bluuebunny/crossref_metadata_2025_split huggingface dataset:
A numerical study of Vertical Axis Wind Turbine performances in twin-rotor configurations
Authors: Guilbot M , Barre S , Balarac G , Bonamy C , Guillaud N 
Published: September 2020

Abstract
Placing two counter-rotating rotors of a Vertical Axis Wind Turbine (VAWT) can lead to a significant power enhancement and a faster wake resorption. This global power output is directly related to the spacing between both rotors permitting a mutual confinement effect. In addition, the relative direction of angular velocity of both rotors can strongly impact the overall performances of the machine. A range of two-dimensional (2D) Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations has been managed in order to study the aerodynamic interactions occurring in a pair of VAWT. By comparing with a single-rotor of VAWT, it has been shown than the global power enhancement of a double-rotor VAWT is linked with an extension of the lift production range in one of the two first quartiles of the upwind path. Moreover, the region of the extra power generation seems to be dependant on the relative rotational directions of counter-rotating rotors. In all cases, the extent of lift generation can be associated with a suppression of the cross-stream velocity induced by the confinement of the neighbouring turbine. This local flow perturbation, closed to the inner region, leads to an augmentation of the incidence experienced by the blades in the upwind path, increasing the global lift and torque recovered by the turbine.
Large wind turbine edge instability field validation
Authors: Volk Dillon M. , Kallesøe Bjarne S. , Johnson Scott , Pirrung Georg R. , Riva Riccardo , Barnaud Félix 
Published: September 2020

Abstract
Wind turbines can exhibit flutter-like edgewise instabilities past a critical rotor speed. These edgewise instabilities are dominated by an edge-torsion coupling due to flapwise blade deflection. This paper experimentally validates the predicted stability limit of a 7 MW machine. State of the art simulation software is used to compare against recorded test data and characterize the observed flutter mechanism. The critical rotor speed at which the edgewise instabilities occur at in field measurements can be predicted by time domain simulations and stability analysis with very good agreement.
Assessing wind turbine energy losses due to blade leading edge erosion cavities with parametric CAD and 3D CFD
Authors: Castorrini A. , Cappugi L. , Bonfiglioli A. , Campobasso M.S. 
Published: September 2020

Abstract
Wind turbine leading edge erosion is a complex installation site-dependent process that spoils the aerodynamic performance of wind turbine rotors. This gradual damage process often starts with the formation of pits and gouges leading ultimately to skin delamination. This study demonstrates the application of open source parametric CAD functionalities for the generation of blade geometries with leading edge erosion damage consisting of pits and gouges. This capability is key to the development of high-fidelity computational aerodynamics frameworks for both advancing knowledge on eroded blade aerodynamics, and quantifying energy losses due to erosion. The considered test case is an offshore 5 MW turbine featuring leading edge pit and gouge damage in the outboard part of its blades. The power and loads of the nominal and damaged turbines are determined by means of a blade element momentum theory code using airfoil force data obtained with 3D Navier-Stokes computational fluid dynamics. An annual energy loss between about 1 and 2.5 percent of the nominal annual energy yield is encountered for the considered leading edge damages. The benefits of adaptive power control strategies for mitigating erosion-induced energy losses are also highlighted.
Estimating a nonparametric data-driven model of the lift on a pitching wing
Authors: Siddiqui M F , Decuyper J , Csurcsia P Z , Ertveldt J , Troyer T De , Schoukens J , Runacres M C 
Published: September 2020

