density (AccPSD) to identify fatigue damage events contained in the stress-time history of HAWT blades. Wavelet functions used in this study are Morl, Meyr, Dmey, Mexh and DB30. It has been found that Mexh wavelet with an AccPSD level of 9000 Energy/Hz provides the edited stress-time history having a maximum reduction of 20.77% in length with respect to the original length, whilst fatigue damage per repetition can be retained almost the same as the original one. In addition, an existing method, time correlated fatigue damage (TCFD), is used to validate the effectiveness of a WT-based fatigue damage part extracting method. The results suggest that not only does the WT improve the accuracy of fatigue damage retained, but also it provides a shorter length of the edited stress-time history. To conclude, WT is suggested as an alternative technique in fatigue durability study, especially for the field of wind turbine engineering.

Multi-objective optimisation of horizontal axis wind turbine structure and energy production using aerofoil and blade properties as design variables

The design of wind turbine blades is a true multi-objective engineering task. The aerodynamic effectiveness of the turbine needs to be balanced with the system loads introduced by the rotor. Moreover the problem is not dependent on a single geometric property, but besides other parameters on a combination of aerofoil family and various blade functions. The aim of this paper is therefore to present a tool which can help designers to get a deeper insight into the complexity of the design space and to find a blade design which is likely to have a low cost of energy. For the research we use a Computational Blade Optimisation and Load Deflation Tool (CoBOLDT) to investigate the three extreme point designs obtained from a multi-objective optimisation of turbine thrust, annual energy production as well as mass for a horizontal axis wind turbine blade. The optimisation algorithm utilised is based on Multi-Objective Tabu Search which constitutes the core of CoBOLDT. The methodology is capable to parametrise the spanning aerofoils with two-dimensional Free Form Deformation and blade functions with two tangentially connected cubic splines. After geometry generation we use a panel code to create aerofoil polars and a stationary Blade Element Momentum code to evaluate turbine performance. Finally, the obtained loads are fed into a structural layout module to estimate the mass and stiffness of the current blade by means of a fully stressed design. For the presented test case we chose post optimisation analysis with parallel coordinates to reveal geometrical features of the extreme point designs and to select a compromise design from the Pareto set. The research revealed that a blade with a feasible laminate layout can be obtained, that can increase the energy capture and lower steady state systems loads. The reduced aerofoil camber and an increased L/D-ratio could be identified as the main drivers. This statement could not be made with other tools of the research community before.

Modal Analysis of Wind Turbine Blades Based on ANSYS Modeling

The modal analysis is an approximate method to study the dynamic characteristics of the structure, the modal is the natural vibration characteristics of the structure, each modal has a specific natural frequency, damping ratios and mode shapes. This thesis will take 1.2MW horizontal axis wind turbine blade for example, and use parametric language APDL of ANSYS for directly modeling, then set the basic parameters of the material, mesh and discuss modal analysis, lastly conduct a detailed analysis of the results.

The Analysis of the Aerodynamic Character and Structural Response of Large-Scale Wind Turbine Blades

A process of detailed CFD and structural numerical simulations of the 1.5 MW horizontal axis wind turbine (HAWT) blade is present. The main goal is to help advance the use of computer-aided simulation methods in the field of design and development of HAWT-blades. After an in-depth study of the aerodynamic configuration and materials of the blade, 3-D mapping software is utilized to reconstruct the high fidelity geometry, and then the geometry is imported into CFD and structure finite element analysis (FEA) software for completely simulation calculation. This research process shows that the CFD results compare well with the professional wind turbine design and certification software, GH-Bladed. Also, the modal analysis with finite element method (FEM) predicts well compared with experiment tests on a stationary blade. For extreme wind loads case that by considering a 50-year extreme gust simulated in CFD are unidirectional coupled to the FE-model, the results indicate that the maximum deflection of the blade tip is less than the distance between the blade tip (the point of maximum deflection) and the tower, the material of the blade provides enough resistance to the peak stresses the occur at the conjunction of shear webs and center spar cap. Buckling analysis is also included in the study.

