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An experimental and numerical investigation into the influence of wind effects on wind turbines with tubular towers
Abstract
This study delves into investigating the profound impact of wind loads on the structural integrity of wind tur-
bines. To comprehensively assess the influence of wind loads, a two-pronged approach was adopted: first, a
meticulously crafted 1/100 scale model was employed within a wind tunnel, and second, advanced numerical
simulations based on computational fluid dynamics (CFD) were conducted. Moreover, the study takes into ac-
count the intricate factor of turbine proximity in the wind tunnel setup. The design of the tower structure takes
into consideration an array of loads, including lateral and gravitational forces. Notably, a substantial load arises
from the rotational force generated by blade motion, which exerts its effects on the structure. Calculations of this
force were executed using ABAQUS software. This multifaceted analysis involves the application of angular
velocity to the blades, subsequently enabling the computation of time-dependent support reactions via dynamic
numerical analysis employing the Newmark method. Furthermore, the study encompasses the determination of
static equivalent forces. It is noteworthy that the maximum displacement experienced by the structure coincides
with the initial phase of blade movement.
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Europe has set an ambitious target to increase the offshore wind power capacity to approximately 30 GW by 2026. With nearshore locations already allocated, future wind farms must be installed in deeper waters, pushing the operational limits of currently used jack-up vessels. Utilizing existing floating heavy-lift vessels presents a viable alternative. This paper disseminates data gathered during the full-scale testing campaign of a floating installation of an offshore wind turbine tower. For this purpose, novel time-synchronized motion-tracking units were developed. Analysis of the obtained data reveals that approximately 96% of the motion response of the tower is due to wave action and 3% to vortex-induced vibrations caused by the presence of a passive tugger line, which shifted one of the system’s natural frequencies towards the tower’s vortex-shedding frequency. Next to wind and wave-induced motion, the data reveal that the hoisting itself induces tower vibrations, accounting for less than 1% of the tower motion response. The collected data offer a distinctive perspective on this type of installation, which is unlikely to be replicated at model scale due to the scaling limitations associated with the interdependence of waves and wind. The data can be used to validate motion control strategies to enhance the efficiency, safety, and workability of floating offshore wind turbine installations.
This paper numerically investigates the effect of pulsating flow on the settling dynamics of rigid circular particles. This is an interdisciplinary subject and spans several areas ranging from mathematical and numerical modeling to fluid mechanics. For this purpose, pulsatile flow characteristics are embedded in the combination of the direct‐forcing immersed boundary method and the split‐forcing lattice Boltzmann method. Inter‐collision forces between the solid boundaries (particles and boundaries) and the added mass force due to acceleration are considered. Adequate verification tests are done to ensure the credibility of the findings. The critical parameters of pulsating flow, such as amplitude and frequency of pulsation, are investigated in detail. The paper especially puts emphasis on the interaction between particles and studies the well‐known drafting, kissing, and tumbling (DKT) phenomena. Two different scenarios are taken into account and also compared with the stationary flow. The first case is when the pulsating flow is in the direction of gravity (co‐flow), while in the latter, there is an opposing flow (counterflow). The sedimentation manners of 12 particles in a vertical channel are also presented. The findings shed light on the importance of pulsating flow and the extension of the proposed computational method for such problems. It is also revealed that pulsation and its variables can alter DKT by either postponing or speeding up the process. Also, in some cases, the cycle of DKT can be maintained incompletely, and particles would just stick together. The results can be useful for various engineering problems like filtration and particle sorting.
The geometry of a building is one of the influential parameters in calculating the wind load. This parameter is denoted as Cp in static methods. It is provided in codes for conventional buildings. The present study calculates the wind pressure coefficient for a non-conventional Y-shaped building model with a scale of 1:500. To obtain the wind effects on the building, the wind tunnel test and computational fluid dynamics (CFD) were employed. The model was rotated in 10-degree rotation steps within the wind tunnel to find the most critical wind load orientation. Also, the wind pressure was applied to the building in the CFD approach to obtain the maximum displacement. The largest displacement (relative to the original position at θ = 0°) was found to be 3.75 at θ = 30°. The numerical results were found to be in good agreement with the experimental wind tunnel results. This demonstrated that the proposed method could be a suitable alternative to the wind tunnel test.