Abstract
In aerodynamics, as in many engineering applications, a parametrised mathematical model is used for design and control. Often, such models are directly estimated from experimental data. However, in some cases, it is better to first identify a so-called nonparametric model, before moving to a parametric model. Especially when nonlinear effects are present, a lot of information can be gained from the nonparametric model and the resulting parametric model will be better. In this article, we estimate a nonparametric model of the lift force acting on a pitching wing, using experimental data. The experiments are done using the Active Aeroelastic Test Bench (AATB) setup, which is capable of imposing a wide variety of motions to a wing. The input is the angle of attack and the output is the lift force acting on the NACA 0018 wing. The model is estimated for two different types of input signal, swept sine and odd-random multisine signals. The experiments are done at two different pitch offset angles (5° and 20°) with a pitch amplitude of 6°, covering both the linear and nonlinear aerodynamic flow regime. In the case of odd-random multisines nonlinearity on the FRF is also estimated. We show that the level and characterisation of the nonlinearity in the output can be resolved through a nonparametric model, and that it serves as a necessary step in estimating parametric models.
Modeling the static and dynamic characteristics of a wind turbine airfoil and validation with experimental data
Authors: Bangga Galih , Kampers Gerrit , Weihing Pascal , Arnold Matthias , Kühn Timo , Hölling Michael , Lutz Thorsten 
Published: September 2020

Abstract
Dynamic stall modeling remains one of the most difficult topic in wind turbine aerodynamics despite its long research effort in the past. In the present studies, comprehensive investigations involving CFD, engineering models and experimental data were performed within the joint collaborative work DSWind. Both static and dynamic characteristics of a pitching wind turbine airfoil under a turbulent boundary layer flow were considered. The results indicate that optimized time-accurate CFD calculations can serve as reference data for verifying the engineering models, which can be potentially used for tuning the models under different air flow conditions.
Application of flow control using plasma actuator to horizontal axis wind turbine
Authors: Matsuda T , Maeda T , Kamada Y , Ushigusa T , Kobayashi H , Tanaka M 
Published: September 2020

Abstract
In this study, the clarification of the effect of plasma flow control on the rotor performance was carried out as a wind turbine control technology. The flow fields around rotor and the loads acting on wind turbine were measured by wind tunnel test using a test wind turbine with plasma actuator. As a result, in the low tip speed ratio, the power coefficient of Plasma On is larger than that of Plasma Off and the thrust coefficient of Plasma On slightly increased. In particular, the remarkable increase in the power coefficient was 24% at the most effective tip speed ratio. The wind turbine thrust increased slightly in the low tip speed ratio regime, but was less affected by the plasma flow control. In addition, when the power coefficient and thrust coefficient were calculated using the velocity components of the flow field around the wind turbine, the same tendency as in the wind turbine performance test was shown.
Validation of noise propagation models against detailed flow and acoustic measurements
Authors: Shen Wen Zhong , Sessarego Matias , Cao Jiufa , Nyborg Camilla M , Hansen Kurt S , Bertagnolio Franck , Madsen Helge A , Hansen Per , Vignaroli Andrea , Sørensen Thomas 
Published: September 2020

Abstract
In this paper, four noise propagation models including the parabolic-equation based WindSTAR model, ray-tracing based Nord2000 model, Danish regulation BEK 135 model and ISO 9613-2 standard model are validated against flow and acoustic measurements of a sound source created from a speaker located at a turbine hub of 109 m height. The flow was measured with a fully instrumented met-mast at 350 m and 218 degrees from the turbine tower base. The sound was measured with 11 microphones: 8 were along a line of 45 degrees and a distance up to 1200 m away from the sound source, 3 were located at IEC positions, and 1 microphone close to the speaker, which was used to measure the source strength. White noise and 1/1 band-limited white noise sound at 2 different wind shears with exponents of 0.12 and 0.23 are used for validation. Results show that an overall agreement between experiment and computation is reached for all the numerical models. Among the 4 numerical models, Nord2000 gives the best prediction for the nearfield microphones of mic 4-mic 6 and WindSTAR gives the best prediction for the far-field microphones of mic 7 and mic 8.
Improvement of the pitch bearing load distribution by shape-optimized stiffening plates
Authors: Loriemi A , Jacobs G , Bosse D , Zweiffel M 
Published: September 2020

