Composite Wind Turbine Blades Research Articles

Modeling and Optimization for the Dynamic Performance of Vertical-Axis Wind Turbine Composite Blades

Abstract This article presents a study of modeling and optimization for the dynamic performance of wind turbine composite material blades and investigates the effects of composite material stacking sequence in addition to some design parameters such as twist angle (ɸ) and aspect ratio (AR) on the whole wind turbine performance. The two-stage Savonius rotor VAWT composite blades are designed and simulated within the solidworks simulation 2020 package. Modified mechanical parameters are introduced to improve the scalability, reliability, and accuracy of the developed models. The lamination plate theory is used to compute the equivalent mechanical properties for each composite blade. The finite element analyses (FEAs) are conducted to investigate the dynamic characteristics (frequency and associated mode shapes) of wind turbine models. Taguchi tools such as analysis of variance (ANOVA), signal-to-noise (S/N) ratio and additive model were employed to evaluate and obtain the significant factors and determine the optimal combination levels of wind turbine design parameters. Mathematical modeling based on response surface methodology (RSM) has been established. The analysis of results shows that the aspect ratio with a contribution of 48.08% had the dominant impact on the rotor performance followed by the stacking sequence and twist angle.

Classical flutter analysis of composite wind turbine blades including compressibility

AbstractFor wind turbine blades with the increased slenderness ratio, flutter instability may occur at lower wind and rotational speeds. For long blades, at the flutter condition, relative velocities at blade sections away from the hub center are usually in the subsonic compressible range. In this study, for the first time for composite wind turbine blades, a frequency domain classical flutter analysis methodology has been presented including the compressibility effect only for the outboard blade sections, which are in the compressible flow regime exceeding Mach 0.3. Flutter analyses have been performed for the baseline blade designed for the 5‐MW wind turbine of NREL. Beam‐blade model has been generated by making analogy with the structural model of the prewisted rotating thin‐walled beam (TWB) and variational asymptotic beam section (VABS) method has been utilized for the calculation of the sectional properties of the blade. To investigate the compressibility effect on the flutter characteristics of the blade, frequency and time domain aeroelastic analyses have been conducted by utilizing unsteady aerodynamics via incompressible and compressible indicial functions. This study shows that with use of compressible indicial functions, the effect of compressibility can be taken into account effectively in the frequency domain aeroelastic stability analysis of long blades whose outboard sections are inevitably in the compressible flow regime at the onset of flutter.

Long-term durability of offshore wind turbine composite blades based on nonlinear load behavior due to pitch movement

This study proposes a fatigue life prediction method for offshore wind turbines consisting of a fatigue load calculation method that accounts for external environmental factors and system interaction, as well as a fatigue stress spectrum calculation method based on the control strategy. First, we conducted an integrated load analysis considering both external environmental factors and system design characteristics to obtain the ultimate load for flapwise, edgewise, and spanwise directions of the blade. We then applied the ultimate load to the blade finite element model to identify the fatigue critical locations (FCLs) of the blade. Subsequently, we calculated force/moment-local stress relationships considering the applied load magnitude and its change in location according to the control strategy. A 10-min wind speed history was applied to these stress relationships to obtain the unit fatigue stress spectrum at the FCLs. This was then combined with the fatigue resistance of the material to obtain the unit fatigue damage at the FCLs. Finally, we applied the statistical wind speed data at a specific site to the unit fatigue damage to calculate the fatigue damage and life. Based on these results, we evaluated the effect of the loads in each blade direction on the fatigue life of a composite blade.

Structural integrity analysis and damage assessment of a long composite wind turbine blade under extreme loading

