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Recent work demonstrated the benefits of preview wind measurements for turbine control. This paper investigates the basic design tradeoffs between turbine performance, preview time, and pitch actuator rate limits. A Region 3 rotor-speed tracking problem is formulated in continuous-time as an optimal control problem using a simple one-state rigid body turbine model. The exact analytical solution to this problem provides insight into the fundamental performance limits. These analytical results are compared with the performance of an H\infty preview controller simulated on a higher fidelity, nonlinear turbine model with realistic wind sensor models. The performance versus preview time characteristics of the H\infty controllers are in agreement with the predictions from the lower fidelity model. Thus, the analytical results obtained with the low-order model can provide design guidelines for the use of preview information in turbine control. [ABSTRACT FROM PUBLISHER]

Reliability and maintainability of wind turbines are posing new challenges and issues due to advancements in new and sophisticated technologies. This has necessitated development of novel, efficient, and cost-effective strategies for enhancing the availability for power output and operational life. There are certain ways to achieve such objectives where every approach has certain pros and cons. One possible technique is to use the wind speed and power output data for exploring the behavioral similarities of different wind turbines. Based on the similarity measures, a group of turbines may appear together in the form of clusters. This is accomplished by working with the vast piles of data which are pre-processed by using statistical time domain features to provide input to a self-organizing map (SOM) neural network. Based on the clustering results, operational and maintenance strategies are planned for a group of wind turbines in contrast to doing the same work for individual ones. A case study is presented where it has been shown how the information obtained from the clustering analysis would be used for predicting the power output and then developing the optimal operational and maintenance strategies in an integrated manner. [ABSTRACT FROM AUTHOR]

Abstract: The increasing use of small wind energy has made it necessary to develop new methods to improve the efficiency of this technology. This improvement is best achieved considering the interaction between the various components, such as the wind rotors, the electrical generators, the rectifiers and the inverters, as opposed to studying the individual components in isolation. This paper describes a methodology to increase the efficiency of Small Wind Turbines (SWTs) equipped with a Permanent Magnet Synchronous Machine (PMSM). To achieve this objective, capacitor banks will be connected between the PMSM and the rectifier. This methodology is motivated by two clear aims. The first one is to operate the SWT with its maximum power coefficient C p . The second one is to select the most suitable capacitor bank for each wind speed to optimise the energy supplied to the grid. The methodology will be tested on a commercial 3.5kW SWT, and the results will be studied to determine its feasibility. [Copyright &y& Elsevier]

This paper examines the impact of natural and man-made obstructions on local wind conditions and the performance of small wind turbines when impacted by wake effects. The rural site used for this research contains three Skystream 3.7 turbines in close proximity to each other and several buildings. A 13 m meteorological tower with wind speed and direction sensors was installed in a nearby open area. An empirical analysis was conducted to provide a comparison of turbine performance and measured wind speed for each turbine as a function of localized disturbances caused by turbine placement. Turbine proximity to nearby buildings was observed to cause an overall reduction in power production, although cases of apparent wind speed-up induced by the buildings, and increased relative power output, were also observed. A reduction in wind turbine power output due to the wake of an adjacent turbine was observed. Overall, the turbine closest to the buildings produced about 10% less energy during the measurement period than the most distant turbine. This study confirmed the importance of careful micrositing of small wind turbines, and the complexity of the flow field near buildings and wind turbines. [ABSTRACT FROM AUTHOR]

The article focuses on a study conducted to evaluate wind turbine performance and design and optimization of wind farms. It is noted that different measuring techniques were carried, taking into account possible variations of the relative position between the LiDAR measurement volume and wake location.

