Large Horizontal Axis Wind Turbine Research Articles

The influence of dynamic pitching on the aerodynamic performance of large horizontal axis wind turbines

To delve into the aerodynamic changes of wind turbines during pitching, this study employs the user-defined function (UDF) and dynamic mesh technique. The dynamic aerodynamic performance of a 3.3 MW turbine blade during variable pitch is investigated via numerical simulation. The results show that the optimal pitch angle increases with increasing incoming wind speed. At the initial and final stages of pitch change, the wind turbine experiences the influence of impact loads, leading to minor fluctuations in torque and thrust coefficients. Within the dynamic pitch change process, the pitch angle notably affects the aerodynamic performance of airfoils at blade x/ c = 0~0.6 c cross sections. The primary stress area of the airfoil contracts, with the blade root experiencing comparatively less impact. In the constant-wind-speed pitching scenario, the low-speed region in the immediate wake of the wind turbine diminishes, resulting in a 10.7% enhancement in the average wind speed at 2.5D wake.

Research of biomimetic corrugation on the blade flutter suppression in large-scale wind turbine systems

Aiming at the blade flutter of large horizontal-axis wind turbines, a method by utilizing biomimetic corrugation to suppress blade flutter is first proposed. By extracting the dragonfly wing corrugation, the biomimetic corrugation airfoil is constructed, finding that mapping corrugation to the airfoil pressure side has better aerodynamic performance. The influence of corrugation type, amplitude λ, and intensity on airfoil flutter is analyzed using orthogonal experiment, which determines that the λ has the greatest influence on airfoil flutter. Based on the fluctuation range of the moment coefficient ΔC m, the optimal airfoil flutter suppression effect is obtained when the type is III, λ= 0.6, and intensity is denser (n = 13). The effective corrugation layout area in the chord direction is determined to be the leading edge, and the ΔC m of corrugation airfoil is reduced by 7.405%, compared to the original airfoil. The application of this corrugation to NREL 15 MW wind turbine 3D blades is studied, and the influence of corrugation layout length in the blade span direction on the suppressive effect is analyzed by fluid-structure interaction. It is found that when the layout length is 0.85 R, the safety margin S f reaches a maximum value of 0.3431 Hz, which is increased 2.940%. The results show that the biomimetic corrugated structure proposed in this paper can not only improve the aerodynamic performance by changing the local flow field on the surface of the blade, but also increase the structural stiffness of the blade itself, and achieve the effect of flutter suppression.

Application of simple harmonic motion theory to the prediction of floating wind turbine first order motions

An alternative solution for achieving a high stability floating foundation for supporting large horizontal axis wind turbines is compared against current floating offshore wind solutions. The testing of a 1:36th scale model of the solution, called Starfloat, in the wind/wave basin of the Cantabria Coastal and Ocean Basin, Santander and the design of this physical model, including scaling issues, is discussed. A method for calculating the added mass of entrained water in heave and surge and the added mass moment of inertia in pitch for semi-submerged cylindrical columns is presented and the computed natural periods of motion are compared against physical trial measurements obtained from motion decay tests. The wave forces exciting the simple harmonic motion are calculated and the resultant approximate solution for the uncoupled floating platform motions in heave, pitch and surge are compared against response amplitude operator curves obtained from the physical model trials, showing reasonable correlation. The importance of depth correction for wave particle velocities and accelerations is very evident and emphasises the need for physical models to be exposed to the correct orbital particle motions over the water column if measured pitch and surge motions are to be a realistic representation of full scale performance.

Analytical prediction of the cross-sectional shear flow in non-prismatic inhomogeneous beamlike solids

Non-prismatic beamlike elements are widespread in engineering applications. Unfortunately, analytical methods commonly used for stress analyses in prismatic beams provide mispredictions in non-prismatic cases. Referring for instance to components like towers and blades of large horizontal axis wind turbines, whose main length is much larger than the dimensions of the tapered transverse cross-sections, the cross-sectional taper produces shear stress distributions that are quite different from those obtainable by formulas valid in prismatic beams, notwithstanding the slender shape of such components, the limited magnitude of their tapering slopes, and the possible Navier-like distribution of their cross-sectional normal stresses. Here, we address the analytical determination of the cross-sectional stresses in elements of this kind, which are slender, non-prismatic, inhomogeneous, and susceptible to large deflections. Recalling the results of a recent work by the author, the field equations that govern the state of stress in the considered elements are exploited to obtain a new closed-form expression of the cross-sectional shear flow, which, in turn, can be used for stress predictions. Comparisons with results of non-linear 3D-FEM analyses for elements mimicking the shape of components used in applications confirm the effectiveness of the proposed analytical approach and formulas.