The high demand of low cost wind energy needs to design large scale turbine blades with reduced weight which poses great challenges to their structural integrity while prone to extreme wind gusts. The loading can cause large-deflection bending and damage leading to significant drop in the load-bearing ability of long composite wind turbine (WT) blades. In this study, a comprehensive finite element (FE) modelling procedure is developed to simulate structural integrity and damage in composite blade using ANSYS software. The three-dimensional blade model is analyzed by carrying out geometrically nonlinear FE analysis to investigate the blade deformation and highly stressed regions leading to possible failure modes. The results show that the blade suction side is subjected to high compressive stress causing local skin buckling, which is further investigated using linear buckling analysis. Such local buckling drives interfacial debonding between skin and spar joined with a weak adhesive. Subsequently, the interfacial damage in the identified critical region is modelled by developing a damage submodel employing cohesive zone model (CZM) approach at the skin-spar interface. The analysis results indicate that buckling driven skin-spar debonding at adhesive interface is initial damage mode which can lead to progressive failure of the blade structure. Consequently, the ultimate load bearing capacity of WT blade is governed by a coupled buckling and debonding phenomenon even at load level below the ultimate design load. The simulation methodology adopted in this study can be employed to develop reliable and cost-effective computational tools for analyzing structural integrity and assessing damage in blade structure than expensive experimental testing.

Lifetime Prediction of Wind Turbine Blade Based on Full-Scale Fatigue Testing

In order to predict the lifetime of products appropriately with long lifetime and high reliability, the accelerated degradation testing (ADT) has been proposed. Composite wind turbine blade is one of the most important components in wind turbine system. Its fatigue cycle is very long in practice. A full-scale fatigue testing is usually used to verify the design of a new blade. In general, the full-scale fatigue testing of blade is accelerated on the basis of the damage equivalent principle. During the full-scale fatigue testing, blade is subjected to higher testing load than normal operating conditions; consequently, the performance degradation of the blade is hastened over time. The full-scale fatigue testing of blade is regarded as a special ADT. According to the fatigue failure criterion, we choose blade stiffness as the characteristic quantity of the blade performance, and propose an accelerated model (AM) for blade on the basis of the theories of ADT. Then, degradation path of the blade stiffness is modeled by using Gamma process. Finally, the lifetime prediction of full-scale megawatt (MW) blade is conducted by combining the proposed AM and blade stiffness degradation model. The prediction results prove the reasonability and validity of this study. This can supply a new approach to predict the lifetime of the full-scale MW blade.

An optimization method based on the evolutionary and topology approaches to reduce the mass of composite wind turbine blades

The design of large and lightweight wind turbines is a current challenge in the wind energy industry. In this context, this work aims to present a novel methodology to reduce the mass of composite wind turbine blades by combining evolutionary and topology optimization schemes in a staggered mode. First, the optimal laminate layout in the outer shell skin of the blade is determined by using genetic algorithms and by assuming that the shear webs are fully dense. Considering this optimized shell skin, the material is removed from the shear webs by using topology optimization. In both cases, the blade is assumed to be subjected to an extreme load scenario, with constraints on the tip displacement, the stresses, the natural vibration frequencies, and buckling phenomena. As an extra feature, the methodology integrates the inverse finite element method to recover the aerodynamically efficient shape of the blade when it is working in normal load scenario as well as to increase the tower clearance safety margin under the extreme load scenario. To illustrate the performance of the methodology, the design of a 28.5-m composite blade is presented. Results show mass savings of up to 23% and a significant increase of the tower clearance safety margin. Furthermore, it is observed that after the classical genetic optimization of the shell skin, there is still margin to achieve additional mass savings via topology optimization of the shear webs without compromising the structural response of the blade.

Fractographic analysis of sandwich panels in a composite wind turbine blade using optical microscopy and X-ray computed tomography

This study provides a new perspective on the failure of sandwich panels in a composite wind turbine blade. Fractographic characteristics of fracture regions are examined thoroughly using optical microscopy and X-ray computed tomography. The detailed fractographic analysis leads to the identification of the failure modes and failure sequence. This study addresses an important but rarely studied failure process in the sandwich panels cored with grooved foams. The partially resin-filled grooves lead to large voids in the foams that cause crack migration of skin/core debonding from one side of sandwich panels to the other. In this study, the adverse effects of the partially resin-filled foams are addressed and the associated challenges in the blade design are highlighted. It is found that the fracture of skin laminates under biaxial compression is characterized by a shear-dominated failure mode in the form of kink bands in two directions. The whitening of skin laminates under tension is caused by micro-cracks in the matrix and the fiber/matrix interface. Moreover, fiber breakage also occurs in the whitening region although it is not visually apparent. These fractographic characteristics could help the identification of the root causes of blade failure if similar observations are found.