Dynamically scaled experiments and numerical analyses are performed to study the effects of the wake from an upstream wind turbine on the aerodynamics and peiformance of a downstream wind turbine. The experiments are carried out in the dynamically scaled wind turbine test facility at ETH Zurich. A five-hole steady-state probe is used to characterize the cross-sectional distribution of velocity at different locations downstream of the wake-generating turbine. The performance of the downstream wind turbine is measured with an in-line torquemeter. The velocity field in the wind turbine wake is found to differ signifi-cantly from the velocity field assumed in numerical wake models. The velocity at hub height does not increase monotonically up to the freestream velocity with downstream dis-tance in the wake. Furthermore, the fiowfield is found to vary significantly radially and azi-muthally. The application of wake models that assume a constant axial velocity profile in the wake based on the measured hub-height velocity can lead to errors in annual energy production predictions of the order of 5% for typical wind farms. The application of wake models that assume an axisymmetric Gaussian velocity profile could lead to prediction errors of the order of 20%. Thus modeling wind turbine wakes more accurately, in particu-lar by accounting for radial variations correctly, could increase the accuracy of annual energy production predictions by 5%~20%. [ABSTRACT FROM AUTHOR]

In this paper, a small wind turbine is analyzed. Because usually the manufactures don't provide enough information about the turbine (especially for small turbines), the steps for obtaining this parameters are presented. A Matlab program was written to fulfill this steps and then the whole turbine was simulated in Simulink. The resulted performance curve from simulation was compared with the performance curve from the manufacture's datasheet for validation [ABSTRACT FROM AUTHOR]

The application of variable speed wind generators in hybrid remote area power supply (RAPS) systems provides opportunities for improved voltage and frequency control together with maximum power point tracking (MPPT), where limited research outcomes exist. The study presented in this paper covers two such hybrid systems: 1) permanent magnet synchronous generator (PMSG) and 2) doubly fed induction generator (DFIG) as wind turbine technologies together with a battery storage and a dump load. The battery storage system and dump load are able to assist in maintaining the active power balance during over and under generation conditions as well as sudden load changes. Through simulation studies, it has been demonstrated that both RAPS systems are able to regulate the load side voltage and frequency within the acceptable limits while extracting the maximum power from wind, which is an inherent capability of variable speed generators. The two RAPS systems and their associated control strategies have been developed and their performance is investigated using SimPowerSystems blocksets in MATLAB. [ABSTRACT FROM AUTHOR]

In this paper, simulation models are used to study the performance of small power systems based on different weather parameters. The results are extracted using Matlab software program for analyzing the performance of two wind turbines: Whisper-500 3.2KW and NY-WSR1204 600W which have the same type of permanent magnetic alternators (three phase and 16 poles). Different parameters can affect on the performance of wind turbines which are: the wind speed air density, air pressure, temperature and the length of blades for wind generators. The mathematical results related the previous mentioned parameters are analyzed in order to determine the sensitivity of input power on the output of wind generators. [ABSTRACT FROM AUTHOR]

