bluuebunny/crossref_metadata_2025_split huggingface dataset:
Power Maximization and Fatigue-Load Mitigation in a Wind-turbine Array by Active Yaw Control: an LES Study
Authors: Lin Mou , Porté-Agel Fernando 
Published: September 2020

Abstract
In this study, we perform a multi-objective parametric study for an array of three miniature wind turbines subjected to active yaw control (AYC), with the objectives of maximizing the power and minimizing the fatigue loads. Using the time series extracted from large-eddy simulation (LES), we compute the mean power and the yaw-moment damage equivalent load (DEL) at every point of a finite decision space spanned by the yaw angles of the first two turbines. The mean power outputs simulated with LES are compared with those measured in the wind tunnel, and a good agreement is found between the two. The Pareto front of different yaw configurations is extracted in the objective space of AYC and the Pareto-optimal strategies are identified in the decision space. We find that most of the Pareto-optimal strategies share the characteristic of moderately decremental yaw angles. We also find that the strategies with a small yaw angle for the first wind turbine are inefficient since they incur significant increases in fatigue while only achieving marginal power gains. The results indicate that the decision space of algorithms searching for optimal AYC strategies can be significantly reduced a priori with the consideration of load mitigation in the optimization.
Optimization of Wind Farm Design for Objectives Beyond LCOE
Authors: Dykes Katherine 
Published: September 2020

Abstract
For wind farms that participate actively in electricity markets versus receiving a fixed kiloWatt-hour payment, design and operational objectives must go beyond the levelized cost of energy (LCOE) to account for system value and profitability of the farm over its lifetime. This work introduces ”beyond LCOE” objectives for farm design and illustrates their impact in a multi-objective optimization case study for LCOE and value-based objectives. The case study shows that the best designs from an LCOE perspective are not those that have the highest value and vice versa. Thus, designing wind farms in the future will require new optimization approaches to address the broader system and market context to ensure overall profitability of the project.
Innovative rail transport of a supersized land-based wind turbine blade
Authors: Carron William Scott , Bortolotti Pietro 
Published: September 2020

Abstract
Wind turbine blade logistic providers are being challenged with escalating costs and routing complexities as one-piece blade approach lengths of 75 m in various regions of the U.S. land-based market. New lower cost solutions are needed to enable further reductions in the levelized cost of energy (LCOE) and continued market expansion. In this paper, a novel method of using existing U.S. rail infrastructure to deploy 100-m, one-piece blades to U.S. land-based wind sites is numerically investigated. The study removes the constraint that blades must be kept rigid during transport, and it allows bending to keep blades within a clearance profile while navigating horizontal and vertical curvatures. Novel system optimization and blade design processes consider blade structural constraints and rail logistic constraints in parallel to develop a highly flexible, rail-transportable blade. Results indicate maximum deployment potential in the Interior region of the United States and limited deployment potential in other regions. The study concludes that innovative rail transportation solutions combined with advanced rotor technologies can provide a feasible alternative to segmentation and support continued LCOE reductions in the U.S. land-based wind energy market.
Generalised grid requirements minimizing the actuator line angle-of-attack error
Authors: Forsting AR Meyer , Troldborg N 
Published: September 2020

AbstractThe actuator line (AL) is a lifting line (LL) representation of aerodynamic surfaces in computational fluid dynamics (CFD) applications. The AL blade forces are computed from 2D airfoil polars and the CFD velocity vector extracted at the line position, as the self-induction at the very centre of the bound vortex should, following vortex theory, be nil. Yet, this is not the case in CFD, which leads to errors in the angle-of-attack computation. We derive an expression for the error in the lift force from vortex considerations and show it to be a function of chord, the smearing length scale used in distributing the AL forces over the numerical domain and the number of grid cells per smearing length scale. Thereby demonstrating that the required number of grid cells-contrary to current belief-needs to grow faster than the inverse of the smearing length scale refinement to maintain the error level. We additionally show that the error can be large for the commonly used ratio of 2 grid cells per length scale, especially if the latter is relatively small with respect to the rotor radius. Ultimately, the recommendation is to always run with the largest smearing length scale possible for the specific application in conjunction with a smearing correction, as this minimizes the error in the blade forces whilst reducing the computational resources required.
Practical Considerations on Wind Turbine Blade Leading Edge Erosion Modelling and its Impact on Performance and Loads
Authors: Papi F , Ferrara G , Bianchini A 
Published: September 2020

