bluuebunny/crossref_metadata_2025_split huggingface dataset:
An innovative segmented blade concept with a partial pitch control for large wind turbine systems
Authors: Kim Taeseong , Hou Lio Alan Wai , Lee Gyeong Han , Choi Dong Kuk , Lee Soo Yong 
Published: June 2024

Abstract
This study investigates the feasibility of a segmented blade with a partial pitch concept. Three different cases were considered where the pitch bearing is positioned at 33%R, 50%R and 66%R, respectively. The PI controller is used with different controller gains corresponding to the blade design. Wind step case and DLC1.1 are applied to analyse its performances. From the wind step case, general controller behaviours and wind turbine responses are investigated. From DLC1.1, the statistics and ultimate loads are studied. From this study, it could be concluded that the segmented blade with a partial pitch could benefit to maintain power without increasing extra loads too much.
How does the blade element momentum method see swept or prebent blades?
Authors: Li Ang , Gaunaa Mac , Pirrung Georg Raimund , Lønbæk Kenneth 
Published: June 2024

Abstract
The blade element momentum (BEM) method is among the mostly used engineering aerodynamic models for wind turbine rotors. Even though the BEM method is strictly only applicable to straight blades forming a planar rotor, it is in practice used for load calculation and design optimization of blades with relatively large sweep, prebend or coning. The present work aims to answer the question: How does the BEM method see swept or prebent blades? The blade element part of the method can be adapted for swept or prebent blades by projecting the velocity and loads between the 2-D airfoil section and the 3-D blade geometry under the cross-flow principle. However, momentum theory considers the 3-D wake and the induction of a planar actuator disc with straight blades. There could be significant differences between the results calculated from different implementations of the BEM method, while the details of the implementations are often omitted in the literature. In the present work, a consistent implementation including the definition of airfoil section alignments and the coordinate systems is provided. It is shown that for a given circulation distribution, the BEM method will predict approximately the same local aerodynamic loads for non-straight blades as if the blades were straight and the rotor was planar. This means using the BEM method to perform aerodynamic optimization of modern rotors with curved blades and/or rotors that are not planar can only have little meaningful result. In order to model the impact of the wake geometry on the induction, more advanced models that take into account the wake geometry on the induction are necessary.
An aeroelastic coupling of an actuator sector model with OpenFAST in atmospheric flows
Authors: Mohammadi Mohammad Mehdi , Chanprasert Warit , Olivares-Espinosa Hugo , Ivanell Stefan 
Published: June 2024

Abstract
This study presents an implementation of an aeroelastically coupled actuator sector model with OpenFAST in a neutral atmospheric boundary layer flow for a 15 MW reference turbine. Three structural cases with different levels of fidelity are considered. In addition, the results from an aeroelastic actuator line model are used for comparison. The results of the structural cases show the significance of including the torsional deflections and structural nonlinearities to accurately calculate the blade loads as it reduces the power and flapwise damage equivalent load values considerably. In terms of the wake flow, there are differences in the near wake between the considered structural cases. Despite this, further downstream the differences become non-significant. In addition, the results from the actuator sector model are in agreement with those obtained from the actuator line model while using the actuator sector model offers a reduction of around 55% to 80% in the computational time depending on the used structural solver.
Moving control surfaces in a geometry-resolved CFD model of an airborne wind energy system
Authors: Pynaert Niels , Haas Thomas , Wauters Jolan , Crevecoeur Guillaume , Degroote Joris 
Published: June 2024

Abstract
Properly understanding the unsteady interaction of the wind with the aircraft is critical to develop reliable airborne wind energy (AWE) systems. High-fidelity simulation tools are needed to accurately predict these interactions, providing insights into the design and operation of efficient and safe AWE systems. In this work, we present a computational fluid dynamics (CFD) framework of an airborne wind system which resolves all lifting surfaces and includes moving control surfaces. This work considers a reference multi-megawatt ground-gen pumping system. To simulate complex fluid flow problems, with large rigid-body motion and deflecting control surfaces using CFD, we opt for the Chimera/overset technique. The goal of this contribution is to demonstrate the effect of the control surfaces in the CFD framework. This work is a major milestone in the ongoing development of high-fidelity aero-servo-elastic simulation models for airborne wind energy systems.
Numerical investigation of vortex-induced forces on a wind turbine tower segment at very high Reynolds numbers
Authors: Ebstrup K , Sørensen N N , Bertagnolio F , Grinderslev C , Horcas S G 
Published: June 2024