The use of wind turbines for renewable energy production has gained considerable relevance in the last 2 decades, especially in countries prone to Earthquakes (Mexico, Chile, USA, Japan, etc.), mainly due to cost reduction and their positive environmental impact. The rapid development of this industry has led to the constant growth of the wind turbines size (tower height, rotor diameter and nominal power). Therefore, the suitable understanding of the structural behavior requires a careful analysis in order to predict the expected maximum loads for seismic design purposes. One of the most controversial aspects in seismic design of wind turbines has been how to combine seismic and aerodynamic loads when these actions are assessed in an uncoupled way (seismic load assessed through spectral modal analysis). ASCE/AWEA RP2011 [5] recommends combining both loads applying a reduction load factor of 0.75 to the direct sum (for steel towers). Asareh [9] and Santangelo et al [10] have proposed that the combination of seismic and aerodynamic loads with load factor of 0.75 can provide results sufficiently close to the coupled response. However, Prowell [7] and Meng et al [8] have shown that the combination rule proposed by ASCE/AWEA underestimates the response, and the square root of the sum of the squares (SRSS) gives better results compare to the coupled response (for steel towers). International codes such as IEC 61400-1 [3] and GL [6] establish that both loads must be combined applying a load factor of 1.0 to the direct sum. Lately, IEC 61400-1-2019 [4] has proposed that when seismic load is evaluated through response spectrum method, then the aerodynamic load is added using the SRSS method. Regardless these specifications provide some seismic guidance typical wind turbine guidelines are not intended to provide a deep seismic understanding therefore the seismic issue is not properly addressed. This work presents a comparative analysis between coupled response of seismic and aerodynamic loads and their uncoupled analysis. Coupled simulations have been carried out with the FAST open software (time-history analysis) considering the new generation of large turbines supported on steel, concrete and hybrid towers. On the other hand, seismic uncoupled response has been evaluated using FAST and SAP2000 software separately. For seismic analysis, several accelerations records generated by different seismic-tectonic mechanism have been used (shallow crustal, subduction interface and subduction intraplate sources). The results obtained shows a high dispersion on data, which is highly dependent on the wind turbine type (fundamental period and dynamic response), seismic-tectonic source (frequency content, strong motion duration) and the relative weigh between seismic and aerodynamic loads. Based on our results, a new proposal of combination rules of seismic/aerodynamic loads is made, which provides a better matching between coupled and uncoupled response.
Wind turbine blades are designed to be thin and flexible elements. Because unstable dynamic behaviour can affect the life of the rotor, it is crucial to understand the instability of non-linear behaviour caused by large deflections. The present study undertakes both a stability analysis of the non-linear response and an experimental validation of a simplified model for a wind turbine blade based on a cantilever beam. The model is formulated taking into account large geometric deflections and assuming a Galerkin approach. The model is validated experimentally in a wind tunnel with aluminium beams of differing geometry. Analysis of the dynamic response using phase planes reveals that the degree of instability is related to the amplitude of the excitation and the stiffness characteristics.
This paper presents a numerical method for the simulation of fluid-structure interaction specifically tailored to interactions between Newtonian fluids and a large number of slender viscoelastic Cosserat rods. Because of their high flexibility and low weight the rods considered here exhibit large deflections, even under moderate fluid loads. Their motion, in turn, modifies the flow so that fluid and structures are strongly coupled to each other which is numerically very challenging. The paper proposes a new coupling approach based on an immersed boundary method which improves upon existing methods for this problem. It is numerically stable and exempt from any global iteration between the fluid part and the structure part, thus yielding high stability and low computational cost of the coupling scheme. The contribution presents the underlying methodology and its algorithmic realization, including an assessment of accuracy and convergence by systematic studies. Various validation cases illustrate performance and versatility of the proposed method.