Small turbines are considered one of the most promising technologies for an effective diffusion of renewable energy sources in new installation contexts with a high degree of integration with human activity (e.g. the urban environment). In these new installations, however, the real working conditions can be far from the nominal ones. In particular, the turbine functioning can be noticeably affected by misalignments between the oncoming flow and the axis of the rotor; differently from horizontal-axis wind turbines, whose performance is decreased by a skew angle, H-Darrieus turbines are thought to take advantage from this condition in some cases.In this study, an improved model for the performance prediction of H-Darrieus rotors under skewed flow was developed. In detail, a theoretical approach based on Momentum Models was properly modified to account for the variations induced by the new direction of the flow which invests the rotor. In particular, the modifications in the aerodynamic characteristics of the airfoils, the swept area and the streamtubes distribution were modeled. The performance predictions of the new model were compared both with experimental data available in the technical literature and with the results of wind tunnel tests purposefully carried out on a full scale model of an H-Darrieus turbine. Notable agreement has been constantly obtained between simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper is focused on the evaluation of five planetary boundary layer (PBL) schemes in the Weather Research and Forecasting model for offshore wind energy purposes. One first order scheme: Yonsey University and four one-and-a-half order schemes: Mellor-Yamada-Janic, Quasi-Normal Scale Elimination, Mellor-Yamada-Nakanishi-Niino, and Bougeault-Lacarrère, are considered. Turbulent flux measurements from the FINO1 platform in the North Sea are used to estimate the Obukhov length, allowing the sorting of the data into different stability classes. In addition, wind LiDAR measurements are used to analyze wind profiles up to 251.5 m, encompassing the heights where today's wind turbines operate. The ability of the different PBL schemes to forecast turbulent fluxes of heat and momentum and surface stability is evaluated. Obukhov length results show that in general, PBL schemes forecast more moderated stable stratifications and a reinforcement of the instability for neutral and convective conditions, compared to FINO1 observations. The vertical structure of the wind speed profile is thoroughly analyzed for stable, near-neutral, unstable, and very unstable conditions by using total shear stresses, eddy diffusivities, and wind speed shears. The Mellor-Yamada-Nakanishi-Niino scheme presents the best agreement with measurements considering the different atmospheric stabilities analyzed. Stable conditions are the most complicated scenario for the PBL schemes to reproduce due to their overdiffusive formulations, which effect is to lower the vertical wind shear. Under such conditions, Quasi-Normal Scale Elimination and Yonsey University outperform the rest of the PBL schemes, the latest using a revised diffusion formulation. [ABSTRACT FROM AUTHOR]

Although the Magnus type wind turbine has many benefits over conventional blade-type wind turbines, it normally has low wind energy utilization efficiency. Therefore, it is important to seek effective ways of improving the Magnus wind turbine power performance in order to promote its application. As blade aspect ratio is a critical parameter influencing the Magnus wind turbine performance, a 3D numerical study of a Magnus type wind turbine which is equipped with cylindrical blades with different aspect ratios has been conducted in this paper. In addition, various cylinder shapes, including truncated cone and wavy cylinder, have also been used and their effects on the performance of the Magnus wind turbine are analyzed. Performance characteristics such as power, torque, and thrust coefficients of the Magnus turbine with different blade shapes are compared and discussed with the aim of identifying the desirable blade characteristics for this type of turbine. [ABSTRACT FROM AUTHOR]

In this article, we present an experimental study in a wind tunnel of a three-bladed, Rutland 503 model, horizontal axis yawed wind turbine. Power measurement and an exploration downstream wake of the turbine using particle image velocimetry measurements are performed. The variation of power coefficient as a function of rotational velocity is presented for different yaw angles. The results show a loss of power from the wind turbine when the yaw angle increases. The velocity field of the downstream wake of the rotor is presented in an azimuth plane, which passes through the symmetry axis of the rotor. The instantaneous velocity field is measured and recorded to allow for obtaining the averaged velocity field. The results also show variations in the wake downstream due to decelerating flow caused by the yawed turbine rotor. Analysis of this data shows that the active control of yaw angles could be an advantage to preserve the power from the wind turbine and that details near rotor wake are important for wake theories and to predict the performance of wind turbines as well. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a review on the performance of Savonius wind turbines. This type of turbine is unusual and its application for obtaining useful energy from air stream is an alternative to the use of conventional wind turbines. Simple construction, high start up and full operation moment, wind acceptance from any direction, low noise and angular velocity in operation, reducing wear on moving parts, are some advantages of using this type of machine. Over the years, numerous adaptations for this device were proposed. The variety of possible configurations of the rotor is another advantage in using such machine. Each different arrangement of Savonius rotor affects its performance. Savonius rotor performance is affected by operational conditions, geometric and air flow parameters. The range of reported values for maximum averaged power coefficient includes values around 0.05–0.30 for most settings. Performance gains of up to 50% for tip speed ratio of maximum averaged power coefficient are also reported with the use of stators. Present article aims to gather relevant information about Savonius turbines, bringing a discussion about their performance. It is intended to provide useful knowledge for future studies. [Copyright &y& Elsevier]