Abstract
The vortex-induced forces on an extruded cylinder with a span of two diameters representative of a finite segment of a non-tapered wind turbine tower at a very high Reynolds number (Re = 8.0×106) are numerically investigated using an incompressible Navier-Stokes flow solver with an Improved Delayed Detached Eddy Simulation (IDDES) turbulence model and correlation-based boundary layer transition modelling. The solution shows spanwise correlated structured vortex shedding with the Strouhal number St = 0.48. The boundary layer transition is found to occur at θ
transition = 70
◦
, and boundary layer separation is found to occur at θ
separation = 120
◦
. Results from the grid dependency study strongly imply that when using IDDES, the Strouhal number converges to higher values than previously reported by the literature as the grid is refined, with results ranging from St ∼ 0.44 using a grid with 4.2 × 106 cells, to St = 0.48 for the finest considered grid with 33 × 106 cells. This behaviour is not seen for URANS, where St = 0.33 for the finest grid.
Aerodynamic and Structural Assessment of Floating Wind Turbine Rotor Under Varying Tilt Angle
Authors: Mian H H , Siddiqui M S , Franchina N , Kouaissah O , Wang G , Nygaard T A 
Published: June 2024

Abstract
Predicting the aerodynamic performance of floating offshore wind turbines (FOWTs) proves challenging due to platform motion induced by waves. The effect of wind and waves results in a six-degree-of-freedom motion of the platform, directly influencing turbine performance. Understanding the impact of specific degrees of freedom (DOF) motions on aerodynamics and structural response is crucial for effective wind turbine design. This research examines the impact of rotor tilt on both aerodynamic performance and structural response. The investigation employs computational fluid dynamics (CFD) analysis and mapping aerodynamic loads onto the finite element (FE) mesh for structural analysis. The study employs a comprehensive 3D simulation, utilizing the moving reference frame (MRF) method for the NREL 5 MW reference wind turbine CFD simulations. It explores different rotor tilt angles (5°, 10°, 15°, and 20°) encountered by offshore structures during their operation and examines their impact on aerodynamic performance. Predicted aerodynamic loads were mapped onto the blade FE mesh using the radial basis function (RBF) interpolation technique and solved using the open-source FE solver CalculiX. The analysis shows that the turbine performance is relatively unaffected up to a tilt angle of 10°. However, further increase in rotor tilt angle adversely impacts turbine performance, leading to notable reductions in thrust and power output. The fluid-structure coupled analysis provided insights into the deformations and stresses experienced by the turbine blade, indicating a notable increase in flap-wise displacement for larger tilt angles, while edge-wise displacement is not as significantly affected. The maximum stress location on the blade generally correlates well with actual observations.
Floating wind turbine stability and time response analysis with rotating modes
Authors: Pamfil Bogdan , Bredmose Henrik , Kim Taeseong 
Published: June 2024

Abstract
The periodic azimuthal time dependence of a linearized simple floating wind turbine model with four degrees of freedom is dealt with by developing a particular procedure that enables a stability analysis calculation and reduces computational efforts to calculate time responses. We apply Hill’s method for the aeroelastic stability analysis by generating a constant state-space hyper-matrix that takes into account the periodic azimuthal dependence of the system. It is used to compute precisely the time domain response and to solve an overall eigenvalue problem where natural frequency and modal damping are determined through the eigenvalues. For a varying rotational speed with a fixed air density, eigenfrequencies from Hill’s method are displayed on a Campbell diagram that is based on a waterfall plot of the frequencies obtained by decay tests peaks using the time domain model. Through the modal analysis as well, an investigation of the impact of aerodynamic damping is done following the same procedures by rather fixing the rotational speed and varying air density. In the end, a forcing moment of the platform pitch motion is added to analyze the accuracy of fast time response calculations compared to the time domain model benchmark results.
Multi-fidelity, steady-state aeroelastic modelling of a 22-megawatt wind turbine
Authors: Zahle Frederik , Li Ang , Lønbæk Kenneth , Sørensen Niels N. , Riva Riccardo 
Published: June 2024

Abstract
In this work we present multi-fidelity steady-state aeroelastic framework that leverages the state-of-the-art simulation tool HAWC2 for the structural model, and a variety of aerodynamic models, comprising of the low fidelity blade element momentum (BEM) method, the medium fidelity blade element vortex cylinder (BEVC) method and the coupled near wake and vortex cylinder method, and finally the high-fidelity CFD solver EllipSys3D. The aeroelastic framework is part of AESOpt, an aerostructural framework for design of wind turbine blades. The different aerodynamic models are applied to compute the aeroelastic steady state of the newly designed IEA 22 MW Reference Wind Turbine. The results show a very good agreement between the medium- and high-fidelity aerodynamic models with a maximum of 2.7% difference between the high-fidelity aeroelastic response and that of the lower fidelities.
Edgewise Structural Damping of a 2.8-MW Land-Based Wind Turbine Rotor Blade
Authors: Chetan Mayank , Bortolotti Pietro 
Published: June 2024

