Design Of Wind Turbine Blades Research Articles

Integrated aero-structural optimization design of pre-bend wind turbine blades

In the optimization design of a pre-bend wind turbine blade, there is a coupling relationship between blade aerodynamic shape and structural layup. The evaluation index of a wind turbine blade not only shows on conventional ones, such as Annual energy production (AEP), cost, and quality, but also includes the size of the loads on the hub or tower. Hence, the design of pre-bend wind turbine blades is a true multi-objective engineering task. To make the integrative optimization design of the pre-bend blade, new methods for the blade’s pre-bend profile design and structural analysis for the blade sections were presented, under dangerous working conditions, and considering the fundamental control characteristics of the wind turbine, an integrated aerodynamic-structural design technique for pre-bend blades was developed based on the Multi-objective particle swarm optimization algorithm (MOPSO). By using the optimization method, a three-dimensional Pareto-optimal set, which can satisfy different matching requirements from overall design of a wind turbine, was obtained. The most suitable solution was chosen from the Pareto-optimal set and compared with the original 1.5 MW blade. The results show that the optimized blade have better performance in every aspect, which verifies the feasibility of this new method for the design of pre-bend wind turbine blades.

On the Improvement of Convergence Performance for Integrated Design of Wind Turbine Blade Using a Vector Dominating Multi-objective Evolution Algorithm

A novel multi-objective optimization algorithm incorporating evolution strategies and vector mechanisms, referred as VD-MOEA, is proposed and applied in aerodynamic- structural integrated design of wind turbine blade. In the algorithm, a set of uniformly distributed vectors is constructed to guide population in moving forward to the Pareto front rapidly and maintain population diversity with high efficiency. For example, two- and three- objective designs of 1.5MW wind turbine blade are subsequently carried out for the optimization objectives of maximum annual energy production, minimum blade mass, and minimum extreme root thrust. The results show that the Pareto optimal solutions can be obtained in one single simulation run and uniformly distributed in the objective space, maximally maintaining the population diversity. In comparison to conventional evolution algorithms, VD-MOEA displays dramatic improvement of algorithm performance in both convergence and diversity preservation for handling complex problems of multi-variables, multi-objectives and multi-constraints. This provides a reliable high-performance optimization approach for the aerodynamic-structural integrated design of wind turbine blade.

Aeroelastic Design and LPV Modelling of an Experimental Wind Turbine Blade equipped with Free-floating Flaps

Trailing edge flaps located outboard on wind turbine blades have recently shown considerable potential in the alleviation of turbine lifetime dynamic loads. The concept of the free-floating flap is specifically interesting for wind turbines, on account of its modularity and enhanced control authority. Such a flap is free to rotate about its axis; camberline control of the free-floating flap allows for aeroelastic control of blade loads. This paper describes the design of a scaled wind turbine blade instrumented with free-floating flaps, intended for use in wind tunnel experiments. The nature of the flap introduces a coupled form of flutter due to the aeroelastic coupling of flap rigid-body and blade out-of-plane modes; for maximal control authority it is desired to operate close to the flutter limit. Analytical and numerical methods are used to perform a flutter analysis of the turbine blade. It is shown that the potential flow aeroelastic model can be recast as a continuous-time Linear-Parameter-Varying (LPV) state space model of a low order, for which formal controller design methodologies are readily available.

On the aero-elastic design of the DTU 10MW wind turbine blade for the LIFES50+ wind tunnel scale model

This paper illustrates the aero-elastic optimal design, the realization and the verification of the wind tunnel scale model blades for the DTU 10 MW wind turbine model, within LIFES50+ project. The aerodynamic design was focused on the minimization of the difference, in terms of thrust coefficient, with respect to the full scale reference. From the Selig low Reynolds database airfoils, the SD7032 was chosen for this purpose and a proper constant section wing was tested at DTU red wind tunnel, providing force and distributed pressure coefficients for the design, in the Reynolds range 30-250 E3 and for different angles of attack. The aero-elastic design algorithm was set to define the optimal spanwise thickness over chord ratio (t/c), the chord length and the twist to match the first flapwise scaled natural frequency. An aluminium mould for the carbon fibre was CNC manufactured based on B-Splines CAD definition of the external geometry. Then the wind tunnel tests at Politecnico di Milano confirmed successful design and manufacturing approaches.