Numerical investigation of rain droplet impact on offshore wind turbine blades under different rainfall conditions: A parametric study

The leading edge of a fiber composite wind turbine blade (WTB) is prone to erosion damages due to repeated rain droplet impact during its service life. Such damages are critical to the blade’s aerodynamic as well as structural performance, ultimately resulting in substantial repair costs. An effective design of a coating material for WTB is necessary and its analysis must include variables associated with erosive rain droplets such as (1) droplet diameter, (2) impact velocity, and (3) droplet impact angle. The present paper develops and validates a coupled fluid structure interaction (FSI) computational model for simulating rain droplet impact on WTBs, where the structure domain is modelled using conventional finite element method (FEM) and the fluid domain is modelled using smooth particle hydrodynamics (SPH). The 3D numerical model, developed in LS-DYNA, is validated with published experimental results. Further, a parametric study is considered to understand the effects of varying droplet size, impact angles and impact velocities on the impact responses of the leading edge coating system subjected to different rainfall conditions. The rainfall conditions considered for the analysis correspond to four different rainfall intensities (I) – light rainfall (2mm/hr), moderate rainfall (10mm/hr), heavy rainfall (25mm/hr), and very heavy rainfall (50mm/hr). The results show that the impact responses on the coating system increase with increasing droplet size and increasing droplet impact angle with maximum impulses, stresses and damages developed for normal impingement (90°). Also, the effects of droplet impact angles in the range of 50° to 90° are found critical for rainfall intensities representing very heavy rainfall conditions (I>25mm/hr). The results of the peak contact forces and impulses for the above combination of variables used in the numerical study are found in satisfactory agreement with analytical formulations developed through published experiments. Finally, repetitive rain droplet impact analyses are considered and number of impacts required for onset of erosion damages are found to increase by more than seven times upon reducing impact velocities from 140 m/s to 80 m/s for very heavy rainfall conditions (I>25mm/hr). The present study is expected to deliver a validated numerical model that can contribute towards enhancing the erosive capacity of a WTB.

Mapping Raindrop Erosion of GFRP Composite Wind Turbine Blade Materials: Perspectives on Degradation Effects in Offshore and Acid Rain Environmental Conditions

Abstract Climate change is rapidly forcing the world to create renewable energy that is capable of sustaining future energy requirements globally. The generation of renewable energy at a comparatively lower cost is a major challenge for this industry. Unforeseen weather conditions and environments such as offshore conditions or involving acid rain have a significant effect on the degradation of structural materials of renewable energy devices. For the investigation of droplet erosion behavior of the advanced material for the wind turbine blades, experimental work was carried out on a glass fiber-reinforced epoxy (GFRE) composite in different environments. A whirling arm rig was used for this experimental work in a laboratory-simulated rainfall conditions at a constant tip speed of the rotor blade. Three types of rainwater were used for a range of angles of attack from 15 to 90 deg in an increment of 15 deg. Erosive wear maps have been constructed to show the weather, location, environment, and raindrop erosion effects on the degradation of the wind turbine blade material. This map predicts that erosion in saline and acidic rain conditions acts synergistically on the blade material, which results in delamination between the fiber layers, pit formation, and development of micro stresses leading to loss of adhesion of reinforcement fibers.

Design of a composite wind turbine blade manufactured with the ONE SHOT BLADE® technology

In this work, the design steps of a 10-meter long fiberglass wind turbine blade are introduced. When designing the blade, the innovative manufacturing technology, named ONE SHOT BLADE® technology, able to produce wind turbine blades in “one-piece”, has been taken into account. Critical deflection analyses, considering the most severe loading condition, such as the flapwise bending moment on pressure side, have been performed to verify that the structure complies with the international small wind turbine blade design regulations.