Ducted Wind Turbines (DWTs) can be used for energy harvesting in urban areas where non-uniform inflows might be the cause of aerodynamic and acoustic performance degradation. For this reason, an aerodynamic and aero-acoustic analysis of DWTs in yawed inflow condition is performed for two duct geometries: a baseline commercial DWT model, DonQi, and one with a duct having a higher cross-section camber with respect to the baseline, named DonQi D5. The latter has been obtained from a previous optimization study. A numerical investigation using Lattice-Boltzmann Very-Large-Eddy Simulations is presented. Data confirm that the aerodynamic performance improvement, i.e. increase of the power coefficient, is proportional to the increase of the duct thrust force coefficient. It is found that, placing the DWT at a yaw angle of 7.5 , the aerodynamic performances of the DonQi D5 DWT model are less affected by the yaw angle. On the other hand, this configuration shows an increase of broadband noise with respect to the baseline DonQi one, both in non-yawed and yawed inflow conditions. This is associated to turbulent boundary layer trailing edge noise due to the turbulent flow structures developing along the surface of the duct.
Accurate simulation of wind turbine wakes is critical for the optimization of turbine efficiency and prediction of fatigue loads. These wakes are three-dimensional, complex, unsteady and can evolve in geometrically complex environments. Modeling these flows calls thus for high-quality numerical methods that are able to capture and transport thin vortical structures on an unstructured grid. In this work, an immersed boundary (IB) method for solving fluid flow problems of aligned wind turbines under uniform inflow is shown. A finite element method is used starting from a base mesh which does not represent exactly the blade of the wind turbine (non body-conforming mesh). At each time step, the base mesh is locally modified to provide a new mesh fitting the boundary of the rotor blades. The mesh is also locally improved using edge swapping to enhance the quality of the elements and ensure high accuracy of simulation. The methodology is assessed on two different test cases and validated with experimental results.
Wind turbines life time is commonly predicted based on statistical methods. However, the success of statistics-based maintenance depends on the amount of variation in the system design, usage and load. Life time prediction based on physical models seeks to overcome this drawback by considering the actual design and evaluating the specific usage, load and operating condition of the considered systems. In this paper, a load-based maintenance approach is proposed to predict wind turbines life time. Physical models are used to evaluate load profiles at wind turbine blade root, rotor hub center and tower head. The effects of surface roughness, side winds, yaw misalignment, rotor tilt and blade cone angle, individual blade pitching and wind turbulences are considered and quantified. It is shown that centrifugal, gravity, Euler and Coriolis accelerations dominate the blade root loads. Tilt and cone angle, as well as individual blade pitching, affect the rotor hub and dynamic tower head loads. Further, the actual wind speed distribution is considered which is also proven to be a critical life time prediction parameter. Finally, a set of parameters is proposed that need to be monitored in a specific wind turbine to enable the practical implementation of a predictive maintenance policy.
In this study, the feasibility of vibration-based damage assessment in a wind turbine tower (WTT) with gravity-based foundation (GBF) under various waves is numerically investigated. Firstly, a finite element model is constructed for the GBF WTT which consists of a tower, caisson, and foundation bed. Eigenvalue analysis is performed to identify a few vibration modes of interest, which represent complex behaviors of a flexible tower, rigid caisson, and deformable foundation. Secondly, wave-induced dynamic pressures are analyzed for a few selected wave conditions and damage scenarios are also designed to simulate the main components of the target GBF WTT. Thirdly, forced vibration responses of the GBF WTT are analyzed for the wave-induced excitation. Then modal parameters (i.e., natural frequencies and mode shapes) are extracted by using a combined use of time-domain and frequency-domain modal identification methods. Finally, the variation of modal parameters is estimated by measuring relative changes in natural frequencies and mode shapes in order to quantify the damage-induced effects. Also, the wave-induced variation of modal parameters is estimated to relatively assess the effect of various wave actions on the damage-induced variation of modal parameters.