Sustainability Assessment of Wind Farms

Sustainable energy solutions are becoming increasingly popular as the shift away from conventional fuel-based energy solutions continues. Solar, wind, and hydro solutions are the most frequently used renewable energy sources. Modern wind energy solutions are usually constructed using a design of a large three-bladed horizontal axis wind turbine (HAWT). The blades are upwind facing, which helps support the turbine tower against environmental strain and torque ripple produced from the spinning motion of the blades. HAWTs are usually organised into large groups referred to as wind farms. Wind farms are becoming increasingly popular with their ability to adapt to offshore and onshore environments. In both scenarios, wind turbines have a relatively low footprint, with the land underneath still available to be utilised for agricultural and aquacultural purposes. This paper investigates the sustainability of wind farms by surveying a range of papers. The papers will cover the development, construction, and continued operation of wind turbines providing insights into the sustainability issues. Reviewing these papers will allow for an informed revision to the code of sustainability for future implementations of wind farms. The paper concludes with a case study to apply the suggested sustainability code in a contextual scenario and recommendations for the general engineering profession.

Optimal Design of Wind Turbine Blades by Combination of Multi-airfoil Leaf Elements

This paper takes the blades of a large horizontal axis wind turbine as the research object, selects NACA series airfoil elements for combination, arranges and distributes them according to the thickness and curvature of each airfoil, and generates a new blade that is different from a single airfoil. The aerodynamic performance of the two blades was compared and analyzed by using Qblade software to verify the effectiveness of the method, and the wind energy utilization rate was improved while ensuring the strength of the blade roots.

Effect of Yaw Angle on Large Scale Three-blade Horizontal Axis Wind Turbines

Offshore Horizontal Axis Wind Turbines (HAWT) are used globally as a source of clean and renewable energy. Turbine efficiency can be improved by optimizing the geometry of the turbine blades. Turbines are generally designed in a way that its orientation is adjustable to ensure the wind direction is aligned with the axis of the turbine shaft. The deflection angle from this position is defined as yaw angle of the turbine. Understanding the effects of the yaw angle on the wind turbine performance is important for the turbine safety and performance analysis. In this study, performance of a yawed HAWT is studied by computational fluid dynamics. The wind flow around the turbine is simulated by solving the Reynolds-Averaged Navier-Stokes equations using software ANSYS Fluent. The principal aim of this study is to quantify the yaw angle on the efficiency of the turbine and to check the accuracy of existing empirical formula. A three-bladed 100-m diameter prototype HAWT was analysed through comprehensive Computational Fluid Dynamics (CFD) simulations. The turbine efficiency reaches its maximum value of 33.9% at 0° yaw angle and decreases with the increase of yaw angle. It was proved that the cosine law can estimate the turbine efficiency with a yaw angle with an error less 10% when the yaw angle is between –30° and 30°. The relative error of the cosine law increase at larger yaw angles because of the power is reduced significantly.

Health Monitoring and Diagnosis System for a Small H-Type Darrieus Vertical-Axis Wind Turbine

As the wind power market grows rapidly, the importance of technology for real-time monitoring and diagnosis of wind turbines is increasing. However, most of the developed technologies and research mainly focus on large horizontal-axis wind turbines, and research conducted on small- and medium-sized wind turbines is rare. In this study, a novel low-cost and real-time health monitoring and diagnosis system for the small H-type Darrieus vertical axis wind turbine is proposed. Turbine operating conditions were classified into parked/idle and power production. In the case of the power production condition, abnormality diagnosis was performed using key monitoring parameters, including vibration, fundamental frequency, the bending stress of the tower and generator vibration. The turbine abnormalities were diagnosed in two stages by applying the alert and alarm limits, determined by referring to international standards and material properties and the long-term measurement data together.