New investigation of mechanical properties of a horizontal axis wind turbine blade based on a hybrid composites with kenaf fibers

The present work aims to assess the benefit of introducing simultaneously kenaf and carbon fibers in a composite wind turbine blade made initially of epoxy glass fiber. After an in-depth analysis of the optimal design of the blade using the Blade Element Momentum theory, an algorithm is generated in order to, firstly, establish the foundation of the blade geometry and secondly, to make a conservative static loading estimation representing a 50-years extreme gust. After performing the blade geometry on the 3D-modeler CATIA® V5, it was imported to PATRAN® software in order to create the mesh of the turbine blade. By modifying the way of stacking layups at each zone of the blade and by taking into account the plies properties, seven models were created. A further comparison was made between these models with a view of finding the best combination of fibers to satisfy the allowable thresholds. After several attempts of fibers combinations, it was finally revealed that the best way to combine the three fibers consists of replacing all unidirectional glass fibers of the blade skin with kenaf fibers and substituting those of the spar cap with carbon fibers while maintaining intact the remaining blade layups.

Design optimization of composite wind turbine blades considering tortuous lightning strike and non-proportional multi-axial fatigue damage

This article presents a design optimization framework which integrates realistic lightning strike electrostatic and fatigue analyses for designing reliable and economical composite wind turbine blades. The novel aspects of this work include: a parametric tortuous lightning stepped leader model that reflects one of the true natural characteristics of the lightning phenomenon; and characterization of both the lightning strike dielectric breakdown failure and multi-axial fatigue failure mechanisms for structural design of composite wind turbine blades. A case study of the structural design optimization of a 5 MW composite wind turbine blade is tested using the framework with two optimization solvers: sequential quadratic programming (SQP) and Bayesian optimization (BO). SQP produces a superior optimal design to BO. In the optimum blade design based on the SQP algorithm, the lightning safety ratio increased by 32% and the expected fatigue life increased more than 15 times compared with the initial blade design.

Study on Air Bubble Defect Evolution in Wind Turbine Blade by Infrared Imaging with Rheological Theory

Air bubble is a manufacturing defect that is common to composite wind turbine blades, which might evolve into cracks, leading to failure under load. The evolution and critical state of air bubble are studied to establish a condition assessment method for blade quality control. A method that is based on rheological theory is proposed to recognize the critical state by temperature jump. The air bubble is regarded as a null set and the temperature distribution of bubble defect is affected by the volumetric strain energy under tensile load. An infrared camera can detect a temperature jump when mechanical characteristics drastically change due to crack formation. A tensile fatigue test was carried out to verify the accuracy of this method. The relative error between the measured and calculated temperature rise at the critical moment was less than 7%. Additionally, the specimen with [0/90]s ply angles is more favorable to maintain the structural stability than the others. The method in this paper establishes a quantitative relationship between the meso-defect and macro mechanical properties. The defect severity of wind turbine blade can be defined by infrared imaging technology.

Damage mode identification of composite wind turbine blade under accelerated fatigue loads using acoustic emission and machine learning

This article studies experimentally the damage behaviors of a 59.5-m-long composite wind turbine blade under accelerated fatigue loads using acoustic emission technique. First, the spectral analysis using the fast Fourier transform is used to study the components of acoustic emission signals. Then, three important objectives including the attenuation behaviors of acoustic emission waves, the arrangement of sensors as well as the detection and positioning of defect sources in the composite blade by developing the time-difference method among different acoustic emission sensors are successfully reached. Furthermore, the clustering analysis using the bisecting K-means method is performed to identify different damage modes for acoustic emission signal sources. This work provides a theoretical and technique support for safety precaution and maintaining of in-service blades.

Fatigue Life of Megawatt-Scale Composite Wind Turbine Blades with Shallow-Angled Laminates

The fatigue life of megawatt-scale composite wind turbine blades implemented with shallow-angled laminates is investigated. Full dynamic simulations of a 5-MW 3-bladed horizontal-axis wind turbine were carried out to estimate the incident fatigue loads. The fatigue stress histories experienced by lay up materials were then computed using a finite-element model of the composite blade developed to ply-level details. Thereafter, the fatigue life of blade was estimated considering the 100% availability of the turbine for the site-specific annual wind distribution related to the wind turbine class IB. It is demonstrated that the application of shallow-angled laminates leads to a more durable design.