Abstract
Modern wind turbines push the predictive capabilities of state-of-the-art aero-servo-elastic tools. The existing limitations hide across the numerical tool chain and can result in serious issues, such as missing aeroelastic instabilities during the design phase. Structural damping is an input that is usually hard to estimate, but also has a major impact on the turbine behavior. In this paper, we discuss an experiment that aims to accurately quantify the structural damping characterizing the edgewise modes of modern wind turbine blades. The experiment is carried out on a 2.8-MW land-based wind turbine and features a fast yaw actuation that induces an edgewise motion on one of the three blades. The Covariant-subspace system identification (Cov-SSI) method is then used to post-process the blade root moment to estimate the short-term edgewise structural damping. Despite limitations of the Cov-SSI method, which consistently under-predicts the absolute values of damping, we observe that structural damping decreases across the first three blade edgewise modes, which is different from the stiffness-proportional damping model that assumes that structural damping increases with the modes. This paper argues that a stiffness-proportional damping model, which is implemented in most aeroelastic tools, is therefore not conservative and might hide aeroelastic instabilities that can instead appear in the field.
Mitigating blade erosion damage through nowcast-driven erosion-safe mode control
Authors: Barfknecht N , Imhoff R , Von Terzi D 
Published: June 2024

Abstract
The erosion-safe mode (ESM) is a novel mitigation strategy that reduces rainfall-induced erosion damage by lowering the tip-speed of the turbine during precipitation events. The ESM requires accurate information about future expected rainfall for its control. In current research, it is debated what method or source should be used to this end. This study explores the effectiveness of driving the ESM using a state-of-the-art weather-radar-based probabilistic rainfall nowcast provided by the Royal Netherlands Meteorological Institute (KNMI). The performance of the nowcast is assessed for various lead times with an impingement-based damage model for three sample sites in the Netherlands and for two distinct ESM strategies. The results show that the quality of the nowcast degrades with increasing lead times, where the 5- and 15-minute lead times exhibit sufficiently good accuracy and response time for adjusting turbine speeds. Overall, the results highlight that the probabilistic information in the nowcast can be employed to improve the efficiency and viability of the ESM.
Optimization of curtailment intervals of wind turbines through assessment of measured loads during start-up and shutdown events
Authors: Ziegler Lisa , Schulze Andreas , Henning Michael 
Published: June 2024

Abstract
There is an increasing amount of curtailment of wind parks due to grid overload or negative market prices. Operators need to also account for the effect of curtailment on component loads, wear, and lifetime. This paper investigates curtailment leading to turbine shutdown. A novel methodology to optimize the length of curtailment intervals based on load neutrality is introduced. Measurement data from the structural health monitoring system of an onshore and an offshore wind turbine are used to quantify effects of curtailment on loads and wear of tower, blade, and pitch system. Shutdown and start-up events increase loads on the tower and pitch system. Blades benefit from lower edgewise loads and reduced erosion. Results show that load neutrality for the tower is reached on average after 63 min of idling for the onshore and after 200 min for the offshore wind turbine evaluated (not generalizable). An optimal curtailment strategy shall use flexible time intervals but ensure load neutrality on yearly average. This can serve as a simple and valuable guideline for wind farm operators to evaluate the criticality of curtailment times in terms of asset fatigue life. Future research shall investigate curtailment strategies that also include deration of power output.
A Virtual Actuator for Advanced Individual Pitch Control (IPC)
Authors: Hovgaard T. G. , Caponetti F. , Grunnet J. D. 
Published: June 2024

Abstract
We present a virtual actuator concept for wind turbine control, wherein rotor force and moment references from various controllers are optimally combined to compute individual blade pitch angles. The approach aims to minimize pitch bearing wear, too. The combined references can come from known control algorithms such as speed regulation, tilt-yaw control, tower dampening and helical wake control [3]. We formulate this as an optimization problem which we solve in an MPC fashion, however, instead of the usual prediction horizon over time, we use a discretized azimuth map as our finite horizon. Serving as a unified interface for all control features utilizing individual pitching, the virtual actuator replaces the plethora of multi-blade transformations and gain-scheduling functions in traditional IPC with one coherent function. Users can directly prioritize features and input constraints on actuators and structural loads. Notably, upstream control algorithms provide rotor force or moment references rather than pitch references. Simulations showcase the virtual actuator’s ability to compute intricate pitch trajectories, surpassing the capabilities of conventional IPC methods. Our method yields novel individual pitching which optimally merges conflicting IPC objectives while minimizing actuator wear.
Automatic Detection and Intensity Classification of Pitch Misalignment of Wind Turbine Blades: a Learning-based Approach
Authors: Milani Sabrina , Leoni Jessica , Cacciola Stefano , Croce Alessandro , Tanelli Mara 
Published: June 2024