The computational fluid dynamics (CFD) method is widely used today for determining the wind action on structures. Along with the CFD method the wind tunnel experiments are also employed to achieve this purpose. The cost and effort required for a wind tunnel test, however, is much higher than that of the CFD method; therefore, it is beneficial to extend and validate the use of CFD method to various classes and types of structures. This paper firstly compares the results of CFD method with the results of three series of wind tunnel tests available in the literature. Then, numerically the effect of structural flexibility and the neighbourhood of the objects on the wind pressure distribution coefficients are studied. Two and three half spheres are arranged sequentially and transversally. According to the CFD analysis, at a clear distance greater than 2.5 times the diameter of the (obstructing) dome, the wind dynamic interference effects on the reference hemisphere are diminished.
The goal of this work is twofold: 1) to determine the angular deflection and displacement of the NREL 5 MW reference wind turbine tower under different atmospheric thermal stratifications, and under overlapping wind turbine wake effects using a comprehensive numerical analysis; 2) to develop and verify a generalized analytical model allowing to efficiently estimate wind turbine tower displacements under a variety of flow conditions. Large-eddy simulations are used to generate atmospheric flows similar to those of a characteristic diurnal cycle. One hour periods are selected and inputted into an aero-elastic simulation code which resolves the rotor-disk aerodynamic loading components, which are then used as inputs to a 3-D finite element model of the tower to compute the angular deflection and displacement. To improve efficiency in tower displacement predictions, a generalized analytical model is developed based on a simplified 2-D cantilever beam and 1-D momentum theory. Results are compared with those obtained from the numerical simulations. Results indicate that the tower deflection standard deviation increases with increasing atmospheric turbulence and wake superposition. Also, differentiated tower displacements are experienced under different atmospheric stratifications. Interestingly, lone standing wind turbines undergo larger tower deflections compared to those located within very large wind farms. The wind turbine rotor thrust and the aerodynamic thrust on the tower are found to have the greatest and least influence, respectively, on tower deflection. Displacement results from the finite element analysis are used to verify the accuracy of the new generalized analytical model showing a very good agreement. This new model has the advantage of estimating the tower deflection by just knowing the inflow velocity for any wind turbine, independent of the atmospheric stratification and wind farm arrangement.
The paper presents a new model of turbulence in which the local turbulent viscosity is determined from the solution of transport equations for the turbulence kinetic energy and the energy dissipation rate. The major component of this work has been the provision of a suitable form of the model for regions where the turbulence Reynolds number is low. The model has been applied to the prediction of wall boundary-layer flows in which streamwise accelerations are so severe that the boundary layer reverts partially towards laminar. In all cases, the predicted hydrodynamic and heat-transfer development of the boundary layers is in close agreement with the measured behaviour.
Modeling and direct numerical simulation of particle-laden flows have a tremendous variety of applications in science and engineering across a vast spectrum of scales from pollution dispersion in the atmosphere, to fluidization in the combustion process, to aerosol deposition in spray medication, along with many others. Due to their strongly nonlinear and multiscale nature, the above complex phenomena still raise a very steep challenge to the most computational methods. In this review, we provide comprehensive coverage of multibody hydrodynamic (MBH) problems focusing on particulate suspensions in complex fluidic systems that have been simulated using hybrid Eulerian-Lagrangian particulate flow models. Among these hybrid models, the Immersed Boundary-Lattice Boltzmann Method (IB-LBM) provides mathematically simple and computationally-efficient algorithms for solid-fluid hydrodynamic interactions in MBH simulations. This paper elaborates on the mathematical framework, applicability, and limitations of various 'simple to complex' representations of close-contact interparticle interactions and collision methods, including short-range interparticle and particle-wall steric interactions, spring and lubrication forces, normal and oblique collisions, and mesoscale molecular models for deformable particle collisions based on hard-sphere and soft-sphere models in MBH models to simulate settling or flow of nonuniform particles of different geometric shapes and sizes in diverse fluidic systems.