Abstract
Wind turbines operate in all sorts of weather conditions around the globe, exploiting installation sites with high power production potential. These machines operate within the atmospheric boundary layer and are therefore subject to impacts with rain, hail dust particles and insects, often leading to rapid blade deterioration and performance drops. This wok aims to explore different ways of modelling wind turbine blade leading edge erosion with a medium-fidelity approach and to show how different models impact performance and loads. This provides a quick way of evaluating the effects of blade deterioration. A 2D airfoil erosion model is developed and lift and drag coefficients are calculated with Computational Fluid Dynamics (CFD). An aero-servo-elastic model of the DTU 10MW Reference Wind Turbine (RWT) is then used to evaluate the impacts of the models on performance. Differences in airfoil performance are discussed as well as differences in the turbine’s power coefficient and fatigue loading levels.
Off-axis loading in rotor blade fatigue tests with elliptical biaxial resonant excitation
Authors: Melcher David , Petersen Enno , Neßlinger Sebastian 
Published: September 2020

Abstract
In their lifetime of 20-25 years, wind turbine rotor blades are subjected to high-cycle fatigue. Hence, new rotor blade designs need to undergo cyclic fatigue tests to show that they fulfill the reliability requirements. For these tests, a blade prototype is loaded consecutively in its flapwise and lead-lag directions, which does not represent the actual loading in the field very well. This applies especially for the off-axis load directions of the blade, i.e., the load directions between flapwise and lead-lag directions. By combining the two consecutive tests into one biaxial test, these loads can be improved. Exciting both directions at the same time also generates loads in the off-axis directions.
This work investigates the loading of a biaxial fatigue test using elliptical biaxial resonant excitation. By changing the phase angle of the elliptical excitation, the loading of the blade can be altered to better represent the operational conditions of the blade.
Consolidated results of the laboratory and full scale field validation of an active flap system
Authors: Gonzalez A. Gomez , Enevoldsen P. , Barlas T.K. , Madsen H.Aa , Olsen A. S. 
Published: September 2020

Abstract
This article presents the consolidated results of a comprehensive validation campaign of a pneumatic active flap system (AFS) developed within the scope of the Induflap2 project [1] in a collaboration effort between Siemens Gamesa Renewable Energy A/S (SGRE), the Technical University of Denmark (DTU), and Rehau GmbH. The validation results presented herein include wind tunnel measurements, measurements in a rotating test rig under free atmospheric conditions, as well as the validation at full scale on a 4MW wind turbine with 130m rotor diameter (SWT-4.0-130). This article is of a summarizing character and the reader is referred to further literature where applicable. During the course of the project, several revisions of the AFS were developed and tested at different levels of fidelity. Along with the different variations of the AFS, the impact of variations of the geometric and material related design parameters were studied. Two of the latest revisions of the AFS were tested at full scale on a wind turbine. The measurements presented herein focus solely on the latest revision of the AFS (internally referred to as the FT008rev10 concept). The different tests and measurements were performed in the period from 2016 to 2019. During the full scale measurements, a wind speed dependent load impact between 5% and 10% was measured for the blade root flapwise bending moments, demonstrating thus a large potential for turbine loading adjustments to perform active load control on modern wind turbines.
Experimental Demonstration of Thrust Vectoring with a Vertical Axis Wind Turbine using Normal Load Measurements
Authors: Leblanc Bruce , Ferreira Carlos 
Published: September 2020