Abstract
In recent years, monitoring wind turbine operations, especially in offshore and remote installations, has become crucial. System failures, challenging assessments, and costly maintenance operations are notable concerns. Blade pitch misalignment poses one of the most significant threats, being a leading cause of downtime and energy production reduction. Traditional assessments through frequent inspections are resource-intensive and time-consuming; still they are frequently required as turbines lack routine implementation of effective automatic detection systems.
To address this, our study introduces a novel machine learning-based method for autonomous pitch misalignment recognition, which relies on signals measured by a limited set of sensors, already integrated into modern wind turbines. From those signals, frequency domain features derived by harmonic analysis are extracted, ensuring robust detection also in turbulent wind conditions.
This innovative method lays the groundwork for early and precise wind turbine diagnostics, promoting the shift from time-based to condition-based inspections. This transition aims to reduce maintenance costs and unexpected downtime, ultimately enhancing energy production.
Enhanced Modeling of Joint Yaw and Axial Induction Control Using Blade Element Momentum Methods
Authors: Liew Jaime , Heck Kirby , Howland Michael F. 
Published: June 2024

Abstract
Wind turbine control via concurrent yaw misalignment and axial induction control has demonstrated potential for improving wind farm power output and mitigating structural loads. However, the complex aerodynamic interplay between these two effects requires deeper investigation. This study presents a modified blade element momentum (BEM) model that matches rotor-averaged quantities to an actuator disk model of yawed rotor induction, enabling analysis of joint yaw-induction control using realistic turbine control inputs. The BEM approach reveals that common torque control strategies such as K − Ω2 exhibit sub-optimal performance under yawed conditions. Notably, the power-yaw and thrust-yaw sensitivities vary significantly depending on the chosen control strategy, contrary to common modeling assumptions. In the context of wind farm control, employing induction control which minimizes the thrust coefficient proves most effective at reducing wake strength for a given power output across all yaw angles. Results indicate that while yaw control deflects wakes effectively, induction control more directly influences wake velocity magnitude, underscoring their complementary effects. This study advances a fundamental understanding of turbine aerodynamic responses in yawed operation and sets the stage for modeling joint yaw and induction control in wind farms.
Comparison of helix and wake steering control for varying turbine spacing and wind direction
Authors: Taschner E , Becker M , Verzijlbergh Remco , Van Wingerden JW 
Published: June 2024

Abstract
A variety of wind farm control strategies exist in order to reduce unfavorable wake effects in large wind farms. While strategies like wake steering already reached a high maturity level, it is interesting to compare them to more recently proposed strategies. Such a comparison can form the basis for the development of a symbiotic wind farm control toolbox, from which a control strategy is chosen and activated depending on the operating conditions. The present study compares wake steering with helix control across a wide range of turbine spacings and wind directions using large-eddy simulation (LES). The size of the search space is made computationally tractable for LES by adopting a setup based on one physical upstream turbine and a distribution of virtual downstream turbines which do not exert any thrust force. It is found that helix control is beneficial for full wake overlap and turbine spacing of less than six rotor diameters whereas wake steering proves to be optimal further downstream and for partial wake overlap. Furthermore, the results show that the helix control setpoint in the proximity of full wake overlap scenarios is less susceptible to wind direction variations. This finding indicates that the combination of wake steering and helix control has potential for the design of a wind farm controller which is more robust in full wake overlap scenarios and can reduce the need for large yaw offset adjustments.
Closed-loop coupling of a dynamic wake model with a wind inflow estimator
Authors: Di Cave J , Braunbehrens R , Krause J , Guilloré A , Bottasso C L 
Published: June 2024

Abstract
The estimation of turbine flow evolution provided by low-fidelity dynamic wake models, such as FLORIDyn, can be improved by the introduction of a Kalman filter based on power production measurements. However, it is not possible to infer any information about which side of an impinged rotor is affected by the wake only by the observed power, being itself a single scalar quantity. In this paper, a new closed-loop formulation of the FLORIDyn model is investigated: wind speed estimates, given by a blade load-based wind observer, are implemented into a Kalman Filter, providing information about the position of the wake over the rotor plane. The FLORIDyn model augmented with the wind flow estimator is tested in a layout of two aligned turbines and compared to a corresponding CFD simulation. The results of the proposed approach show an improved ability to predict wind flow quantities and the wake centerline position compared to the open-loop version of the model.