Model free adaptive control of large and flexible wind turbine rotors with controllable flaps

This paper investigates the dynamic load alleviation in large and flexible horizontal axis wind turbine rotors with trailing edge flaps, actuated through a novel proportional-derivative model-free adaptive control (PD-MFAC) system. First an aeroservoelastic wind turbine model is developed, which is the combination of a structural model for the tower and blades represented by geometrically non-linear composite beams, and an aerodynamic model for the rotors using an unsteady strip-theory airfoil model. Then three independent model-free controllers are developed to actuate the trailing-edge flaps mounted on three blades, using the blade root-bending moment (RBM) as control input. Comparison is given by an H-infinity (H∞) reference controller and a Gain-scheduled proportional-integral (GS-PI) controller. Simulation results show that the MFAC flap controller provides more effective load alleviation performance in blade root-bending moment than the H∞ and the GS-PI flap controllers, and it also exhibits marked reductions in blade tip deflection (BTD), in the presence of external disturbances.

Numerical simulation of Savonius rotors used for low wind speed application

Traditionally wind energy is popularly harvested using large horizontal axis wind turbines however there performance is found to be limited for unsteady and low-speed wind flow conditions. On contrary, vertical axis wind turbines are found to be superior for low wind speed conditions, which are generally found in crowded urban areas. This paper aims to present a design and numerical analysis of a vertical axis wind turbine that can be used in small-scale urban applications like wind trees. Hence in this paper, to absorb maximum wind energy available, we have selected wind tree applications for which three types of vertical axis rotor design are numerically studied. A Computational Fluid Dynamics simulation is performed on three different geometrical configurations: Savonius helical bach rotor, simple Saonius rotor, and simple bach rotor to predict their performance. The coefficient of power, coefficient of moment, and power produced by these three rotors are evaluated. A MATLAB-based Simulink model is developed to evaluate the power produced by these three rotors and results are compared with CFD results for validation purposes. From our study, it can be observed that the helical-type Bach rotor performed better than the other two, simple Saonius rotor and simple bach rotor considered.

Investigating the aeroelasticity effects on aeroacoustics and aerodynamics of a MW-class HAWT

Abstract Employing large Horizontal Axis Wind Turbines, HAWTs, is inevitable for increasing the wind power generation per turbine unit, i.e. reducing the cost of wind energy production. The consequences of large HWATs application are considerable aeroelastic blade deformation and high levels of aeroacoustic noise generation. In this paper, considering the aeroelastic effects, aeroacoustic calculation of a MW class HAWT is performed by implementing a transient two-way partitioned Fluid-Solid Interaction (FSI) technique. The CFD-FEM and structural modeling are validated using AOC 50/15 HAWT experimental data. Aerodynamic and aeroacoustic simulations of WP_Baseline 1.5 ​MW HAWT are conducted. The results show the power amount and the noise level generated by the flexible blades are about 2.7% and 0.74 ​dB less than those generated by the rigid blades.

Shape memory alloy‐based centrifugal stiffening for response reduction of horizontal axis wind turbine blade

The aim of this study is to reduce the deformation of large horizontal axis wind turbine blades using shape memory alloy (SMA)-based centrifugal stiffening. A discrete model considering dominant modes of the tower, drive train and blades is developed in this study to demonstrate the performance of the proposed stiffening strategy. Here, super-elastic behaviour of SMA is characterized by Graesser-Cozzarelli model. Aerodynamic loads acting on the blades are evaluated using blade element momentum theory. The response is simulated using aerodynamic damping, which is estimated in each mode of vibration. Numerical results presented in this paper clearly show the significance of the proposed SMA-based stiffening to reduce blade vibration. Sensitivity analysis is also carried out to demonstrate the performance envelop of the proposed stiffening strategy over the operational range of the benchmark 5-MW wind turbine. The study clearly highlights the performance enhancement in terms of deformation in two orthogonal directions and design in terms of longitudinal stress that ultimately improve the serviceability of the blade.

An improved dynamic stall model and its effect on wind turbine fatigue load prediction

Due to the nature of the atmospheric boundary layer, large Horizontal-Axis Wind Turbines (HAWTs) generally operate in highly unstable environment, leading to nonstationary loads on HAWT structures. Therefore, it is important to accurately estimate the nonstationary loads to ensure appropriate design boundaries. In this paper, an improved dynamic stall model based on the Beddoes-Leishman (B-L) model is proposed for the estimation of nonstationary aerodynamic loads. The B-L model is modified to account for the characteristics of wind turbine aerofoils which operate at lower Mach numbers and have a larger thickness-to-chord ratio compared to aviation aerofoils. Validation of the model is performed extensively through simulations of the S809 aerofoil under pitch oscillation with different mean angles of attack, oscillating amplitudes and reduced frequencies. To understand the effects of the modifications introduced to the dynamic stall model on the aerodynamic fatigue loads over the lifetime of a wind turbine, a load analysis of a 2 MW HAWT is conducted. The load analysis uses the Blade-Element Momentum (BEM) theory in conjunction with the dynamic stall models. The presented modified dynamic stall model is applicable to wind turbine aerofoils with relative thicknesses greater than 15%.