As harvesting of wind energy grows, so does the need for improved forecasts from the surface to the top of wind turbines. To improve mesoscale forecasts of wind, temperature, and dewpoint temperature in this layer, two different approaches are examined. In the first experiment, the vertical resolution of a limited-area model with 2.5-km grid spacing (LAM-2.5 km) is significantly increased near the surface to better represent profiles in that layer. In the second experiment, prognostic variables for land and ocean surfaces are initialized using results from an external land surface model system [the Global Environmental Multiscale Surface system (GEM-Surf)] and from a regional ocean model. Results show that increasing the vertical resolution near the surface leads to improved temperature and dewpoint temperature forecasts at the surface and in the wind turbine layer. For winds, improvements are more modest, because they are limited to the gradient measured across the span of the vertical wind turbine blades. On the other hand, the replacement of operational surface analyses with high-resolution analyses obtained from GEM-Surf is found to improve summer dewpoint temperature forecasts. It is shown that changes in soil moisture analyses explain the bulk of the improved dewpoint forecasts. [ABSTRACT FROM AUTHOR]

Abstract: The aerodynamics of a high solidity vertical axis wind turbine was investigated through wind tunnel tests of a full size turbine operating at Reynolds numbers of Re ≥ 500,000 (where the power production has been shown to be Re independent). Flow visualization using light-weight tufts attached to the inner surface of a blade was used to gain insight on the operating aerodynamics, which is related to the measured power performance. The tufts proved to be an effective and simple technique to observe the flow characteristics on the large scales involved where other flow measurement techniques like particle image velocimetry or laser Doppler velocimetry would be challenging and expensive. Straight blades on the H–Darrieus turbine operating at peak power showed large regions of flow separation on the upwind blade pass extending from early in the upwind pass from an azimuthal angle θ = 40–50° (where the blade is moving directly upwind at θ = 0°) to over 60° into the downwind pass. The effect of preset blade pitch was also investigated where a 6° leading edge toe-out pitch showed a delay in separation initiation and a reduction in the maximum fraction of chord with flow reversal as well as increased power performance. The overall separation behaviour of the straight blades shows the importance of dynamic stall and the interaction of the separated vortex with the blade as mechanisms in lift generation. Performance and flow separation results are presented for canted blades. The flow separation behaviour was considerably different from straight blades, with canted blades experiencing less flow reversal on their upwind pass, and recovering attached flow before θ = 180°. The installation of fences on the canted blades increased the power and reduced the blade speed ratio at which peak power occurred, suggestive of a reduction in spanwise flow on the swept blades (so that they locally behave more like straight blades). However, the location and amount of flow separation did not trend toward that seen with the straight blades, but rather the fences further reduced the amount of separation. [Copyright &y& Elsevier]

Abstract: There is a dichotomy in the view of wind farms among members of the public: on one hand, there is a desire for renewable energy sources, and on the other hand, there is a major concern about the visual impact of wind turbines used for power production. This concern for visual impact is a major factor in the reaction of the public to the development of new wind farms. Our study aims to objectify this influence and to establish the factors that determine how people evaluate these structures. We tested the visual quality of landscapes in which these structures are to be placed, the number of structures and their distance from the viewer, and various characteristics of our respondents. We found that the physical attributes of the landscape and wind turbines influenced the respondents’ reactions far more than socio-demographic and attitudinal factors. One of the most important results of our study is the sensitivity of respondents to the placement of wind turbines in landscapes of high aesthetic quality, and, on the other hand, a relatively high level of acceptance of these structures in unattractive landscapes. Wind turbines also receive better acceptance if the number of turbines in a landscape is limited, and if the structures are kept away from observation points, such as settlements, transportation infrastructure and viewpoints. The most important characteristic of the respondents that influenced their evaluation was their attitude to wind power. On the basis of these results, recommendations are presented for placing wind turbines and for protecting the character of the landscape within the planning and policy making processes. [Copyright &y& Elsevier]

