bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance analysis of wind turbines with leading-edge erosion and erosion-safe mode operation
Authors: Barfknecht N , Kreuseler M , de Tavernier D , von Terzi D 
Published: June 2022

Abstract
For offshore wind turbines, Leading-Edge Erosion (LEE) due to rain is posing a serious risk to structural integrity and can lead to a performance loss of the order of a few percent of the Annual Energy Production (AEP). A proposed mitigation strategy is the so-called Erosion-Safe Mode (ESM). In this work, the AEP losses caused by LEE or by operating in the ESM are compared for two reference turbines, i.e. the IEA 15MW and the NREL 5MW turbines. For both turbines, the performance is evaluated in uniform and sheared inflow conditions. The effects of erosion are modeled by creating clean and rough airfoil polars in XFOIL. It is assumed that erosion occurs once a critical blade element section speed is exceeded. Power curves for LEE and ESM are calculated by using the free-wake vortex method CACTUS. Results show that LEE negatively affects the power production below rated capacity, while operating in ESM predominantly sheds performance at rated power of the turbine. This study, therefore, shows that a break-even point for the ESM exists. The AEP loss due to erosion can be successfully mitigated with the ESM at sites with low mean wind speed, however, at sites with higher mean wind speed, operation with erosion leads to a lower AEP loss. The break-even point shows little sensitivity to the blade design and to mean shear variations, but strongly depends on the frequency ESM needs to be applied. The latter is driven by the predicted amount of damaging rain events. In conclusion, erosion-optimal operation is strongly governed by the site characteristics and much less by turbine design, and the viability of an ESM strategy can be significantly expanded by a better understanding of blade damage mechanisms and improved forecasting of the related weather events.
Identification of torsional frequencies of a large rotor blade based on measurement and simulation data
Authors: Wegner Anna , Huhn Matthias L. , Mechler Sebastian , Thomas Philipp 
Published: June 2022

Abstract
With increasing size of wind turbines, the aerodynamic and structural properties of the rotor blades become more and more important. However, studies investigating the torsional properties using measurement data and simulation results on full-size turbines are still scarce. In this study, torsional measurements are carried out on a large wind turbine with a rotor diameter of 180 m and compared with model results. In this study, torsional measurements on a large wind turbine with a rotor diameter of 180 m are conducted and compared with model results. Torsional parameters of a rotor blade are identified using two different measurement methods, the first based on strain gauges and the second based on accelerometers. Both methods show frequencies that can be associated with the natural frequencies of the two first torsional modes of the rotor blade. To extract the natural frequencies and to reduce external effects, a manual pitching procedure is evaluated. Here, the first two natural frequencies associated with torsional modes can be identified. In a second step, the behaviour of the blade during power production is investigated and compared with the simulation results.
Active rotor coning for a 25 MW downwind offshore wind turbine
Authors: Qin Chao (Chris) , Loth Eric , Zalkind Daniel S. , Pao Lucy Y. , Yao Shulong , Todd Griffith D. , Selig Michael S. , Damiani Rick 
Published: June 2022

Abstract
A two-bladed downwind turbine system was upscaled from 13.2 MW to 25 MW by redesigning aerodynamics, structures, and controls. In particular, three 25-MW rotors were developed, and the final version is a fully redesigned model of the original rotor. Despite their radically large sizes, it was found that these 25-MW turbine rotors satisfy this limited set of structural design drivers at the rated condition and that larger blade lengths are possible with conewise load-alignment. In addition, flapwise morphing (varying the cone angle with a wind-speed schedule) was investigated to minimize mean and fluctuating blade root bending loads using steady inflow proxies for the maximum and lifetime damage equivalent load moments. Compared to the fixed coned rotor case, morphing can provide an Annual Energy Production (AEP) increase of 6%, and the maximum blade root flapwise bending moment increases 21% (still under the constraint, i.e., 10% of the ultimate moments) as a trade-off. The resulting series of 25-MW rotors can be a valuable baseline for further development and assessment of ultra-large-scale wind turbines.
Simulating tip effects in vertical-axis wind turbines with the actuator line method
Authors: Melani PF , Balduzzi F , Bianchini A 
Published: June 2022