Abstract
Due to a small cross-sectional dimension compared to their diameter, pitch bearings have a comparably low stiffness. Therefore, surrounding structures strongly influence the internal load distribution of the bearing. By the use of stiffening plates, the load situation of pitch bearings can be positively affected. With a gradient-based optimization procedure regarding contact force and contact angle distribution, an optimized plate shape is determined. This optimized shape provides at the same time a more equalized load distribution, while minimizing the effect of contact ellipse truncation.
Passive self-aligning of a floating offshore wind turbine
Authors: Netzband S , Schulz CW , Abdel-Maksoud M 
Published: September 2020

Abstract
The development of floating offshore wind turbines opens the way for various new design types, and the platform, tower and turbine can benefit from its floating foundation. Self-aligning platforms, where the entire structure follows the wind direction are a promising concept. A single point mooring with turret system allows for free rotation around the vertical axis. Aerodynamic forces of rotor and tower induce the self-aligning moment. In the present study, the operating principle of a passive platform design with airfoil-shaped tower and downwind rotor is analyzed under steady conditions using a boundary element method (BEM). Rotor cone angle and the tower dimensions have a major influence on the yawing moment. They must be large enough to dominate the hydrodynamic forces induced by seaway and current. The passive self-aligning capability is shown in an integrated simulation for various current velocities and wind-current offset angles.
Assessment of extreme stresses and deflections on wind turbine blades with stochastic material properties using statistical extrapolation methods
Authors: Schinas P N , Serafeim G P , Manolas D I , Riziotis V A , Voutsinas S G , Philippidis T P , Chaviaropoulos P K 
Published: September 2020

Abstract
Since the introduction of the 3rd edition of the IEC Standard 61400-1, designers of wind turbines are required to apply statistical extrapolation techniques, to estimate the extreme (ultimate) load values corresponding to fifty-year return period. In the present paper, the certification procedure is assessed under the uncertainty of the material properties using simulated load time series of the NREL 5MW Reference Wind Turbine. The uncertainty of the material properties is introduced in the elastic properties of the composite blades by using input data from the OptiDAT composite material database. Comparison of the estimated extreme loads and deflections of the blades as well as maximum stresses, also in connection to the Tsai Wu failure criterion, is performed for different material sets. It is found that the variability of the material properties does not affect the estimated ultimate flapwise moments (difference <1.5%) but affects the maximum flapwise deflection (differences ∼8%). It is concluded that for the levels of variation considered in the composite material properties, the coefficient of variation of the extreme stresses and the Tsai Wu failure criterion are in the order of 2% and 8% respectively.
Estimation of roughness effects on wind turbine blades with vortex generators
Authors: Ravishankara A K , Bakhmet I , Özdemir H 
Published: September 2020

Abstract
Surface degradation of the wind turbine blades lead to a reduction while on the other hand blade add-ons like, vortex generators, lead to an increase in the aerodynamic performance. Within this study, both the reduction due to leading edge roughness and the increase due to vortex generators in the aerodynamic performance are quantified individually first, and then it is investigated if the vortex generators would compensate for the losses due to roughness. Roughness models for the Spalart-Allamaras (SA) and k — ω SST turbulence models are implemented in the open source CFD suite SU2 and validated against theoretical predictions and experimental data. The roughness model is then applied to a commonly used airfoil section, DU97-W-300 and steady RANS simulations are carried out with SU2. Four different conditions are considered-no erosion (clean), eroded (rough), clean blade section with VGs and rough blade section with VGs. Numerical simulations are validated with experimental data for the clean airfoil section and airfoil section equipped with vortex generators. Finally, a preliminary analysis is presented for each of the cases considered on the effect of power production.
Impact of Carrier Position and Surrounding Stiffness on Planet Carrier Bearing Loads
Authors: Krause A , Gnauert J , Jacobs G , Bosse D 
Published: September 2020