Abstract
The aerodynamic loading of a vertical axis wind turbine varies with the azimuth position of the blades. The thrust of the VAWT can be computed as a decomposition of the normal force on each of the blades. By varying the blade loading as a function of turbine azimuth, it is possible to vary the direction of the average thrust of the turbine. An experiment is performed using an active pitch controlled H-VAWT turbine in the Open Jet Facility at TU Delft demonstrating the ability to actively vary the rotor aerodynamic loading and as a result the average thrust vector. By applying a sinusoidal pitch actuation with phase offsets, a directional change in the average thrust vector of over 78° was demonstrated.
Comparison of 3D aerodynamic models for vertical-axis wind turbines: H-rotor and Φ-rotor
Authors: Tavernier D. De , Sakib M. , Griffith T. , Pirrung G. , Paulsen U. , Madsen H. , Keijer W. , Ferreira C. 
Published: September 2020

Abstract
Since the first commercial projects, the development of vertical-axis wind turbines (VAWTs) has been impeded by the limited understanding and inability to accurately model VAWTs. This paper investigates and compares different aerodynamic modelling techniques for VAWTs in 3D. All considered models are using the same blade-element characteristics but use different descriptions to determine the induced velocity field. The H-and Φ-rotor are studied with various aspect ratios and rotor loadings. Both instantaneous azimuthal parameters as well as integral parameters, such as the thrust and power are investigated. The paper concludes that capturing the 3D effects of VAWTs is challenging and the trends to be expected are not straightforward due to the complex vortex system created by VAWTs. All model assumptions affect the results both at the mid-plane of the rotor as well as at the blade tips.
Direct numerical simulation of transitional boundary layers on a horizontal axis wind turbine blade
Authors: Jing Z , Ducoin A , Braud C 
Published: September 2020

Abstract
In boundary layer flow around rotating machines, a radial (or cross-flow) velocity exists due to Coriolis and centrifugal forces. This velocity component can be of great importance for laminar-turbulent transition. A series of direct numerical simulations (DNS) are performed to study the boundary layer flow transition on a rotating Horizontal Axis Wind Turbine blade. To quantify the effect of blade rotation, results are compared with that from airfoil DNS, where the section is taken from 3D blades and does not rotate. It is shown that the rotation gives rise to a small radial velocity and slightly modifies the shape of unstable waves. However, the transition location and mechanism of 3D blade boundary layer flow resemble 2D flow for the investigated case.
Reduced order models for wind turbine blades with large deflections
Authors: Gözcü Ozan , Dou Suguang 
Published: September 2020

Abstract
Non-intrusive nonlinear reduced order modeling (ROM) techniques have been applied by researchers to obtain computationally cheap and yet accurate structural responses of aircraft panels. However, its application to wind turbine blades is new and challenging due to much larger deflections of wind turbine blades. This study improves a non-intrusive nonlinear ROM method for wind turbine blades going through large deflections. In the nonlinear ROM, the nonlinear stiffness is described by the quadratic and cubic functions, and the secondary motions induced by the primary large deflections are described by the modal derivative vectors in the reduction basis. The non-intrusive nature of the method requires a geometrically nonlinear solver, and HAWC2 is chosen in this study for the computation of nonlinear stiffness terms. Two examples, including a cantilever beam example and the NREL 5MW wind turbine blade model, are used to evaluate the accuracy and computational effectiveness of the nonlinear ROMs. The cantilever beam example shows that the nonlinear ROM can accurately capture the axial displacements due to large deflections reaching 20 % of span length as well as the torsion coupled with flapwise and edgewise motions. The NREL blade example shows that the nonlinear ROM is accurate for the tip displacements more than 5.9 m. Because the size of the nonlinear ROM is much smaller than that of HAWC2 model, a speedup factor of 8.5 for computational time is observed for the NREL blade example.
CFD modeling of the Poul la Cour Tunnel
Authors: Sørensen Niels N. , Olsen A. S. , Bak C. , Gaunaa M. , Beckerlee J.S. , Fischer A. , Mikkelsen R.F. , Ildvedsen S. 
Published: September 2020