AbstractSimulation of the complex, unsteady aerodynamics characterizing Darrieus rotors requires computational tools with a fidelity higher than the ubiquitous Blade Element Momentum (BEM) theory. Among them, the Actuator Line Method (ALM) stands out in terms of accuracy and computational cost. This approach, however, still fails to resolve the vortex-like structures shed at the blade ends, overestimating turbine performance at the higher rotational speeds. Moving from this background, in this study a comprehensive investigation on the ALM’s capability to simulate tip effects and their impact on rotor performance is carried out. To this end, the ALM tool developed by the authors in the ANSYS®FLUENT®environment (v. 20.2) and specifically tailored to the simulation of vertical-axis machines was employed. Both a steady finite wing and a fictitious one-blade Darrieus H-rotor, for which high-fidelity blade-resolved CFD data are available as benchmark, were considered as test cases. ALM simulations were first performed without any correction for different cell sizes and force projection radii, so that the limits of the original approach could be assessed. Then, two different sub-models were applied: the classical semi-empirical Glauert correction and a new methodology based on the Lifting Line Theory (LLT), which was recently proposed by Dağ and Sørensen (DS). The latter was here adapted to vertical-axis machines. Eventually, the blade spanwise load profiles coming from the three approaches were assessed and compared, proving the superior performance of the DS model.
Rapid approach for structural design of the tower and monopile for a series of 25 MW offshore turbines
Authors: Escalera Mendoza Alejandra S. , Todd Griffith D. , Qin Chris , Loth Eric , Johnson Nick 
Published: June 2022

Abstract
The goal of further reducing the Levelized Cost of Energy (LCOE) has driven the investigation of large-scale wind turbines. This work presents a simple, rapid and detailed approach for the structural design of the tower and monopile without a controller, but with frequency and high fidelity structural verification. The approach uses an optimization to reduce the mass of the structures while meeting strength, buckling and geometric constraints by using analytical equations. A verification of frequency constraints is performed with BModes, and ANSYS Mechanical APDL is used for high fidelity verification of stress and buckling. The approach is applied to study the design space of three 25 MW offshore wind turbines with different rotor diameters and cone angles, and to evaluate the nacelle center of mass fore-aft location effect. Results obtained show that the tower and monopile are more susceptible to changes in the rotor thrust than the overturning moment even for designs with high pre-cone angle and large distance of the nacelle center of mass from the tower axis. But it is possible to obtain structurally feasible tower and monopile designs for the three 25 MW turbines studied while not exceeding diameter and wall thickness limits. However, mass penalties can be decreased by 0.8-14%, to further reduce the cost of energy, by increasing the diameter limit which may require manufacturing technology development. The approach applied and studies serve to understand the design space of the tower and monopile for a 25 MW turbine, and provide baseline designs that can be used in the development of a controller and evaluation of a full suite of design load cases.
Field tests of a highly flexible downwind ultralight rotor to mimic a 13-MW turbine rotor
Authors: Loth Eric , Ananda Gavin , Chetan Mayank , Damiani Rick , Todd Griffith D. , Johnson Kathryn , Kianbakht Sepideh , Kaminski Meghan , Pao Lucy , Phadnis Mandar , Qin Chao (Chris) , Scholbrock Andy , Selig Michael , Simpson Juliet , Yao Shulong 
Published: June 2022