The problem of a flapping filament mounted to a free cylinder provides insight into computational fluid dynamics. We study the extent to which the length of the flexible filament and the non-Newtonian power-law fluids should be implemented to stabilize the flapping of an immersed structure in the flow with the Reynolds number of 100. We propose a hybrid model that includes an explicit Lattice Spring Model and Immersed Boundary non-Newtonian Lattice Boltzmann Method to simulate the behavior of the filament in the vicinity of a fluid flow. We validate this hybrid model using bench-marked problems, where a non-Newtonian fluid flow passes over a fixed cylinder in an unconfined channel and in a Newtonian flow over a cylinder containing a flexible fin. In the result section, we study the effects of fluid and structural characteristics on the motion of the filament and cylinder. When shear-thinning, Newtonian, and shear-thickening fluids are used, the results show that the cylinder keeps its minimum distance to the channel centerline at a specific length. This is due to the flapping of the filament generating the low-pressure region downstream from the cylinder and filament structure. We also analyze the effects of the bending stiffness. We find that from the lowest bending stiffness of 0.003 to the highest of 0.007, flexibility has no impact on the cylinder's center of mass, when the filament length is set as large as the critical length. The vibration amplitude and frequency of the filaments are also measured in different fluids and in varied filament stiffnesses. When n = 0.7, the bending stiffness of 0.007 causes a high-frequency vibration with the highest amplitude, whereas a bending stiffness of 0.005 achieves the minimum amplitude.
Accurate numerical models of the flow around wind turbines is highly relevant for optimizing the energy efficiency of wind farms. The main goal of this work is to apply large eddy simulation (LES) along with an immersed boundary (IB) method to generate spatial and temporal information of the velocity field and forces acting on a fully-resolved NREL S809 airfoil and NREL Phase VI wind turbine. The numerical framework used in the simulations performs LES under a Cartesian block-structured mesh that is dynamically refined via adaptive mesh refinement (AMR) to increase accuracy and reduce computational costs. The mesh refinement criteria is based on Lagrangian points and vorticity. Solid surfaces of the wind turbine are captured using the Lagrangian formulation of the IB method. The simulations are based on the NREL Phase VI wind turbine, where blade analysis of lift and drag coefficients were performed, followed by time-averaged streamwise velocity and vorticity evaluations. For different angles of attack, the wake centerline velocity analysis demonstrates high energy extraction in the near wake of the wind turbine blade. In terms of validation, the drag coefficient of the NREL S809 airfoil achieves better agreement with the experimental data than the lift coefficient. Validation from the NREL Phase VI shows that the power performance difference between the simulation and experiment is lower than 6%. Wake analysis of the wind turbine scenario are based on downstream profiles of the time-averaged streamwise velocity. The numerical simulation shows a higher loss of kinetic energy in the near wake region, mainly in the centerline, compared to benchmark data, but achieves very similar results to literature in the far-wake region.
The aerodynamic performance of newly planned as well as existing wind turbines can be improved by eliminating stall. Vortex generators (VGs) can effectively delay air separation occurring on the inboard-section of the wind turbine blade. Many scholars have investigated the principle of VGs in terms of flow control and validated their ability to enhance efficiency. This paper provides a comprehensive review of state-of-the-art VGs that have been tested in the wind turbine field. The basic principle of VG-related flow control is first illustrated, followed by reviews of previous studies regarding the effects of geometric parameters on VG behavior, the effects of VGs on dedicated airfoils for wind turbines, and parametric VG models. The paper also discusses aerodynamic factors impacting the behavior of VGs on wind turbine blades. Future research directions are proposed.
As one of the fastest-growing renewable energy sources, wind power is promoting the global primary energy structure to accelerate towards the direction of cleanliness and low-carbon. Considering that the construction and installation cost of an offshore wind power foundation account for 35%–55% of the development cost of an offshore wind farm, the innovation in foundation forms and their installation technologies is of great significance. In this paper, more than 280 works on the topic of offshore wind turbine installation processes are reviewed, the latest progress and development trend in this field are summarized. The integrated installation technology based on a wide and shallow suction bucket foundation is focused, which has already been widely commercialized. First, three kinds of installation method are described, including the component installation method, partially integrated installation method, and integrated installation method. Second, the existing floating wind turbine infrastructures and their installation methods are summarized, respectively. Third, from the aspects of force mechanism, design principle, control method, monitoring results and economy, the integrated floating and installation technology based on the wide and shallow suction bucket foundation is analyzed comprehensively. Finally, the technical challenges in the future are discussed, and the latest research progress in possible solutions is introduced. This review aims to provide reference for the design of offshore wind power foundations and the development of integrated installation technology.