One of the most important factors for cost-effective SB-VAWT product is the selection of an appropriate airfoil to achieve desired aerodynamic performance and to optimise the overall dimensions of the SB-VAWT. Design changes related to airfoil also have the potential for increasing the cost effectiveness of SB-VAWTs. This research aims to perform a detailed performance analysis on a series of low Reynolds number (RN) airfoils selected to enhance the performance of smaller capacity fixed-pitch SB-VAWT. Three low RN airfoils have been selected as candidates for the blades of a smaller-capacity SB-VAWT. The research compares their performances with that of a conventionally used symmetric NACA 0015 airfoil. It was found that all candidate low RN airfoils produced higher torque than the NACA 0015 at lower tip speed ratios. [ABSTRACT FROM AUTHOR]

The near-field to far-field transformation (NFFFT) algorithm from Mensa and Vaccaro is applied to obtain the far-field Doppler signatures of wind turbines based on near-field measurement data. A set of angular window and sampling criteria are derived to aid in the data collection and processing. Simulations are performed to demonstrate the effectiveness of the NFFFT and sampling criteria. Near-field measurements are made of a three-arm wire turbine model and a small commercial turbine. The NFFFT is applied to recover the far-field backscattering. The NFFFT is shown to effectively correct the Doppler features from the wind turbine scattering. The measurement results are corroborated with near-field and far-field simulations. [ABSTRACT FROM PUBLISHER]

The article presents computational computational fluid dynamics (CFD) of the contra rotor wind turbine (CRWT), a dual rotor wind generator. It informs that CFD analysis revealed that wind speed in the direction of upwind primary rotor and downwind secondary rotor of CRWT should be considered for getting aerodynamic feasibility and high-power output.

The article offers information on a study aims to demonstrate a fully automated process for optimizing the airfoil cross-section of a vertical-axis wind turbine (VAWT). It informs that design system for the study consists of an automated hybrid mesh generation tools with unsteady computational fluid dynamics (CFD) simulation software. It further informs that the flexibility of modular design is used to obtain an optimized blade design that maximizes the efficiency of the wind turbine.

The aim of the present paper is to investigate ways of improving the efficiency of a six-bladed Savonius rotor. The efficiency of Savonius machines is low because of the "negative drag" exerted on the convex part of the blades and also because the torque of standard Savonius rotors varies substantially during one rotation and therefore affects the self starting of the rotor at certain wind angles. Improvement of the efficiency of the Savonius rotor is carried out by increasing the number of blades and also by preventing the wind from impinging on the convex parts. The latter can be done by hiding the convex part of the blades behind a shield or a vane. The present paper shows the results of two-dimensional computational fluid dynamics (CFD) computations, indicating a promising increase of the power coefficient from 0.3 to 0.5. [ABSTRACT FROM AUTHOR]

In this paper, the first-ever measurements of the wake of a full-scale wind turbine using an instrumented uninhabited aerial vehicle (UAV) are reported. The key enabler for this novel measurement approach is the integration of fast response aerodynamic probe technology with miniaturized hardware and software for UAVs that enable autonomous UAV operation. The measurements, made to support the development of advanced wind simulation tools, are made in the near-wake (0.5D-3D, where D is rotor diameter) region of a 2 MW wind turbine that is located in a topography of complex terrain and varied vegetation. Downwind of the wind turbine, profiles of the wind speed show that there is strong three-dimensional shear in the near-wake flow. Along the centerline of the wake, the deficit in wind speed is a consequence of wakes from the rotor, nacelle, and tower. By comparison with the profiles away from the centerline, the shadowing effects of nacelle and tower diminish downstream of 2.5D. Away from the centerline, the deficit in wind speed is approximately constant ≈25%. However, along the centerline, the deficit is ≈65% near to the rotor, 0.5D-1.75D, and only decreases to 25% downstream of 2.5D. [ABSTRACT FROM AUTHOR]