The impact of yaw error on aeroelastic characteristics of a horizontal axis wind turbine blade

Horizontal axis wind turbines operate under yawed conditions for a considerable period of time due to the power control mechanism or sudden changes in the wind direction. This in turn can alter the dynamic characteristics of a turbine blade because the flow over the rotor plane may trigger complicated induced velocity patterns. In this study, an aeroelastic analysis under yawed flow conditions is carried out to investigate the effects of yaw error on the blade behaviors and dynamic stability. A beam model including geometric nonlinearity coupled with unsteady aerodynamics based on a free-vortex wake method with the blade element theory is employed in the present study. The aerodynamic approach for a horizontal axis wind turbine blade under yawed flow conditions is verified through comparison with measurements. It is also shown that the present method gives slightly better results at high yaw angles than does the method previously published in the literature. The dynamic instabilities of a National Renewable Energy Laboratory 5 MW reference wind turbine have subsequently been investigated for various wind speeds and yaw angles. Observations are made that yaw effects induce considerable changes in airloads and blade structural behavior. Also, the aeroelastic damping values for this particular blade under yawed flow conditions can be reduced by up to approximately 33% in the worst case. Therefore, it is concluded that the impacts of yaw misalignments adversely influenced the dynamic aeroelastic stability of the horizontal axis wind turbine blade.

The Performance Test of Three Different Horizontal Axis Wind Turbine (HAWT) Blade Shapes Using Experimental and Numerical Methods

Three different horizontal axis wind turbine (HAWT) blade geometries with the same diameter of 0.72 m using the same NACA4418 airfoil profile have been investigated both experimentally and numerically. The first is an optimum (OPT) blade shape, obtained using improved blade element momentum (BEM) theory. A detailed description of the blade geometry is also given. The second is an untapered and optimum twist (UOT) blade with the same twist distributions as the OPT blade. The third blade is untapered and untwisted (UUT). Wind tunnel experiments were used to measure the power coefficients of these blades, and the results indicate that both the OPT and UOT blades perform with the same maximum power coefficient, Cp = 0.428, but it is located at different tip speed ratio, λ = 4.92 for the OPT blade and λ = 4.32 for the UOT blade. The UUT blade has a maximum power coefficient of Cp = 0.210 at λ = 3.86. After the tests, numerical simulations were performed using a full three-dimensional computational fluid dynamics (CFD) method using the k-ω SST turbulence model. It has been found that CFD predictions reproduce the most accurate model power coefficients. The good agreement between the measured and computed power coefficients of the three models strongly suggest that accurate predictions of HAWT blade performance at full-scale conditions are also possible using the CFD method.

Torsional Stiffness Effects on the Dynamic Stability of a Horizontal Axis Wind Turbine Blade

Aeroelastic instability problems have become an increasingly important issue due to the increased use of larger horizontal axis wind turbines. To maintain these large structures in a stable manner, the blade design process should include studies on the dynamic stability of the wind turbine blade. Therefore, fluid-structure interaction analyses of the large-scaled wind turbine blade were performed with a focus on dynamic stability in this study. A finite element method based on the large deflection beam theory is used for structural analysis considering the geometric nonlinearities. For the stability analysis, a proposed aerodynamic approach based on Greenberg’s extension of Theodorsen’s strip theory and blade element momentum method were employed in conjunction with a structural model. The present methods proved to be valid for estimations of the aerodynamic responses and blade behavior compared with numerical results obtained in the previous studies. Additionally, torsional stiffness effects on the dynamic stability of the wind turbine blade were investigated. It is demonstrated that the damping is considerably influenced by variations of the torsional stiffness. Also, in normal operating conditions, the destabilizing phenomena were observed to occur with low torsional stiffness.