Abstract
Bearing failures in wind turbine gearboxes still occur which results in downtimes of wind turbines and hence increase the levelized costs of energy. One of these affected bearings is the generator sided planet carrier bearing as it is still subject to unexpected fatigue related failure modes. To reduce the occurrence of these failures a methodology is presented to determine the most influencing wind loads on this planet carrier bearing using the finite element method. Therefore a 1 MW wind turbine drive train model is used and the influence of several parameters influencing the load distribution of the bearing are investigated. These parameters are the surrounding stiffness of the bearing seat, the influence of the individual components of the wind loads and the circumferential position of the planet carrier. The results show that a realistic surrounding of the bearing seat leads to an unequal circumferential load distribution while the bearing itself is less loaded than using the generic surrounding of the bearing seat. The different components of the wind loads do not have much impact on the load distribution while the force acting on the rollers change. The different positions of the planet carrier also do not affect the circumferential load distribution.
The 3D effects of a vertical-axis wind turbine: rotor and wake induction
Authors: Tavernier D. De , Ferreira C. , Paulsen U. , Madsen H. 
Published: September 2020

Abstract
This paper deals with the 3D effects of a vertical-axis wind turbine caused by the tip vortices. In this study, the VAWT rotor is simplified by the infinitely bladed actuator cylinder concept. The loads are prescribed to be uniform and normal to the surface and are distributed between the upwind and downwind half. Depending on the load configuration, the tip vortices are shed at different locations. This causes the wake induction field and the induction at the rotor to be significantly different. The 3D effects cause a power loss that may go up to 15% depending on the load configuration and aspect ratio. Starting from an aspect ratio of 5, the rotor induction and power is approaching 2D results.
Comparison of the free vortex wake and actuator line methods to study the loads of a wind turbine in imposed surge motion
Authors: Corniglion Rèmi , Harris Jeffrey , Peyrard Christophe , Capaldo Matteo 
Published: September 2020

AbstractTo enable the development of floating offshore wind farms, it is important to have a clear understanding of the aerodyamic forces applied on a floating offshore wind turbine. The paper presents comparisons between a lifting line free vortex wake method and an actuator line method in the case of a wind turbine in surge with blade-resolved CFD data as a reference. Each model is compared to a quasi-steady estimation of the loads to understand the variations due to the surge movement. The near-wake flow field is investigated in order to give an insight into the flow features leading to the observed behavior. Both methods predict a higher axial velocity at the position of the rotor and one radius downstream of the rotor in surge conditions compared to the fixed case.
Experimental Comparison of the Wake of a Vertical Axis Wind Turbine and Planar Actuator Surfaces
Authors: Huang M , Ferreira C , Sciacchitano A , Scarano F 
Published: September 2020

Abstract
Wind tunnel experiments on a scaled vertical axis wind turbine (VAWT) and square porous plate with a porosity of 64% are conducted in the W-tunnel of TU-Delft. The VAWT thrusts in axial and lateral directions are measured with an in-house load cell system based on moment conservation. Wake of the VAWT in tip speed ratio of 1.5 and 2.5 and the porous plate is measured with the robotic particle image velocimetry technique, which enables a three-dimensional velocity measurement in a combined volume encompassing from 1 diameter upstream to 3 diameters downstream. Counter-rotating vortex pairs in VAWT wake and the wake shape deformation and deflection are discussed, which are related to the lateral thrust. A square porous plate inducing a similar axial thrust is compared, which has the same shape as the cross-section of the VAWT. Wake of the right porous plate with a yaw angle of 15° is investigated, which produces similar deflection as the VAWT.
Unsteady effects on a pitching airfoil at conditions relevant for large vertical axis wind turbines
Authors: Brunner C E , Kiefer J , Hansen MOL , Hultmark M 
Published: September 2020

Abstract
Interest in offshore vertical axis wind turbines (VAWTs) has created a need to study VAWTs at much higher Reynolds numbers than they have previously been studied at. VAWTs are characterised by unsteady aerodynamics, and high Reynolds numbers have the potential to alter the blade aerodynamics significantly. Here, results are reported on an airfoil that is pitched sinusoidally around zero angle of attack at Rec = 1 × 106, at a reduced frequency k = 0.15 and amplitudes of 5° < α < 20°. Since the static stall angle is not exceeded, no stall effects occur. Nevertheless, lift, drag and moment coefficients show noticeable hysteresis. Despite the high amplitudes of oscillation, lift and moment coefficients show reasonable agreement with unsteady aerodynamic theories by Theodorsen and Motta et al. with regard to the width of the hysteresis loops, but have noticeably steeper slopes.
Numerical Estimation of Anti-icing Heating Power for NREL 5MW Wind Turbine Blades in Cold Climate
Authors: Yassin Khaled , Stoevesandt Bernhard , Peinke Joachim 
Published: September 2020