Improved B-Spline Skinning Approach for Design of Hawt Blade Mold Surfaces

AbstractThe intricate 3D design of wind turbine blades has caused unwanted problems for blade designers and blade mold manufacturers. For example the cord length variation and twisting of airfoils, change of the airfoil type and the blade pre-bend can introduce major geometric complications. A novel method is suggested to improve 3D modeling of the blade mold surfaces as well as the required parting lines during the design process of the wind turbine blade. In the proposed algorithm, the blade leading edge surface is trimmed by parting lines calculated based on the blade silhouette while keeping G1 continuity of resulting surfaces. The Minimum Variation Surface (MVS) and strain energy fairing criteria approve that blade mold surfaces obtained by the developed method have better fairness compared to the surface created by the well-established design method. All programs are written in MATLAB and the final surfaces are converted into the standard IGES file format which is importable into any commercial CAD/CAM system.

Perturbation methods for the reliability analysis of wind-turbine blade failure due to flutter

A new reliability framework is proposed to study the influence of uncertainty in various system parameters on the onset of coupled-mode flutter for large wind turbine blades. This study is the first comprehensive example of application of reliability analysis to wind turbine blade instability, affected by various sources of uncertainty. The randomness in flow forces, through a random lift coefficient, and in the structural properties is investigated. The probability of flutter is estimated using a recursive search procedure and four reliability models: First Order Reliability Method (FORM), First Order Reliability Method including the effect of unsteadiness in the aeroelastic loads (FORM-C), Second Order Reliability Method (SORM) and Weighted Average Reliability Method (WARM). Flutter probabilities are compared against the results of Monte Carlo simulations. All methods provide accurate probability approximation in regions close to the mean value of the critical flutter speed and flutter frequency. Among the four methods, the WARM provides the closest approximation to the Monte Carlo simulations in all regions of the variables. It is shown that failure probabilities can be found through an iterative procedure, which could be converted to a simplified formula in future standards for the design of wind turbine blades.

A multi-objective optimization for HAWT blades design by considering structural strength

The challenge of wind turbine blade design is to balance the conflict between high capacity and heavy system loads introduced by the large scale rotor. To solve this problem, we present a multi-objective optimization method to maximize the Annual energy production (AEP) and minimize the blade mass. The well-known Blade element momentum (BEM) theory is employed to predict the aerodynamic performance and AEP of the blade. The blade is simplified as a thin Bernoulli beam. The cross section is modelled as a combination of composite layer, shear webs and spar caps typically. The strain of every cross section has been considered as a constraint to minimize the spar cap thickness for minimizing the blade mass. An improved genetic algorithm (NSGA-II) is applied to obtain the Pareto front set. Several solutions of the Pareto set are selected to compare with the reference blade (NREL 5MW blade). Performance of the rotors on design condition is simulated by STAR-CCM+ to verify the results of BEM theory. Optimal results show that the present blade, which is fully superior to the reference blade, can be selected from the Pareto set. The optimization design method can provide a superior blade with an increase by 2.48% of AEP and a reduction by 5.52% of the blade mass. It indicates the present optimization method is effective. Results of numerical simulations show that the spanwise flow would be increased obviously in tip region of the reference blade. The reason is that chord length variation in blade tip affects the flow and causes minor stall. The abrupt change of chord distribution in blade tip should be avoided to reduce the spanwise flow in initial blade design.