Effect of rotor–tower interaction, tilt angle, and yaw misalignment on the aeroelasticity of a large horizontal axis wind turbine with composite blades

AbstractThis paper presents a detailed analysis of the rotor–tower interaction and the effects of the rotor's tilt angle and yaw misalignment on a large horizontal axis wind turbine. A high‐fidelity aeroelastic model is employed, coupling computational fluid dynamics (CFD) and structural mechanics (CSM). The wind velocity stratification induced by the atmospheric boundary layer (ABL) is modeled. On the CSM side, the complex composite structure of each blade is accurately modeled using shell elements. The rotor–tower interaction is analyzed by comparing results of a rotor‐only simulation and a full‐machine simulation, observing a sudden drop in loads, deformations, and power production of each blade, when passing in front of the tower. Subsequently, a tilt angle is introduced on the rotor, and its effect on blade displacements, loads, and performance is studied, representing a novelty with respect to the available literature. The tilt angle leads to a different contribution of gravity to the blade deformations, sensibly affecting the stresses in the composite material. Lastly, a yaw misalignment is introduced with respect to the incoming wind, and the resulting changes in the blade solicitations are analyzed. In particular, a reduction of the blade axial displacement amplitude during each revolution is observed.

Flow control based 5 MW wind turbine enhanced energy production for hydrogen generation cost reduction

Improving the performance and the production of renewable energy sources, especially the wind energy, is considered an attractive approach to reduce the Cost of Energy (COE) associated to the hydrogen generation process. In this context, flow control strategies have been object of detailed investigation during last years. Originally flow control devices were designed to be implemented in the aeronautical sector. Nonetheless, the optimization of the performance of the wind turbine blades with the introduction and implementation of these devices is being widely investigated these days. An analysis of the influence of implementing Vortex Generators (VGs) and Gurney Flaps (GFs) in Wind Turbine Blades (WTBs) on the Annual Energy Production (AEP) of large Horizontal Axis Wind Turbine (HAWT) is proposed in this paper. For that purpose, the Weibull distributions of annual wind speed data series of a real wind farm have been calculated, and Blade Element Momentum (BEM) based calculations have been performed to evaluate the effect of the flow control devices on the power curve and the AEP of the NREL offshore 5 MW Baseline Wind Turbine. The obtained results show an enhancement of the AEP of the turbine of 2.43% during year 2015 and 2.68% during year 2016. As a result, increments of the generated hydrogen volume larger than 130000 Nm3 are achieved during both years with no considerable additional cost in the design of the wind turbine.

Fluid–Structure Interaction Simulations of a Wind Gust Impacting on the Blades of a Large Horizontal Axis Wind Turbine

The effect of a wind gust impacting on the blades of a large horizontal-axis wind turbine is analyzed by means of high-fidelity fluid–structure interaction (FSI) simulations. The employed FSI model consisted of a computational fluid dynamics (CFD) model reproducing the velocity stratification of the atmospheric boundary layer (ABL) and a computational structural mechanics (CSM) model loyally reproducing the composite materials of each blade. Two different gust shapes were simulated, and for each of them, two different amplitudes were analyzed. The gusts were chosen to impact the blade when it pointed upwards and was attacked by the highest wind velocity due to the presence of the ABL. The loads and the performance of the impacted blade were studied in detail, analyzing the effect of the different gust shapes and intensities. Also, the deflections of the blade were evaluated and followed during the blade’s rotation. The flow patterns over the blade were monitored in order to assess the occurrence and impact of flow separation over the monitored quantities.

Airfoil design for large horizontal axis wind turbines in low wind speed regions

Abstracts Low wind speed technology helps to reduce the cost of energy, but also creates huge challenge on the wind turbine blade design. To essentially address the particular blade requirements in low wind speed regions with high inflow turbulence, this study extends previous airfoil design optimization methods. Firstly, special design criteria were proposed besides traditional considerations, concerning efficiency, loads, noise and in particular the high inflow turbulence effects on the enlarged blades. Then through improved mathematic models and modified auto optimization platform, an extended airfoil design optimization framework dedicated to low wind speed sites was established. The case design results show that key features of the new airfoil tailed to low wind speed sites are effectively enhanced: the design lift coefficient and lift-to-drag ratio are fairly increased, and the maximum lift coefficient is well constrained. In addition, the acoustic parameter of the new airfoil is successfully reduced. More important is that the airfoil performance sensitivity to surface roughness and inflow turbulence intensity are evidently eliminated. These finally contribute to an improved overall performance. The rotor blade performance evaluation with the new design airfoil in further verified the case design. Results indicate the proposed framework is able to design special airfoils suited for site-specific blade requirements, contributed by the customized considerations, parameterization model, robust calculation method and global algorithms.