The installation of wind turbines in urban sites requires consideration of the wind characteristics affecting the energy production (turbulence, environment roughness due to the surrounding buildings …), the self-starting capability and the type, hence the performance, of the wind turbine. In this paper, a three-dimensional CFD analysis of an aerodynamic Savonius wind turbine is performed under steady wind conditions. The inclusion of a deflector was also investigated, and the performance compared to the initial design.
Results of the 3D analysis showed that an optimized axisymmetric deflector improves the power coefficient in all wind directions and over the entire operating range of the turbine. The deflector also increased the average starting torque by 30%, thus extending the operating range of the turbine with respect to the wind speed.
A comparative study of the effectiveness of an innovative optimised nacelle on fatigue loads alleviation and performance improvement in both upwind and downwind configurations has been conducted. The idea is to optimise wind turbine nacelles using flaps to push the flow towards outer spans, which leads to improved turbine performance, as well as mitigates unsteady loads, therefore, extending the fatigue life of wind turbine's components. Theoretical explanations indicate that in the case of upwind configuration, increasing downstream velocity leads to a reduction in turbine power. However, lower wind speeds seen by inner spans lead to mitigate thrust load generated by inner spans. In the case of downwind configuration, increasing upstream velocity leads to improve turbine power based on the turbine Euler equation, and pushing flow towards outer spans with higher lift/drag ratios leads to mitigate unsteady loads generated by inner spans. Experimental results show that using flaps to optimise the nacelle shape not only mitigates unsteady loads and therefore extends the fatigue lifetime of blades but also improves turbine power and yaw stability. Furthermore, using flaps in downwind configuration can compensate for the adverse effect of wind turbine yaw misalignment on the wind turbine performance and unsteady loads.
In this paper we present a full-scale experimental field study of the effects of floater motion on a main bearing in a 6 MW turbine on a spar-type floating substructure. Floating wind turbines are necessary to access the full offshore wind power potential, but the characteristics of their operation leave a gap with respect to the rapidly developing empirical knowledge on operation of bottom-fixed turbines. Larger wind turbines are one of the most important contributions to reducing cost of energy, but challenge established drivetrain layouts, component size envelopes and analysis methods. We have used fibre optic strain sensor arrays to measure circumferential strain in the stationary ring in a main bearing. Strain data have been analysed in the time domain and the frequency domain and compared with data on environmental loads, floating turbine motion and turbine operation. The results show that the contribution to fluctuating strain from in-plane bending strain is two orders of magnitude larger than that from membrane strain. The fluctuating in-plane bending strain is the result of cyclic differences between blade bending moments, both in and out of the rotor plane, and is driven by wind loads and turbine rotation. The fluctuating membrane strain appears to be the result of both axial load from thrust, because of the bearing and roller geometry, and radial loads on the rotating bearing ring from total out-of-plane bending moments in the three blades. The membrane strain shows a contribution from slow-varying wind forces and floating turbine pitch motion. However, as the total fluctuating strain is dominated by the intrinsic effects of blade bending moments in these turbines, the relative effect of floater motion is very small. Mostly relevant for the intrinsic membrane strain, sum and difference frequencies appear in the measured responses as the result of nonlinear system behaviour. This is an important result with respect to turbine modelling and simulation, where global structural analyses and local drivetrain analyses are frequently decoupled.
Operations and maintenance of offshore wind turbines (OWTs) play an important role in the development of offshore wind farms. Compared with operations, maintenance is a critical element in the levelized cost of energy, given the practical constraints imposed by offshore operations and the relatively high costs. The effects of maintenance on the life cycle of an offshore wind farm are highly complex and uncertain. The selection of maintenance strategies influences the overall efficiency, profit margin, safety, and sustainability of offshore wind farms. For an offshore wind project, after a maintenance strategy is selected, schedule planning will be considered, which is an optimization problem. Onsite maintenance will involve complex marine operations whose efficiency and safety depend on practical factors. Moreover, negative environmental impacts due to offshore maintenance deserve attention. To address these issues, this paper reviews the state-of-the-art research on OWT maintenance, covering strategy selection, schedule optimization, onsite operations, repair, assessment criteria, recycling, and environmental concerns. Many methods are summarized and compared. Limitations in the research and shortcomings in industrial development of OWT operations and maintenance are described. Finally, promising areas are identified with regard to future studies of maintenance strategies.