Extracting fatigue damage parts from the stress–time history of horizontal axis wind turbine blades

Horizontal axis wind turbine (HAWT) blades are a critical component of wind turbines. Full-scale blade fatigue testing is required to verify that the blades possess the strength and service life specified in the design. Unfortunately, fatigue tests must be run for a long time period, which has led blade testing laboratories to seek ways of accelerating fatigue testing time and reducing the costs of tests. The objective of this article is to propose a concept of applying accumulative power spectral density (AccPSD) to identify fatigue damage events contained in the stress–time history of HAWT blades. Based on short-time Fourier transform (STFT), a novel method called STFT-based fatigue damage part extracting method has been developed to extract fatigue damage parts from the stress–time history and to generate the edited stress–time history. It has been found that a STFT window size of 256 and an AccPSD level of 9800 Energy/Hz (cutoff level) provides the edited stress–time history having reduction of 15.38% in length with respect to the original length, whilst fatigue damage per repetition can be retained almost the same level as the original fatigue damage. In addition, an existing method, time correlated fatigue damage (TCFD), is used to validate the effectiveness of STFT-based fatigue damage part extracting method. The results suggest that not only does the STFT improve the accuracy of fatigue damage retained, but also it provides a shorter length of the edited stress–time history. To conclude, STFT is suggested as an alternative technique in fatigue durability study, especially for the field of wind turbine engineering.

Unsteady Blade Element-Momentum Method Including Returning Wake Effects

The wind energy research has grown substantially in the past few years, considerably fostered by the pursuit for a clean and sustainable energy source. Improvements on the design methods are increasingly needed. The purpose of this research is to investigate the use of the Loewys lift deficiency function (LDF), also named Returning Wake Model, coupled with a non-stationary Blade Element-Momentum Method (BEM). The LDF simulates the influence of the wake behind the wind turbine on its capacity to generate power. It is expected that this model reduce the dependency of the several empirical parameters necessary in other wake models which are currently used. Aiming to validate the results obtained in this new approach they are compared with those provided by commercial computational software and they have proven to be very consistent. It is concluded that the method is feasible to be used as an efficient design and optimization tool of upwind horizontal axis wind turbine blades.

Optimized linearization of chord and twist angle profiles for fixed-pitch fixed-speed wind turbine blades

The chord and twist angle radial profiles of a fixed-pitch fixed-speed (FPFS) horizontal-axis wind turbine blade are based on a particular design wind speed and design tip speed ratio. Because the tip speed ratio varies with wind speed, the originally optimized chord and twist angle radial profiles for a preliminary blade design through optimum rotor theory do not necessarily provide the highest annual energy production (AEP) for the wind turbine on a specific site with known wind resources. This paper aims to demonstrate a novel optimal blade design method for an FPFS wind turbine through adopting linear radial profiles of the blade chord and twist angle and optimizing the slope of these two lines. The radial profiles of the blade chord and twist angle are linearized on a heuristic basis with fixed values at the blade tip and floating values at the blade root based on the preliminary blade design, and the best solution is determined using the highest AEP for a particular wind speed Weibull distribution as the optimization criteria with constraints of the top limit power output of the wind turbine. The outcomes demonstrate clearly that the proposed blade design optimization method offers a good opportunity for FPFS wind turbine blade design to achieve a better power performance and low manufacturing cost. This approach can be used for any practice of FPFS wind turbine blade design and refurbishment.

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.

Design of 10 kW Horizontal-Axis Wind Turbine (HAWT) Blade and Aerodynamic Investigation Using Numerical Simulation

In this study, a horizontal-axis wind turbine (HAWT) blade with 10,000 Watt power output has been designed by the blade element momentum (BEM) theory and the modified stall model, and the blade aerodynamics are also simulated to investigate its flow structures and aerodynamic characteristics. The design conditions of the turbine blade in order to display the linear distributions of pitch angle in each section include the rated wind speed, design tip speed ratio and design angle of attack that have been set to 10 m/s, 6 and 6°, respectively. The turbine blade geometry was laid out using S822 airfoils and the blade aspect ratio is 8.02 divided into radius of 3 m and chord length of 0.374 m. Next, the improved BEM theory including Viterna- Corrigan stall model, tip-loss factor and stall delay model has been developed for predicting the performance of the designed turbine blade. Finally, the investigations of aerodynamic characteristics for the turbine blade were performed by the numerical simulation. The Reynolds averaged Navier-Stokes (RANS) equatios combined with the Spalart-Allmaras turbulence model that describes the three dimensional steady state flow on the wind turbine blade were solved with the aid of a commerical Computational Fluid Dynamic (CFD) code. A structured grid of approximately 2.4 million cells formulates the computational domain. The simulation results are compared with the improvd BEM theory at rated wind speed of 10 m/s and show that the CFD is a good method on aerodynamic invesigation of a HAWT blade.