A directly irradiated cavity solar reactor devoted to the thermal reduction of SnO2 particle-cloud is studied numerically by using the Monte Carlo method. The steady-state model solves the radiation and convection heat transfers in the semitransparent particle suspension and the chemical reaction. It was used to predict the temperature distribution and the reaction extent inside the cavity, as well as the theoretical thermochemical efficiency for different operational conditions. The simulations assume that the reactor contains a nonuniform size suspension of radiatively participating reacting SnO2 particles. The model takes into account the radiative characteristics of the particles, as well as the directional characteristics of the power distribution of the incoming concentrated solar energy. The particle concentration, the particle size, and the length of the reactor are varied. Results show that the particle temperature and the yield of the endothermic reaction are higher when the reactor is fed with a cloud of particles with average diameter of 20 μm. The maximal thermochemical efficiency reached is 10%, which corresponds to an optimal optical thickness of around 2. [ABSTRACT FROM AUTHOR]

Vertical axis wind turbines have always been a controversial technology; claims regarding their benefits and drawbacks have been debated since the initial patent in 1931. Despite this contention, very little systematic vertical axis wind turbine research has been accomplished. Experimental assessments remain prohibitively expensive, while analytical analyses are limited by the complexity of the system. Numerical methods can address both concerns, but inadequate computing power hampered this field. Instead, approximating models were developed which provided some basis for study; but all these exhibited high error margins when compared with actual turbine performance data and were only useful in some operating regimes. Modern computers are capable of more accurate computational fluid dynamics analysis, but most research has focused on horizontal axis configurations or modeling of single blades rather than full geometries. In order to address this research gap, a systematic review of vertical axis wind-power turbine (VAWT) was undertaken, starting with establishment of a methodology for vertical axis wind turbine simulation that is presented in this paper. Replicating the experimental prototype, both 2D and 3D models of a three-bladed vertical axis wind turbine were generated. Full transient computational fluid dynamics (CFD) simulations using mesh deformation capability available in ANSYS-CFX were run from turbine start-up to operating speed and compared with the experimental data in order to validate the technique. A circular inner domain, containing the blades and the rotor, was allowed to undergo mesh deformation with a rotational velocity that varied with torque generated by the incoming wind. Results have demonstrated that a transient CFD simulation using a two-dimensional computational model can accurately predict vertical axis wind turbine operating speed within 12% error, with the caveat that intermediate turbine performance is not accurately captured. [ABSTRACT FROM AUTHOR]

A Markov model for the performance of wind turbines is developed that accounts for component reliability and the effect of wind speed and turbine capacity on component reliability. The model is calibrated to the observed performance of offshore turbines in the north of Europe, and uses wind records obtained from the coast of the state of Maine in the northeast United States in simulation. Simulation results indicate availability of 0.91, with mean residence time in the operating state that is nearly exponential and has a mean of 42 days. Using a power curve typical for a 2.5 MW turbine, the capacity factor is found to be beta distributed and highly non-Gaussian. Noticeable seasonal variation in turbine and farm performance metrics are observed and result from seasonal fluctuations in the characteristics of the wind record. The input parameters to the Markov model, as defined in this paper, are limited to those for which field data are available for calibration. Nevertheless, the framework of the model is readily adaptable to include, for example: site specific conditions; turbine details; wake induced loading effects; component redundancies; and dependencies. An on-off model is introduced as an approximation to the stochastic process describing the operating state of a wind turbine, and from this on-off process an Ornstein-Uhlenbeck (O-U) process is developed as a model for the availability of a wind farm. The O-U model agrees well with Monte Carlo (MC) simulation of the Markov model and is accepted as a valid approximation. Using the O-U model in design and management of large wind farms will be advantageous because it can provide statistics of wind farm performance without resort to intensive large scale MC simulation. [ABSTRACT FROM AUTHOR]