AbstractOffshore extreme-scale turbines of 20–25 MW in size may offer reduced energy costs. The technical barriers at these extreme scales include escalating blade masses with increased flexibility as well as high gravity loads and tower-strike issues. These barriers may be addressed with a load-aligning downwind turbine. To investigate this type of design, a field test campaign was conducted with an aeroelastically scaled rotor, termed the Segmented Ultralight Morphing Rotor Demonstrator (SUMR-D). The tests were conducted on the Controls Advanced Research Turbine at the National Renewable Energy Laboratory. The paper gives an overviewof the experimental diagnostics, blade design, and results of the field campaign, as well as makes conclusions and recommendations regarding extreme-scale highly flexible downwind rotors.
Investigation of a delta wing Vortex Generator
Authors: Hansen M O L , Rogowski K 
Published: June 2022

Abstract
The flow and the effect on a DU08-W-210 airfoil using a conventional and a delta wing vortex generator (VG) has been investigated numerically using ANSYS Fluent and STAR CCM+ CFD solvers. The numerical results from the two CFD programs are very consistent. Both VG geometries delay boundary separation at the trailing edge of the airfoil and thus increase the lift and lift to drag ratio. The overall aerodynamic loads on the airfoil are quite similar for the two different VG geometries, but the created vortices give a slightly different distribution of the skin friction in the wake behind the VGs. The vortex created by the delta wing VG for the same conditions and size as the conventional triangular VG is slightly stronger and probably caused by the fact that the surface creating the vortices is placed higher up in the boundary layer and thus experience a higher inflow velocity. A method to measure the strength and core radius of the created vortices using a Lamb-Ossen vortex is described.
A simple model to predict the energy loss due to leading edge roughness
Authors: Bak Christian 
Published: June 2022

Abstract
In this paper a simple model to predict losses in annual energy production due to leading edge roughness or leading edge erosion from wind turbines is presented. Because detailed information about wind turbines not always are available, the input to this model requires only a few parameters: rated power, rotor radius, two Weibull parameters and categories of local damages. Therefore, some assumptions are made in the model. It was validated against a common implementation of a BEM code and showed good agreement in the loss of annual energy production.
Also, a categorisation methods was proposed. The categories ranged between a and e corresponding to an undamaged blade and a severely damaged blade, respectively. This categorisation was made locally on the blade. The blade is divided into annular elements and each annular element is graded with a category. By summing up the annular elements on the blade, each with their categories, the total loss in energy production was predicted.
Impact of wind turbine operation conditions on infrasonic and low frequency sound induced by on-shore wind turbines
Authors: Blumendeller Esther , Hofsäß Martin , Goerlitz Arne , Cheng Po Wen 
Published: June 2022

Abstract
In this paper, the influence of wind turbine operation conditions, like rotational speed, nacelle position and output power, on the low- and infrasonic sound emissions at the wind farm and sound immissions at residential buildings will be investigated. For this purpose, parallel measurements were carried out at a wind farm on the Swabian Alb in complex terrain and at four residential locations in the vicinity of the wind farm over a period of two months. Distinctive tones can be assigned to the blade passage at different rotational speeds. Furthermore, tones at 28.9 Hz (rated) and 18.3 Hz (below rated) with two higher harmonics can be attributed to the wind turbine generator. Wind farm infrasonic tones at the blade passing frequency were detected at the wind farm and residential buildings. At the residential buildings infrasonic tones were detected mainly for maximum rotational speed of the wind turbines and seem to be independent from wind direction.
Simulation based prediction of ring creep on a planetary bearing of a 1MW wind turbine gearbox
Authors: Gnauert Jonas , Krause Alexander , Jacobs Georg , Bosse Dennis , Zang Aaron 
Published: June 2022

Abstract
Wind turbines (WT) must be further optimized concerning availability and reliability. One of the major reasons of WT downtime is the failure of gearbox bearings. Some of these failures occur due to the ring creep. Ring creep is a failure mechanism, which is mostly detected in the planetary bearings. Ring creep describes a relative movement of the outer ring to the planetary gear. In order to improve the understanding of ring creep, the finite element method (FEM) is used to simulate ring creep in a full-scale planetary bearing (NJ2330) of a 1MW WT planetary gear. The simulation results are validated with experimental data, obtained on a nacelle test bench. The study shows that the simulative prediction of ring creep is of the correct order of magnitude, but no accurate prediction of ring creep can be made without accounting for manufacturing tolerance classes.
Dynamic Investigations between Two- and Three-bladed Wind Turbines with Various Yaw, Tilt and Cone Angles
Authors: Martínez Vivas A I , Kim T 
Published: June 2022