ANALYSIS AND OPTIMIZATION OF HORIZONTAL AXIS WIND TURBINE BLADE PROFILE

With new emerging technologies and innovations in energy sector future seems to be bright. But there’s still few years for implementation of those technologies in commercial market. In time there is need to optimize existing technologies and increase their efficiency. Present research is one step towards that goal. This paper analyses and determine the optimum angle of attack at specific wind velocity for horizontal axis wind turbine. Analysis is done by setting wind speed to 10m/s (as this is average wind speed in most open area where wind turbines are placed) and by changing the angle of attack (6, 7, 8, 9 degrees) variation in different properties such as the power output, pressure distribution is determined. Pressure distributions as well as coefficient of lift to coefficient of drag ratio of different the airfoils are visualized and compared. Finite element analysis (FEA) and computational fluid dynamics (CFD) tools are used for analysis of wind turbine. The paper also discusses important parameters in design of wind turbine blade to maximize the efficiency. From the analysis and design optimization of wind turbine blade, it is found out that, at velocity of 10m/s, blade with angle of attack of 8 degree is optimum for harvesting power from wind. Thus, only optimizing blade angle of attack increases power, changing other parameters like material type,

Aeroelastic design of large wind turbine blades considering damage tolerance

Aeroelastic design of large wind turbine blades considering damage tolerance

Structural optimisation of composite wind turbine blade structures with variations of internal geometry configuration

Structural optimisation techniques are frequently used as part of the design process for composite wind turbine blades. Most commonly this is achieved by modifying material placement within a standard structural design; less attention has been paid to the possibility of varying internal geometry to create novel structural configurations. In this work, a series of wind turbine blade designs with differing structural configurations have been created and compared to investigate the effect of allowing various aspects of the internal structural geometry to be varied. The geometry of the structural spar is thoroughly investigated by modifying the width of the spar caps, and the number and location of shear webs including the spanwise starting and ending locations. The location and extent of a trailing edge reinforcement are also considered, along with the material thickness distribution of the spar and trailing edge reinforcement. A series of five parametric 2D finite element models with geometry and materials placement variables were created and incorporated into a genetic optimisation algorithm. This method allows the optimisation process sufficient freedom to generate designs without being constrained by preconceived ideas of how the internal geometry should be configured. The optimum designs had mass reduced relative to the baseline by 3.5–7.4%. Structural analysis of the optimum designs revealed that the active constraint varied greatly between the different designs, and it is therefore recommended that a wider range of loading cases and constraints needs to be accounted for in optimisations that allow the structural geometry to vary compared to those that use a standard geometry.

Probabilistic model for multi-axial dynamic load combinations for wind turbines

The article presents a model describing the joint probability distribution of multiple load components acting on a wind turbine blade cross section. The problem of modelling the probability distribution of load time histories with large periodic components is addressed by dividing the signal into a periodic part and a perturbation term, where each part has a known probability distribution. The proposed model shows good agreement with simulated data under stationary conditions, and a design load envelope based on this model is comparable to the load envelope estimated using the standard procedure for determining contemporaneous loads. Using examples with simulated loads on a 10MW wind turbine, the behavior of the bending moments acting on a blade section is illustrated under different conditions. The loading direction most critical for material failure is determined using a finite-element model of the blade cross section on which load combinations with different directions but with equal probability are applied. By defining a joint probability distribution and return-period contours for multiple load components, the suggested procedure is applicable to different aspects of the design of wind turbine blades, including the possibility for carrying out reliability analysis on an entire cross section.

Aerodynamic and Structural Integrated Optimization Design of Horizontal-Axis Wind Turbine Blades

A procedure based on MATLAB combined with ANSYS is presented and utilized for the aerodynamic and structural integrated optimization design of Horizontal-Axis Wind Turbine (HAWT) blades. Three modules are used for this purpose: an aerodynamic analysis module using the Blade Element Momentum (BEM) theory, a structural analysis module employing the Finite Element Method (FEM) and a multi-objective optimization module utilizing the non-dominated sorting genetic algorithm. The former two provide a sufficiently accurate solution of the aerodynamic and structural performances of the blade; the latter handles the design variables of the optimization problem, namely, the main geometrical shape and structural parameters of the blade, and promotes function optimization. The scope of the procedure is to achieve the best trade-off performances between the maximum Annual Energy Production (AEP) and the minimum blade mass under various design requirements. To prove the efficiency and reliability of the procedure, a commercial 1.5 megawatt (MW) HAWT blade is used as a case study. Compared with the original scheme, the optimization results show great improvements for the overall performance of the blade.