A floating platform concept is introduced in this paper for offshore wind turbine. A vertical cylinder on the top of an elliptical sphere forms the principal configuration of the platform. The analysis of the dynamic performance of an example platform with 5 MW wind turbine by means of the well-established linear theory for the dynamics of marine constructions in waves shows that the platform is able to secure the normal function of the wind turbine in waves up to rough sea state and has the required dynamic performance for survival in extreme waves by adopting a survival ballast condition. An important feature of this concept is that reinforced concrete can be used as cost-efficient construction material so that the service life, several times longer than similar steel constructions can be obtained despite of the marine corrosive and erosive environment. Thus, this kind of platform can become competitive in the economical, sustainable, and environment-friendly aspect. [ABSTRACT FROM AUTHOR]

Icing on blade surface of the straight-bladed vertical axis wind turbine (SB-VAWT) set in cold regions is a serious problem. To study the performance effects of icing on SB-VAWT, numerical simulations were carried out on the ice accretion on NACA 0015 airfoil which was always used for blade airfoil of SB-VAWT by CFD methods based on 2D steady incompressible N-S Equation. The morphology and procedure of icing on blade airfoil were obtained under different wind speeds, attack angles of blade and water flow flux in wind. The static flow fields, especially the static pressure fields around blade airfoil with or without icing on it were computed. The aerodynamic characteristics including the lift and drag force coefficients of blade airfoil were also calculated. The results indicated that icing caused the static pressure field changed greatly and led to the increasing of drag force and reducing the aerodynamic performance. [ABSTRACT FROM AUTHOR]

Swirling flow is popularly used for flame stabilization in gas turbine combustion chamber. Swirling flow has three velocity components, namely, axial, radial and tangential. Relative strength of axial and radial momentum is described by nondimensional swirl number (S). Reduction in emission level is achieved by setting the correct value of swirl number. The present work reports a numerical study of steady flow through CAN type combustor utilizing swirler vanes. Three-dimensional flow through the combustor geometry with swirler is numerically simulated using FLUENT. Influence of swirler vane angles on flow and mixing characteristics of the combustor is analyzed. The vane angles considered for this analysis are varied between 15° and 60° in steps of 15°. Effect of turbulence is incorporated through k-ϵ model. The larger swirl intensity demands higher pressure for flow. Swirler with 45° vanes is found to have good mixing characteristics with optimum pressure penalties. [ABSTRACT FROM AUTHOR]

The article focuses on the studies of the vibration monitoring of the rolling bearing in the wind generators and turbine gearboxes and its role in maximising asset liability. Topics include the use of the rolling contact bearing of the rotating equipment, the application of vibration monitoring as widely used predictive maintenance technique, and the application of the vibration monitoring on assessing the condition of wind turbine drive train.

No abstract is available for this article. [ABSTRACT FROM AUTHOR]

A modern horizontal axis wind turbine was simulated by means of computational fluid dynamics (CFD) simulations. The analyzed machine has a diameter of 100 m and is immersed in the atmospheric boundary layer (ABL). The velocity and turbulence stratification of the ABL is correctly preserved along the domain by the adoption of modified wall functions. An overset technique is employed to handle the rotation of the turbine rotor throughout the operation of the machine. The ABL induces periodically oscillating loads and generated torque on the rotor blades. Several configurations are analyzed. First, the results of a rotor-only simulation are compared to the ones obtained from the simulation of the full machine in order to evaluate the effect of the supporting structures on the produced torque and on the loads acting on the blades. Then, a tilt angle is introduced on the analyzed rotor and its effect on the oscillating loads of each blade is highlighted by comparing the results to the untilted configuration. Lastly, a yaw misalignment is also introduced and the results are compared to the unyawed configuration. [ABSTRACT FROM AUTHOR]