A detailed numerical study has been carried out to investigate the effects of leadingedge protuberance as a novel flow-separation control-technique for vertical-axis-windturbine (VAWT). The aerodynamic performance of a stationary protuberanced blade and an associated H-type Darrieus VAWT made of three protuberanced blades were investigated using unsteady Reynolds-Averaged-Navier-Stokes (URANS) and Implicit Large Eddy Simulation (ILES) methods. The current study involves a comprehensive set of five different types of sinusoidal leading-edge protuberances with three different wavelengths and amplitudes. It is found that this passive flow-control-method can favourably change lift and drag at stall and post-stall regions, which is of high importance for VAWTs. Static stall variation can be changed from leading-edge-stall type to trailing-edge-stall type. This is attributed to a “bi-periodic” phenomenon over the blade suction side and a reduced turbulence kinetic-energy production. Protuberance amplitude was found to be more important than the wavelength in improving aerodynamic performance. Of all the tested cases, the protuberance with amplitude of 1% chord-length (c) and wavelength of 2.5%c behaves the best. The leading-edge protuberance can significantly increase VAWT power-coefficient at low tip-speed-ratios, which are dominated by post-stall conditions. The dynamic stall was delayed and the coherent spanwise wavy flow-structures on the blade suction-side were observed.
Renewable energy is one of the fastest growing segments of energy consumption and wind energy is one of the most widely used sources of renewable energy. There is, however, much less known about the main drivers of wind energy consumption at the country level. This paper uses the logarithmic mean Divisia index (LMDI) method to study the driving factors in wind energy consumption for a group of 17 countries (Australia, Canada, China, Denmark, France, Germany, Greece, India, Ireland, Italy, Japan, Netherlands, Portugal, Spain, Sweden, United Kingdom, and the United States) that are major consumers of wind energy. The renewable energy share component has the largest impact on wind energy consumption. Improvements in energy intensity are the largest driver of reductions in wind energy consumption. Wind energy consumption forecasts for each country in the business as usual (BAU) scenario for the years 2018–2025 show that compound annual growth rates (CAGRs) for wind energy consumption are highest for Canada, Sweden, China, and Germany. Countries that have high shares of renewable energy like Spain, Portugal, and Denmark have low forecast values of CAGRs. Wind energy forecasts are also calculated for a high growth rate scenario and a low growth rate scenario. Future increases in wind energy consumption are going to depend upon the continued increase in renewable energy share which in turn is affected by energy policy designed to promote fuel switching from fossil fuels to renewables.
The wake effect is a major and complex problem in the wind power industry. Wake steering, such as controlling yaw angles of wind turbines, is a proven approach to mitigate the wake influence and increase the power generation of a wind farm. This paper proposes a power prediction model and optimizes yaw angles to minimize the entire wake impact on wind turbines. The power model adopts the artificial neural network (ANN)with the consideration of the wake effect, so it is called ANN-wake-power model. The model can estimate the total power generation of wind turbines for given wind speeds, wind directions, and yaw angles. A case study has been conducted to introduce the modelling process. The experimental data of five wind turbines from an operating wind farm have been used to train and evaluate the model. The ANN-wake-power model has proven to be effective in estimating the power generation. It performs a good balance between computational cost and accuracy. Subsequently, the model is applied to optimize the yaw angles by using Genetic Algorithm. With the optimized yaw angle strategy, the total power ratio of wind turbines can reach 0.96 in all directions involved. For a row of wind turbines, the optimal yaw control strategy for each wind turbine is different. Finally, it is worth noting that, to achieve a good performance of the ANN-wake-power model, sufficient input data should be adopted in the training process.