A site-specific design of a fixed-pitch fixed-speed wind turbine blade for energy optimization using surrogate models

This work seeks to add a new approach to optimize a wind turbine blade's performance by implementing a surrogate model using the Kriging function with the chord, twist and the use of 3 different airfoils as design variables for the maximization of the Annual Energy Production. A combination of Genetic Algorithms and the SQP method for Local Search are used to exploit the model. A baseline design of the blade starts with a replica of the Phase VI blade utilized in a NASA-Ames experiment and a MatLab script utilizes the Blade Element Momentum Theory (BEM) for the aerodynamic analysis. Results show a 23% improvement in energy production by using this method.

Wind Tunnel Testing of Airfoils for Wind Turbine Applications

Accurate wind tunnel measurements of the lift and drag of airfoil sections are critical for the design and performance evaluation of wind turbine blades. As blades continue to increase in size, the demand for highly accurate wind tunnel results at progressively larger Reynolds numbers has also increased. Performing these wind tunnel measurements requires precise experimental control, and three challenges for these measurements are model surface quality, pressure tap effects, and model deflections under aerodynamic loading. These challenges were systematically studied in the Virginia Tech Stability Wind Tunnel using a DU96-W-180 airfoil geometry at a chord Reynolds number (Rec) of 3.0 × 106. Naphthalene sublimation showed turbulent wedges caused by surface imperfections; removing these imperfections increased the lift curve slope by 3%. Pressure tap diameter effects were investigated by placing taps of varying size at the same chord location on the airfoil. These measurements showed a steady pressure bias correlated to tap diameter when making measurements in turbulent boundary layers, and naphthalene visualizations showed a turbulent wedge created by pressure taps at the leading edge. Finally, laser distance sensors were used to measure model deflections/rotations under aerodynamic loading, improving upon the traditional angle of attack measurement. Addressing these challenges has improved the accuracy of lift measurements in the Stability Wind Tunnel and emphasized the need for precise experimental controls when performing these types of wind tunnel measurements.

Accuracy of an efficient framework for structural analysis of wind turbine blades

AbstractThis paper presents a novel framework for the structural design and analysis of wind turbine blades and establishes its accuracy. The framework is based on a beam model composed of two parts—a 2D finite element‐based cross‐section analysis tool and a 3D beam finite element model. The cross‐section analysis tool is able to capture the effects stemming from material anisotropy and inhomogeneity for sections of arbitrary geometry. The proposed framework is very efficient and therefore ideally suited for integration within wind turbine aeroelastic design and analysis tools. A number of benchmark examples are presented comparing the results from the proposed beam model to 3D shell and solid finite element models. The examples considered include a square prismatic beam, an entire wind turbine rotor blade and a detailed wind turbine blade cross section. Phenomena at both the blade length scale—deformation and eigenfrequencies—and cross section scale—3D material strain and stress fields—are analyzed. Furthermore, the effect of the different assumptions regarding the boundary conditions is discussed in detail. The benchmark examples show excellent agreement suggesting that the proposed framework is a highly efficient alternative to 3D finite element models for structural analysis of wind turbine blades. Copyright © 2015 John Wiley & Sons, Ltd.

Design of Wind Turbine Blade with Thick Airfoils and Flatback and its Aerodynamic Characteristic

large-scaled blade has posed many problems related to design and production. After introducing the features of blade with thick airfoils and flatback, based on relevant parameters of Huaren 100 kW wind turbine, the paper designed blade with thick airfoils and flatback, introduced blade parameter design, and analyzed the aerodynamic performance of blades using GH bladed software, obtaining the relationship between power output of wind turbine with blade tip speed ratio Cp. Furthermore, it analyzed the aerodynamic performance of original design blades, modified blades and Huaren 100 kW blades, and assessed the aerodynamic performance of modified blade.