Pitch angle control is the most common means of adjusting the torque of wind turbines. The verification of its correct function and the optimization of its control are therefore very important for improving the efficiency of wind kinetic energy conversion. On these grounds, this work is devoted to studying the impact of pitch misalignment on wind turbine power production. A test case wind farm sited onshore, featuring five multi-megawatt wind turbines, was studied. On one wind turbine on the farm, a maximum pitch imbalance between the blades of 4.5 ° was detected; therefore, there was an intervention for recalibration. Operational data were available for assessing production improvement after the intervention. Due to the non-stationary conditions to which wind turbines are subjected, this is generally a non-trivial problem. In this work, a general method was formulated for studying this kind of problem: it is based on the study, before and after the upgrade, of the residuals between the measured power output and a reliable model of the power output itself. A careful formulation of the model is therefore crucial: in this work, an automatic feature selection algorithm based on stepwise multivariate regression was adopted, and it allows identification of the most meaningful input variables for a multivariate linear model whose target is the power of the wind turbine whose pitch has been recalibrated. This method can be useful, in general, for the study of wind turbine power upgrades, which have been recently spreading in the wind energy industry, and for the monitoring of wind turbine performances. For the test case of interest, the power of the recalibrated wind turbine is modeled as a linear function of the active and reactive power of the nearby wind turbines, and it is estimated that, after the intervention, the pitch recalibration provided a 5.5% improvement in the power production below rated power. Wind turbine practitioners, in general, should pay considerable attention to the pitch imbalance, because it increases loads and affects the residue lifetime; in particular, the results of this study indicate that severe pitch misalignment can heavily impact power production. [ABSTRACT FROM AUTHOR]

In order to remain competitive, wind turbines must be reliable machines with efficient and effective maintenance strategies. However, thus far, wind turbine reliability information has been closely guarded by the original equipment manufacturers (OEMs), and turbine reliability studies often rely on data that are not always in a usable or consistent format. In addition, issues with turbine maintenance logs and alarm system data can make it hard to identify historical periods of faulty operation. This means that building new and effective data-driven condition monitoring techniques and methods can be challenging, especially those that rely on supervisory control and data acquisition (SCADA) system data. Such data are rarely standardised, resulting in challenges for researchers in contextualising these data. This work aims to summarise some of the issues seen in previous studies, highlighting the common problems seen by researchers working in the areas of condition monitoring and reliability analysis. Standards and policy initiatives that aim to alleviate some of these problems are given, and a summary of their recommendations is presented. The main finding from this work is that industry would benefit hugely from unified standards for turbine taxonomies, alarm codes, SCADA operational data and maintenance and fault reporting. [ABSTRACT FROM AUTHOR]

No abstract is available for this article. [ABSTRACT FROM AUTHOR]

No abstract is available for this article. [ABSTRACT FROM AUTHOR]

High flexibility of new offshore wind turbines (OWT) makes them vulnerable since they are subjected to large environmental loadings, wind turbine excitations and seismic loadings. A control system capable of mitigating undesired vibrations with the potential of modifying its structural properties depending on time-variant loadings and damage development can effectively enhance serviceability and fatigue lifetime of turbine systems. In the present paper, a model for offshore wind turbine systems equipped with a semi-active time-variant tuned mass damper is developed considering nonlinear soil–pile interaction phenomenon and time-variant damage conditions. The adaptive concept of this tuned mass damper assumes slow change in its structural properties. Stochastic wind and wave loadings in conjunction with ground motions are applied to the system. Damages to soil and tower caused by earthquake strokes are considered and the semi-active control device is retuned to the instantaneous frequency of the system using short-time Fourier transformation (STFT). The performance of semi-active time-variant vibration control is compared with its passive counterpart in operational and parked conditions. The dynamic responses for a single seismic record and a set of seismic records are presented. The results show that a semi-active mass damper with a mass ratio of 1% performs significantly better than a passive tuned mass damper with a mass ratio of 4%. [ABSTRACT FROM AUTHOR]