Abstract
This work aims to give an estimate of to heating power used in the anti-icing system of the NREL 5MW wind turbine rotor operating in a cold climate in the presence of suspended water particles in the air. In this work, the turbine blade was simulated using an in-house code implemented in OpenFOAM framework that uses compressible Lagrange-Euler approach to simulate water particles transport from the atmosphere to the blade surface. On the water film side, Shallow-Water Icing Model (SWIM) is used to simulate the icing and anti-icing process. The results show that at least 3% of the rated power of the rotor should be used just to keep the water film from freezing. It shows also that most of the heating power should be concentrated on the leading edge, lower surface of the blade, and the middle sections of the blade.
Comparative analysis of offshore support structures for two-bladed large wind turbines (10+MW) in deep waters
Authors: Vergassola Marco , Cabboi Alessandro , der Male Pim van 
Published: September 2020

Abstract
The offshore wind market is developing towards exploiting wind resources in deeper water sites. Inevitably, this fuels new research and feasibility studies on alternative solutions for the wind turbine support structures. Within this context, this work aims at comparing three different support structure design concepts for a 14 MW two-bladed downwind wind turbine: an XXL monopile, a hybrid jacket-tower and a lattice tower. To ensure a fair comparability of the three design concepts, a load capacity analysis is first performed to assess the yield strength of each concept and guarantee a similar material utilization. The comparative analysis is then carried out in terms of total mass, dynamic behaviour of the interaction between rotor and support structure, soil-structure interaction and resulting hydrodynamic forces. Based on the given design constraints, the preliminary results of this study favour a lattice tower solution. The study also highlights peculiar dynamic phenomena such as veering, mode hybridization and mode coalescence for the dynamic interaction between the lattice tower and the two-bladed rotor which need to be taken into account during the design phase.
Investigation of flutter for large, highly flexible wind turbine blades
Authors: Kelley C L , Paquette J 
Published: September 2020

Abstract
Improvements to the Sandia blade aeroelastic stability tool have been implemented to predict flutter for large, highly flexible wind turbine blade designs. The aerodynamic lift and moment caused by harmonic edge-wise motion are now included, but did not change the flutter solution, even for highly flexible blades. Flutter analysis of future, large blade designs is presented based on scaling trends. The analysis shows that flutter speed decreases at a rate similar to maximum rotor speed for increasing blade sizes:

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l
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t
t
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t
e
d

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. This indicates the flutter margin is not directly affected by blade length. Rather, it was innovative design technology choices that predicted flutter in previous studies. A 100 m blade, flexible enough to be rail transported, was analyzed and it exhibited soft flutter below rated rotor speed. This indicated that excessive fatigue damage may occur due to limit cycle oscillations for blades that incorporate highly flexible designs.
Uncertainty Quantification of Leading Edge Erosion Impacts on Wind Turbine Performance
Authors: Maniaci David C. , Westergaard Carsten , Hsieh Alan , Paquette Joshua A. 
Published: September 2020

Abstract
Many factors that influence the effect of leading edge erosion on annual energy production are uncertain, such as the time to initiation, damage growth rate, the blade design, operational conditions, and atmospheric conditions. In this work, we explore how the uncertain parameters that drive leading edge erosion impact wind turbine power performance using a combination of uncertainty quantification and wind turbine modelling tools, at both low and medium fidelity. Results will include the predicted effect of erosion on several example wind plant sites for representative ranges of wind turbine designs, with a goal of helping wind plant operators better decide mitigation strategies.