Aero-structural design and optimization of a small wind turbine blade

The study develops a methodology for the aero-structural design including consideration of the starting of a small wind turbine blade. To design a fast-starting blade, starting time was combined with output power in an objective function and the blade allowable stress was considered as a constraint. The output power and the starting time were calculated by the blade-element momentum theory and the simple beam theory was employed to compute the stress and deflection along the blade. A genetic algorithm was employed to solve the constrained objective function, finding an optimal blade for which the starting time was small and output power was high while the stress limitation was also met. Considering the hollow cross-sectional model for the structural analysis, the design variables consist of the chord, twist and the shell thickness along the blade. Results showed that a hollow blade expedites the starting at low speeds by decreasing the blade inertia while the resultant stress along the blade does not exceed the allowable stress. By increasing the contribution of the starting time in the objective function, both the external and internal geometry of the blade help the starting and also provide more powerful hollow blades compared to the solid ones.

Multi-dimensional optimization of small wind turbine blades

This paper describes a computer method to allow the design of small wind turbine blades for the multiple objectives of rapid starting, efficient power extraction, low noise, and minimal mass. For the sake of brevity, only the first two and the last objectives are considered in this paper. The optimization aimed to study a range of blade materials, from traditional fibreglass through sustainable alternatives to rapid prototyping plastic. Because starting performance depends on blade inertia, there is a complex interaction between the material properties and the aerodynamics. Example blades of 1.1 m length were designed to match a permanent magnet generator with a rated power of 750 W at 550 rpm. The materials considered were (a) traditional E-glass and polyester resin; (b) flax and polyester resin; (c) a typical rapid prototyping plastic, ABS-M30; and (d) timber. Except for (d), hollow blades were used to reduce the rotor inertia to help minimize starting time. Two airfoils are considered: the 10% thick SG6043 which has excellent lift:drag performance at low Reynolds number and the SD7062 whose extra thickness (14%) has some structural advantages, particularly for the weaker material (c). All blade materials gave feasible designs with material (d) the only one that required a blade shell thickness greater than the specified minimum value of 1% of the blade chord. Generally, the blade chord and twist increased as starting was given greater importance. In all cases, the associated increase in blade inertia was outweighed by the larger aerodynamic torque. Materials (a), (b), and (d) were better suited to the SG6043 airfoil whereas ABS-M30 benefitted from the thicker SD7062 section.

음향방출(AE)을 이용한 풍력 블레이드의 피로손상 평가

In this study, the flap fatigue test of a 48 m long wind turbine blade was performed for 1 million cycles to evaluate the characteristics of acoustic emission signals generated from fatigue damage of the wind blades. As the number of hits and total energy continued to increase during the first 0.6 million cycles, blade damage was constant. The rise-time result showed that the major aspects of damage were initiation and propagation of matrix cracks. In addition, the signal analysis of each channel showed that the most seriously damaged sections were the joint between the skin and spar, 20 m from the connection, and the spot of actual damage was observable by visual inspection. It turned out that the event source location was related to the change in each channel`s total energy. It is expected that these findings will be useful for the optimal design of wind turbine blades.

A study on structural design and analysis of small wind turbine blade with natural fibre(flax) composite

In recent years, there has been a growing interest in the use of naturally sourced fibres for use in composites design and manufacture. In this work, a structural design on 1-kW-class horizontal axis wind turbine blade using natural flax fibre composite is performed. The structural design results of flax/epoxy composite blade are compared with the design results of glass/epoxy composite blade. In order to evaluate the structural design of the composite blade, the structural analysis was performed by the finite element method. Through the structural analyses, it is confirmed that the designed blade using natural composite is acceptable for structural safety, blade tip deflection, structural stability, resonance possibility and weight.