Abstract
We analyze the new Danish Poul la Cour Tunnel (PLCT) facility using 2D and 3D Computation Fluid Dynamics simulations, with the aim to address the need for wind tunnel corrections. The assessment of tunnel corrections is based on 2D free simulations representing undisturbed airfoil flow, 2D tunnel configurations and a full 3D tunnel setup using laminar/turbulent Improved Delayed Dettached Eddy Simulations. By comparing lift, drag and pressure distributions and detailled flow patterns, the influence of the 2D and 3D tunnel is evaluated. In the present study a NACA 633-418 airfoil is investigated in the tunnel.
Comparison of loads from HAWC2 and OpenFAST for the IEA Wind 15 MW Reference Wind Turbine
Authors: Rinker Jennifer , Gaertner Evan , Zahle Frederik , Skrzypiński Witold , Abbas Nikhar , Bredmose Henrik , Barter Garrett , Dykes Katherine 
Published: September 2020

Abstract
Reference wind turbines (RWTs) that reflect the state-of-the-art of current wind energy technology are necessary in order to properly evaluate innovative methods in wind turbine design and evaluation. The International Energy Agency (IEA) Wind Technology Collaboration Platform (TCP) Task 37 has recently developed a new RWT geared towards offshore floating-foundation applications: the IEA Wind 15 MW. The model has been implemented in two aeroelastic codes, OpenFAST and HAWC2, based on an underlying common ontology. However, these toolchains result in slightly different structural parameters, and the two codes utilise different structural models. Thus, to increase the utility of the model, it is necessary to compare the aeroelastic responses. This paper compares aeroelastic loads calculated using different fidelities of the blade model in OpenFAST (ElastoDyn and BeamDyn) and HAWC2 (prismatic Timoshenko without torsion and Timoshenko with fully populated stiffness matrix), where both codes use the DTU Basic controller and the same turbulence boxes to reduce discrepancies. The aeroelastic responses to steady wind, step wind and turbulent wind (per IEC 61400-1 wind class IB) are considered. The results indicate a generally good agreement between the loads dominated by aerodynamic thrust and force, especially for the no-torsion blade models. Discrepancies were observed in other load channels, partially due to differences in the asymmetric loading of the rotor and partially due to differing closed-loop dynamics, and they will be the subject of future investigations.
Uncertainty in loads for different constraint patterns in constrained-turbulence generation
Authors: Rinker Jennifer M. 
Published: September 2020

Abstract
This paper investigates the effect that adding constraints to turbulence simulations has on the uncertainty of resulting aeroelastic loads. The constrained turbulence is generated using the open-source constrained turbulence generator PyConTurb (“Python Constrained Turbulence”). A selection of constraint patterns were used to mimic the design of a met mast layout; i.e., the number of sonic anemometers and their locations throughout the rotor. A case study is presented to demonstrate in detail the effects of adding constraints before a larger numerical experiment is presented. The results of the numerical experiment indicate that adding constraints is extremely beneficial in reducing the mean absolute error of both operational parameters and loads. The reduction in mean absolute error ranged from 13% to 98%. The error in the extreme values and damage-equivalent loads were not impacted by the added constraints due to lack of gusts in the original signals and the similarity of the power spectra of the constrained and non-constrained signals, respectively.
A DNN surrogate unsteady aerodynamic model for wind turbine loads calculations
Authors: Ananthan Shreyas , Vijayakumar Ganesh , Yellapantula Shashank 
Published: September 2020

Abstract
A recurrent deep-neural network (DNN) surrogate model capable of modeling the unsteady aerodynamic response and dynamic stall behavior of wind turbine blades has been developed and validated for use in engineering design codes. The model is trained using a subset of the oscillating airfoil experiments conducted at the Ohio State University wind tunnel. The predictions from our DNN model show excellent agreement with the measured data and, in all cases, a marked improvement over the state-of-the-art unsteady aerodynamic models. The DNN-based unsteady aerodynamics model was integrated with OpenFAST to perform full-turbine load computations for the NREL-5MW rotor. The largest differences are observed for the inboard stations, particularly in the pitching moment response, when using the new surrogate model compared to the other models available in OpenFAST.
CFD Simulation of Two Tandem Floating Offshore Wind Turbines in Surge Motion
Authors: Rezaeiha Abdolrahim , Micallef Daniel 
Published: September 2020