Wind energy as one of the renewable energies is serving as an indispensable role in generating new electric power. The worldwide installation of wind farms has considerably increased recently. To extract more wind resources, multi-megawatt wind turbines are usually designed and constructed with large rotors and slender tower. These flexible structures are susceptible to external dynamic excitations such as wind, wave and seismic loads. The excessive vibrations can compromise the wind energy conversion, lead to the structural fatigue damage and even result in the catastrophic failure of wind turbines in harsh environmental conditions. Various control devices have been proposed and used to mitigate the unwanted vibrations of wind turbines to enhance their safety and serviceability. This paper aims to provide a state-of-the-art review of the current vibration control techniques and their applications to wind turbines. Firstly, the widely used control strategies in engineering structures are briefly introduced. Their applications to suppress the adverse vibrations of the structural components of wind turbines, mainly the tower and blades, are then reviewed and discussed in detail. It can be concluded that the vibration mitigation of wind turbines is very challenging due to the fact that the dynamic behaviours of wind turbines are very complicated, which are associated with the aerodynamics, rotation of the blades, interaction between the tower and rotating blades, and soil-structure interaction, etc. Moreover, it is a challenge to straightforwardly use many of the conventional control devices because of the limited spaces in the tower and blades.
Energy seems to be the world’s one, the only and the most important problem at the moment. To be specific it’s the production of energy in an ecological, economical and renewable manner, which is keeping the researchers very busy and up all night. Since more than half a century, researchers have been looking into ways of developing power with inexhaustible, replenishable and ecological means.To this end almost from the dawn of modern technology natural resources have been exploited. In the past nature was exploited in its modified state. That is by building dams and river wheels/turbine. Now though the emphasis on extracting energy from the nature while leaving it relatively unaffected. For having environmentally friendly renewable energy sources researchers have been looking to harness the power of the sun and the wind. There is a huge abundance of these two sources. However solar energy being available only a fraction of the time of the day, wind energy having chosen a suitable location can be continuous.Once a location for wind energy convertors or wind turbines has been chosen the research then turns to convert the energy efficiently, cheaply and safely. Also the use of offshore wind resources where the turbines are placed in the seas are studied. It is seen that offshore units have their advantages the most important of which is the freeing up of space on land for agriculture, industry and housing. Once offshore, why stop near the coast? Why not go into deeper waters and capture the energy available in open seas also. Hence wind energy extraction technology is ever developing to find exploitable areas.This PhD research work entitled “Identification and characterization of mechanical and structural properties under static damage and fatigue of a composite floating wind turbine blade” looks into the various aspects of the floating wind turbine blade design. Experimental and numerical techniques are developed to accelerate the design process and possible design optimization proposals are also given.
Wave tank testing is a crucial step during the development of floating offshore wind concepts. Scaled prototypes are engineered to represent the most important phenomena related to the fluid-structure interaction. Nevertheless, in the case of floating wind turbines, the interaction between turbine aerodynamics and platform hydrodynamics presents important challenges that need to be considered. A new hybrid system focused on floating wind turbine tank testing is presented in this paper. It is based on a variety of fans, a multi-fan, which allows the high-fidelity reproduction of a wide range of wind turbine aerodynamics. One of the main advantages of the new methodology proposed, is the possibility to include other loading aside from thrust and wind turbine torque. The most important aerodynamic loads are represented. In fact, it has been demonstrated that wind turbine thrust can be captured with less than 0.5% error compared to the theoretical value. It is also possible to simultaneously model the thrust, torque and shear moments on the rotor within an error below 2%. The multi-fan system deploys a fast rate of change, up to 35N/s, guaranteeing the scaled dynamics. In unsteady wind speeds using 4% of atmospheric turbulence, 94% of the total energy is captured.
This chapter deals with loads on wind turbine blades. It describes the load generating process, wind fields, and the concepts of stresses and strains. Aerodynamic loads, loads introduced by inertia, gravitation and gyroscopic effects, and actuation loads are discussed. The loading effects on the rotor blades and how they are interconnected with the dynamics of the turbine structure are highlighted. There is a discussion on how stochastic loads can be analysed and an outline of cycle counting methodology. The method of design verification testing is briefly described.
Cracks in onshore wind power foundations: causes and consequences
- Hassanzadeh