Abstract
Tilt and cone are included in wind turbine design to increase tower clearance. Yaw misalignments take place often during turbine operation. The combined effects of these parameters modify the relative wind speed experienced by wind turbine blades, thereby altering the turbine’s dynamics. Consequently, power and loads, key design considerations, are affected. In the absence of exhaustive research available on this topic, this paper provides a quantitative analysis on the impact of tilt, cone and yaw on power and loads. The DTU 10MW Reference Wind Turbine and its two-bladed equivalent are evaluated. The results are obtained using the aeroelastic code HAWC2. It is demonstrated that the ultimate and fatigue loads are greater in the two-bladed than in the three-bladed model during operations. Tilt, cone and ±10º yaw reduce the annual energy production by up to 1%. These three parameters generally increase ultimate and fatigue loads. However, the relationship between these parameters and their impact on the bending moments of both wind turbines is complex, and the results are configuration dependent. It is concluded that the combination of these three parameters must be included as part of the design load examination of any target wind turbine.
Development of a Vulnerability Map of Wind Turbine Power Converters
Authors: Tartt K , Kazemi-Amiri A , Nejad A R , McDonald A , Carroll J 
Published: June 2022

Abstract
With the amount of turbines that are already installed and that are planned to be installed in order to meet all the carbon emission objectives set by Governments worldwide, a means of producing a way to determine and highlight weak links or components that are more likely to fail would be extremely beneficial. One way to do this is via vulnerability maps. This paper looks at producing a vulnerability map for the power converter of a wind turbine using maintenance reports. The vulnerability map is a useful means to identify which sub-systems/components to consider when determining lifetime extension of wind turbine drivetrains. All the components that were either replaced or repaired are grouped together to determine their failure rates. Their rates are then ranked from highest to lowest and each component that makes up a typical power converter diagram coloured according to its failure rate, from red for the highest, through to orange, yellow and green for the lowest. The results show that there are three clear components that failed more often than the rest. An additional analysis looks at whether the location of the turbines alter the vulnerability map and this is confirmed. Although the same three components have the highest failure rates, their values change according to which country they are installed.
Aerodynamic Devices to Reduce/Suppress Vortex Induced Vibrations on a Wind Turbine Tower: A Review
Authors: Krishnappa Likith , Sander Aljoscha , Thoben Klaus-Dieter 
Published: June 2022

Abstract
The flow of air over a cylinder at sufficiently high Reynolds number (Re) leads to the formation of vortices. The vortices formed undergoes the process of shedding, exerting lift and drag forces onto the cylinder causing the cylinder to oscillate. These oscillations are termed as Vortex Induced Vibrations (VIV). VIV’s can induce very high fatigue loads onto the structure, leading to its failure. Hence, the suppression/mitigation of these VIV’s is of utmost importance in practical situations. Vortex suppression techniques such as active, passive or compound techniques can be used for the same. This paper focuses on providing a brief overview on the available passive techniques with particular interest in the flow modification, flow separation control devices and their implementation on a wind turbine tower. From this study, it was observed that most of the experimental research related to the testing of the flow modification devices were carried out in a flow channel with water as the flow medium. Therefore, their effectiveness on a wind turbine tower is questionable. However, flow separation control devices were tested in air but these devices have been tested at different Re and therefore their effectiveness cannot be comprehensively compared. The paper concludes by giving a brief overview of the work that will be carried out in the future to tackle this particular problem.
Finite Element Model to Predict the Impact of Wrinkles on Wind Turbine Blades
Authors: Mendonça Heloisa Guedes , Mikkelsen Lars Pilgaard , Branner Kim 
Published: June 2022