Effects of different material failures and surface contact on structural response of trailing edge sections in composite wind turbine blades

This paper presents a detailed numerical study on the structural response of a trailing edge segment from a composite wind turbine blade. The focus is placed on the effects of different material failures and surface contact, some of which are often not modeled in the conventional blade design, on the load-carrying capacity and the failure response of the trailing edge section subject to compressive loading. An advanced nonlinear Finite Element (FE) model capable of predicting different material failures and contact nonlinearities is used to facilitate parametric studies. Furthermore, we propose a possible method to improve the load-carrying capacity of the trailing edge section by structural reinforcement. The strengthening mechanism increases the buckling resistance of the trailing edge section almost to the level where the structure would fail due to the failure of composite materials, thereby utilizing the full strength of composites in the structure.

Manufacturing of Advanced Composite Wind Turbine Blades for Counter Rotating Vertical Wind Turbine

The paper presents the manufacturing process of advanced composite wind turbine blades designed for an experimental counter rotating vertical wind turbine (CR-VAWT). An iterative approach was used to present the manufacturing process of turbine blades starting from presentation of the turbine structure and material description as well as all manufacturing process stages. Two types of turbine blades were successfully manufactured using metallic molds and a cost-effective manufacturing technology. Based on the turbine blades obtained it can be said that the selected manufacturing process showed good results, very similar with results expected in case of using advanced technologies (i.e. autoclave technology.

Fluid flow analysis of composite material-based wind turbine blades using Ansys

The environment-friendly energies are wind, solar, wave and marine current power. In the recent period, the researchers moved to computer simulation from the experimental and numerical analysis. The purpose is to tackle design problems through the optimisation of the present technology and improvement in the efficiency of the wind turbines for long-term sustainability. Therefore, the present research analyses the performance of the wind turbine blade with aerodynamic and structural integrity challenges. Computational fluid dynamics (CFD) is a very powerful tool to solve a wide range of industrial and non-industrial fluid flow problems. CFD, as a promising technique in the wind engineering research, has attracted growing interest in the past two decades. Compared with the conventional experimental approaches, CFD could provide more details about flow field without any need for complicated control and measurement systems. It also provides an inexpensive solution to performing systematic analyses, such as the parametric studies required for performance optimisation of wind turbine blades. Ansys Fluent CFD computer simulation tool has high potentials to determine the effectiveness of air foils and efficiency of turbine blades. This tool provides a qualitative and quantitative prediction with confidence in impact of fluid flow over the wind turbine blade.

Fusion joining of thermoplastic composite wind turbine blades: Lap-shear bond characterization

Wind turbine blades are typically manufactured from a small number of components which are bonded together with an adhesive. Over the life span of a wind turbine, the static and fatigue loads in varying environmental conditions can lead to cracking and/or debonding of the adhesive joints, ultimately leading to blade structural collapse. The objective of this work is to investigate fusion joining of wind turbine blades manufactured using thermoplastic resin. Thermoplastic resins for wind turbine blades can reduce cycle times and energy consumption during manufacturing and facilitate end-of-life recycling and on-site manufacturing. Additionally, fusion joining of these materials can replace adhesives, resulting in stronger and more robust blades. This work showed that, compared to typical adhesives used in wind turbine blades, fusion welding resulted in an increase in both the static and fatigue lap-shear strength as compared to bonded thermoplastic composite coupons. This initial coupon-scale research suggests that there is potential for developing fusion welding techniques for full-scale wind turbine blades.

Modeling multiple failures of composite box beams used in wind turbine blades

Large composite structures, such as composite wind turbine blades, may exhibit multiple failure modes that challenge the modeling strategies and methodologies designers adopt in finite element (FE) analysis. This study develops a comprehensive and general FE modeling method to simulate interactive failure process of composite box beams used in wind turbine blades. The composite box beams are the primary loading-carrying members and could show different failure modes due to competing failure mechanisms. A continuum-damage mechanics based progressive failure analysis approach is developed in three-dimensional stress/strain domain to simulate failure behavior of the box beams. Structural nonlinearities associated with geometry, materials and contact are included. The material failures considered in this study are composite failure with three material failure modes, foam core crushing and adhesive failure. The in-plane shear stress versus strain relation of unidirectional composites is included in the material damage model. Comprehensive comparisons are made between numerical simulations and experimental observations with respect to strain response, ultimate loads, failure modes and failure progress. The modeling approach is found to be capable of predicting both strength and failure of box beams with reasonable accuracy and it exhibits great potential to predict failure response of composite wind turbine blades.