Structural Optimization Design of Horizontal-Axis Wind Turbine Blades Using a Particle Swarm Optimization Algorithm and Finite Element Method

This paper presents an optimization method for the structural design of horizontal-axis wind turbine (HAWT) blades based on the particle swarm optimization algorithm (PSO) combined with the finite element method (FEM). The main goal is to create an optimization tool and to demonstrate the potential improvements that could be brought to the structural design of HAWT blades. A multi-criteria constrained optimization design model pursued with respect to minimum mass of the blade is developed. The number and the location of layers in the spar cap and the positions of the shear webs are employed as the design variables, while the strain limit, blade/tower clearance limit and vibration limit are taken into account as the constraint conditions. The optimization of the design of a commercial 1.5 MW HAWT blade is carried out by combining the above method and design model under ultimate (extreme) flap-wise load conditions. The optimization results are described and compared with the original design. It shows that the method used in this study is efficient and produces improved designs.

Resonances of a Forced Mathieu Equation With Reference to Wind Turbine Blades

A horizontal axis wind turbine blade in steady rotation endures cyclic transverse loading due to wind shear, tower shadowing and gravity, and a cyclic gravitational axial loading at the same fundamental frequency. These direct and parametric excitations motivate the consideration of a forced Mathieu equation. This equation with cubic nonlinearity is analyzed for resonances by using the method of multiple scales. Superharmonic and subharmonic resonances occur. The effect of various parameters on the response of the system is demonstrated using the amplitude-frequency curve. The order-two superharmonic resonance persists for the linear system. While the order-two subharmonic response level is dependent on the ratio of parametric excitation and damping, nonlinearity is essential for the order-two subharmonic resonance. Order-three resonances are present in the system as well and, to first order, they are similar to those of the Duffing equation.

피로수명을 고려한 1 MW급 수평축 풍력터빈 복합재 블레이드 설계에 관한 연구

새롭게 제안된 공력 설계 절차와 In-house 프로그램을 이용하여 1 MW급 수평축풍력 터빈 블레이드의 형상을 결정하였고, 기존에 개발된 블레이드의 실험 결과와 본 연구에서 제안한 블레이드와의 비교를 통하여 공력 설계에 대한 타당성을 제시하였다. 블레이드의 구조 설계는 Netting Rule과 Rule of Mixture를 적용하여 설계를 진행하였다. 설계된 블레이드의 구조적 안전성은 상업적 유한요소프로그램인 MSC.NASTRAN을 사용하여 다양한 하중에 따라 선형 정적해석, 변형해석, 좌굴해석, 진동모드해석 등을 수행하였다. 최종적으로 Spera가 제시한 실험식을 적용하여 요구된 피로수명에 대해 타당성을 확인하였다. In this work, 1 MW class horizontal axis wind turbine blade configuration is properly sized and analyzed using the newly proposed aerodynamic design procedure and the in-house code developed by authors, and its design results are verified through comparison with experimental results of previously developed wind turbine blade. The structural design of the wind turbine blade is carried out using a composite materials and the netting and rule of mixture deign methods. The structural safety of the designed blade structure is investigated through the various load cases, stress, deformation, buckling and vibration analyses using the commercial FEM code, MSC.NASTRAN. Finally the required fatigue life is investigated using the modified Spera's experimental equation.