Abstract
Among the manufacturing defects of wind turbine blades, wrinkles are critical to the blade performance, affecting the structural integrity. Therefore, this paper introduces three-dimensional numerical models of laminates representative of a wind turbine blade with artificial wrinkles. The models are verified against static tension-compression experimental tests of laminates embedded with two types of wrinkles. The results show a good correlation between numerical prediction and experimentally obtained stiffness behaviour. The outcome of this analysis proves the validity of the numerical modelling strategy applied to evaluate the behaviour of laminates with wrinkles for a static loading situation.
State observer for the deformation state of wind turbine blades based on inertial measurements
Authors: Luthe J , Su Y , Ehret J , Zierath J , Woernle C 
Published: June 2022

Abstract
The design of wind turbines is based on conservative load assumptions compared to the actual load conditions at the designated erection site. As a consequence, structural reserves are very likely at the end of the turbine’s approved life time. To safely exploit these structural reserves, a continuous, model-based fatigue monitoring of the individual wind turbine is necessary. Direct strain measurements are possible at accessible locations only and, moreover, have limited long-term stability. Therefore, an indirect, model-based estimation of structural deformations is proposed that relies on integrated motion measurement with only a minimal number of robust inertial sensors. Tests on a small-scale structural test rig of a wind turbine prove the feasibility of the concept.
Model-free control of the dynamic lift of a wind turbine blade section: experimental results
Authors: Michel Loïc , Neunaber Ingrid , Mishra Rishabh , Braud Caroline , Plestan Franck , Barbot Jean-Pierre , Boucher Xavier , Join Cédric , Fliess Michel 
Published: June 2022

Abstract
This work addresses the problem of developing control algorithms for the control of the aerodynamic lift of wind turbine blades using air injection, taking into account disturbances caused by turbulent perturbations. For this, a test bench is used where the lift of a 2D blade section in a wind tunnel can be controlled by a set of micro-jets close to the trailing edge. Through a continuous, local identification of the lift variations a model-free control that does not need any prior knowledge of the system is proposed. It allows the control of the flow of the micro-jets and stabilizes the lift around a tracking reference. The ability of the proposed control algorithm to track the lift reference when subjected to external perturbations, i.e., gusts, is discussed. In particular, this work demonstrates that the lift can be set to particular values using the proposed control strategy, and can be re-stabilized to pre-gust lift conditions. Experimental results illustrate globally the feasibility of such a control.
Wind Turbine Power Curve Modelling using Gaussian Mixture Copula, ANN Regressive and BANN
Authors: Lázaro Roberto , Yürüşen Nurseda Y. , Melero Julio J. 
Published: June 2022

Abstract
In terms of monitoring wind turbine performance, the power curve plays a key role and it is a valuable indicator of the wind turbine’s condition as it allows the identification of anomalies related to production. On the other hand, by calculating a typical reference curve of the machine, it is possible to calculate losses and estimate its performance. A suitable model that characterises the power curve can benefit the estimated production of a wind turbine or wind farm. The most widely used models to characterise power curves are based on 2-variable models (wind speed and power). The power curve is affected by different exogenous variables (such as temperature, wind direction or turbulence intensity) that must be taken into account in the characterisation of the power curve. Consequently, the working conditions of the wind turbine are different depending on the site, and multivariable models that can take these variables into account are required. Currently new models and alternatives are emerging. This study will evaluate the performance of multivariate models based on Gaussian mixture copula model (GMCM), Regressive artificial neural Networks (ANN) and Bayesian artificial neural networks (BANN) in terms of power curve characterisation and power estimation. The results will be compared to the most common methods such as the manufacturer power curve and historical power curve, which is generated using the the bins method. Taking advantage of the benefits of neural networks (NN), particular types of NN have been considered to provide the value of uncertainty in the estimation of power.