Nonlinear Aeroelastic Analysis of Large Wind Turbines Under Turbulent Wind Conditions

We investigate in this Paper the nonlinear aeroelastic response of large horizontal axis wind turbines under a stochastically simulated turbulent wind field, which is instantaneously sampled by the rotating and deforming blades of the rotor. The aeroelastic code combines the unsteady blade element momentum theory, equipped with several important corrections, with the displacement-based nonlinear finite element implementation of the geometrically exact beam theory. The structural model is both shearable and extensible and does not place any restrictions on the magnitudes of the configuration variables or those of the resulting one-dimensional strain measures. The aeroelastic coupling takes into account the beam axis deformations, elastic twist, and vibration-induced velocities. The three-component, three-dimensional turbulent wind field is obtained using the Mann spectrum, from which the instantaneously sampled wind speeds are extracted by spatiotemporal interpolation in the spirit of Taylor’s frozen turbulence hypothesis. The structural and unsteady aerodynamic analysis components of the aeroelastic code are validated using benchmark examples. A fully coupled nonlinear aeroelastic simulation is carried out for the National Renewable Energy Laboratory’s 5 MW research wind turbine. The influence of three-dimensional instantaneous sampling, transverse (lateral and vertical) components of turbulence, vertical wind shear, and flow unsteadiness on the aeroelastic response under turbulence is examined along with the effects of coupling parameters including the vibration-induced velocities and elastic twist of the rotor blades. The dominant frequency contributions in key aeroelastic response variables due to each of these effects are identified.

Dynamic load and stress analysis of a large horizontal axis wind turbine using full scale fluid-structure interaction simulation

A dynamic load and stress analysis of a wind turbine is carried out using transient fluid-structure interaction simulations. On the structural side, the three 50 m long commercial glass-fiber epoxy blades are modelled using shell elements, accurately including the properties of the composite materials. On the fluid side, a hexahedral mesh is obtained for every blade and for the hub of the machine. These meshes are then overlaid to a structured background mesh through an overset technique. The displacements prescribed by the structural solver are imposed on top of the rigid rotation of the turbine. The atmospheric boundary layer (ABL) is included using the k-epsilon turbulence model. The computational fluid dynamics (CFD) and computational solid mechanics (CSM) solvers are strongly coupled using an in-house code. The transient evolution of loads, stresses and displacements on each blade is monitored throughout the simulated time. The ABL induces oscillating axial displacements in the outboard region of the blade. Furthermore, the influence of gravity on the structure is accounted for and investigated, showing that it largely affects the tangential displacement of the blade. The oscillating deformations lead to sensible differences in the torque provided by each blade during its rotation.

Wind‐induced fatigue of large HAWT coupled tower–blade structures considering aeroelastic and yaw effects

SummaryAn efficient approach for predicting wind‐induced fatigue in large horizontal axis wind turbine coupled tower–blade structures subject to aeroelastic and yaw effects is presented. First, aerodynamic loads under yaw conditions are simulated based on the harmonic superposition method and modified blade element momentum theory, in which wind shear, tower shadow, tower–blade interactions, aeroelastic, and rotational effects are taken into account. Then, a nonlinear time‐history of wind‐induced responses under simulated aerodynamic loads is obtained. Finally, based on these results, wind‐induced fatigue damage and lifespan are predicted according to linear cumulative damage theory. For completeness, the influences of mean wind speed, aeroelasticity, and yaw angle on horizontal axis wind turbine fatigue life are discussed. The results indicate that the aerodynamic loads and residual fatigue life can be estimated accurately by the proposed model, which can be used to simulate the 3D wind fields of wind turbines under given wind conditions. The wind energy of the wind turbine blade is mainly concentrated at its edge and is weaker at the hub. Estimation of wind turbine fatigue life is therefore suggested to be based on the component with the shortest life, being the blade root. Furthermore, yaw conditions significantly shorten fatigue life and should not be ignored. Fatigue life is also rather sensitive to mean wind speed.