Structural Analysis for the Blades of a Small Horizontal-Axis Wind Turbine

This study discussed the structural analysis of blades of a small horizontal-axis wind turbine (HAWT). The computational fluid dynamics (CFD) is combined with the computational solid mechanics (CSM) into the one-way fluid-solid interaction. The aerodynamic force calculated by CFD is loaded on the structure, and the structural deformation and stress distribution are calculated using CSM. The physical model in the study is a HAWT blade with the rated power output of 500 W, and the material is engineering plastics. The Young's modulus of material is estimated according to the result of blade static load test. The accuracy of structural analysis is verified, and the blades in rated operating state are analyzed for fatigue failure. The blades in no-load running and rotor parked state are analyzed for ultimate strength. The blades of a wind turbine have large length-to-diameter ratio, and the structure approximates to a cantilever. The accuracy of linear analysis is good under a small load. However, as the load increases, the effect of geometric deformation should be considered to improve the precision of analysis. Therefore, the geometrical nonlinearity is used in this study to analyze the structure of blades in three operating states. The results showed that the safety of blades can meet the IEC 61400-2 international standard. In addition, the required safe distance between blades and tower is estimated at 157 mm according to the critical deformation analysis. According to the natural vibration modal analysis, the blades should be prevented from running at the rotating speed of 744 rpm that causes resonance for long.

Wind turbine design through evolutionary algorithms based on surrogate CFD methods

An automatic design environment using evolutionary techniques has been developed for the design of Horizontal Axis Wind Turbine (HAWT) blades taking into account both the aerodynamics and the structural constraints of the blades. This design environment is based on a simple, fast, and robust aerodynamic simulator intended for the prediction of the performance of any turbine blade produced as an intermediate individual of the evolutionary search process. In order to reduce the computational costs, the results obtained by this simple simulator have been corrected through the application of Artificial Neural Network (ANN) based approximations. An additional stress analysis stage has been introduced in order to take into account the structural resistance of the blades as a constraint throughout the optimization process. Results of the simulations obtained using this technique, of the application of the automatic design procedure and of the performance of the wind turbines thus produced are presented. In a first test case the rotor designed through the proposed method is compared to the one obtained analytically for a given air speed. This comparison to an analytical optimum provides a good index in order to evaluate the performance of the method. In a second case the rotor is optimized for a typical wind speed distribution, which is a more realistic scenario where the cost performance of the resulting turbines needs to be evaluated.

Static and Dynamic Characteristics Study of Wind Turbine Blade

Structural analysis of wind turbine blade is a necessary part in the process of blade design. Based on the ANSYS software, the stress and strain distribution analysis of a kind of 1500kW horizontal axis wind turbine blade is carried out at the action of ultimate flapwise loads, the vibration mode shapes of this blade are also analyzed in this paper, thus providing some reference value for the larger-scale wind turbine blade on structural design．

Research on Structural Lay-up Optimum Design of Composite Wind Turbine Blade

According to theoretical calculating result of stress, four different lay-up structures of 1.2MW horizontal axis wind turbine blade, which can effectively endure various loads, are designed primarily. Based on composite laminate theory and finite element method, through analyzing their stress-strain, the optimal lay-up schema is confirmed. The verified analysis of stiffness and strength were performed under extreme load conditions. Numerical analysis results show that the designed blade structure was safe, and the value of stress and strain was low.

Multi-objective structural optimization of a HAWT composite blade based on ultimate limit state analysis

An extensively automated optimization procedure is presented for a horizontal axis wind turbine (HAWT) blade based on ultimate limit state analysis. Two composite materials named glass fiber reinforced plastic (GFRP) and carbon fiber reinforced plastic (CFRP) are applied with a multi-objective of blade cost and total mass. Laminate layer thickness, material type and orientation angle are tailored for the structural performance and subjected to three design constraints which are derived from analysis of ultimate strength, fatigue failure and critical deflection, respectively. Combining FEM analysis and an evolutionary algorithm, the proposed optimization process has dramatically reduced design cost and improved blade performance.