Abstract
High-fidelity unsteady Reynolds-averaged Navier-Stokes (URANS) CFD simulation is employed to investigate the variations in the power performance of two tandem in-line floating offshore horizontal axis wind turbines for the scenario in which the upstream rotor is oscillating in surge motion and the downstream rotor is positioned in a distance of 3D (D: turbine diameter) and is stationary. The rotors are the NREL-5MW reference turbine. The platform surge period and wave amplitude are 9 s and 1.02 m, respectively. The results are presented for 100 full surge periods. It is found that the surge motion of the upstream rotor results in: (i) sinusoidal fluctuations in the power and thrust coefficients (CP
and C
T) of the upstream rotor with a standard deviation (std) of 9.7% and 5.5%, respectively; (ii) such fluctuations in CP
and CT
are less regular with a std of 4.2% and 2.8% for the downstream rotor, respectively. A low-frequency oscillating mode with a period nearly 10 times the surge period is also observed for the downstream rotor. The mean Cp and Ct of the downstream rotor are 28.9% and 38.5% of the upstream one.
Model-based displacement estimation of wind turbine blades using strain modal data
Authors: Gundlach J , Knebusch J , Govers Y , Haller B 
Published: September 2020

Abstract
For wind turbine rotor blades, the use of strain sensors is preferred over acceleration sensors for the purpose of permanent monitoring. Experimental modal analysis during operation is thus constrained to strain information, yielding strain modal data including strain mode shapes. For follow-up investigations such as aerodynamic load assessment or flutter monitoring it is however advantageous to have this information as displacement mode shapes or as displacements of the blade contour over time. This research applies a generic approach that converts strain mode shapes to displacement mode shapes utilizing an FE shell model as a basis for approximation. The accuracy of the approach is assessed by comparison with experimentally identified high-resolution displacement mode shapes which are acquired with accelerometers and serve as a reference. In the process the conversion procedure is illustrated with the help of strain data that has been obtained using a sensor instrumentation installed for certification testing of the blade. The requirements for successful usage of the employed conversion scheme and its suitability for rotor blade data are discussed.
Advances Toward a Lightweight, Variable Fidelity Wake Simulation Tool
Authors: Saverin Joseph , Marten D , Nayeri N , Paschereit CO 
Published: September 2020

Abstract
A method is presented which aims to bridge the gap between overly simplified momentum-based wake models and overly demanding finite volume models of wind turbine wake evolution. The method has been developed to allow an essentially user-defined resolution of the wake. Beyond this, all dominant field quantities are automatically resolved by the solver including convection velocity, shear stress and turbulence intensity. Two distinct methods of solution are presented which both have strengths and weaknesses, the choice of which model being fidelity and application dependent. Both methods make use of multilevel spatial integration to allow greatly improved computational efficiency. The method is here presented for 2D flow in the symmetry plane of a vertical axis wind turbine as an initial demonstration of the potential of the method.
Development of a fluid structure interaction tool based on an actuator line model
Authors: Spyropoulos Nikos , Prospathopoulos John , Manolas Dimitris , Papadakis George , Riziotis Vasilis A 
Published: September 2020

AbstractIn the present paper the methodology and the procedures for the implicit coupling of an Actuator Line (AL) aerodynamic code with a beam like structural code for the analysis of wind turbine rotors are detailed. Results from benchmark aeroelastic simulations of canonical inflow conditions, comparing the newly developed AL model against a standard Blade Element Momentum (BEM) model are presented in the paper. The two models provide very similar results in simple, uniform inflow, axisymmetric flow cases. The advantages of this newly developed tool emerge when more complex inflow conditions are addressed. In the present paper, besides axial flow conditions, operation under high yaw misalignment is also considered. BEM model accounts for the effect of the wake skewness through the application of an a posteriori engineering correction. Therefore, in this particular non symmetric flow case, deviations between AL and BEM are expected to be higher, especially as yaw misalignment angles increase. In the paper the above differences are assessed and interpreted.