bluuebunny/crossref_metadata_2025_split huggingface dataset:
Robust wind farm layout optimization
Authors: Sinner Michael , Fleming Paul 
Published: June 2024

Abstract
Wake interactions in wind farms cause losses in annual energy production (AEP) on the order of 10%. Wind farm designers optimize the layout of the farm to mitigate wake losses, especially in the dominant site-specific wind directions. As wind turbines and wind farms grow in scale, optimization becomes more complex. Offshore wind farms regularly comprise more than 100 wind turbines and are characterized by complex boundaries due to shipping lanes, neighboring wind farms, and other constraints.
Layout optimization methods are broadly split between gradient-based and gradient-free approaches. Gradient-based approaches can converge quickly and perform well for smaller, academic problems but are often sensitive to initial conditions and tuning parameters and require expert knowledge to use. On the other hand, gradient-free approaches can be more robust to problem complexities. We present a robust layout optimization approach based on a random search algorithm. The algorithm is intended for those who are not optimization experts and has few tuning parameters that need specification to achieve satisfactory results. Unlike off-the-shelf methods, which use generally available, non-domain-specific optimization routines that accept as inputs an optimization function and constraint definitions, this approach takes advantage of the relative computational costs of the different evaluations by evaluating cheaper computations first (boundary and minimum distance constraints) and running expensive AEP evaluations only if all other checks pass. Moreover, an outer genetic algorithm allows multiple solutions to evolve in parallel, enabling rapid solution development on high-performance computers. We discuss the relative ease of selecting necessary tuning parameters and demonstrate the efficacy of the genetic random search on a complex layout problem consisting of placing 70 turbines in a nonconvex and unconnected boundary region.
Comparison of 25 MW downwind and upwind turbine designs with individual pitch control
Authors: Phadnis Mandar , Escalera Mendoza Alejandra S. , Jeong Michael , Loth Eric , Todd Griffith D. , Pusch Manuel , Pao Lucy 
Published: June 2024

Abstract
As conventional upwind wind turbines grow larger, the increased mass and flexibility of the longer blades present challenges concerning costs, structural loads, and safety constraints such as tower clearance. At extreme scales, wind turbines in a downwind configuration may provide a feasible alternative to address these challenges by allowing lightweight, flexible blades that can reduce capital costs and blade loads while maintaining safety margins. Downwind turbine blades suffer from increased fatigue loading due to the tower shadow effect. In this study, novel downwind, three-bladed wind turbine designs at 25 MW rating with lightweight, flexible blades are evaluated and compared in terms of power production and structural loading. To obtain a baseline performance, a standard collective blade pitch wind turbine controller is implemented for the two downwind and one upwind turbine designs. Individual pitch control is then added for the downwind turbines to reduce structural fatigue on the turbine blades. In summary, the two downwind turbine designs that differ in rotor pre-coning and shaft tilt angles using collective and individual pitch control are compared against a conventional upwind turbine with collective pitch control at the same scale under turbulent wind conditions.
LES-based validation of a dynamic wind farm flow model under unsteady inflow and yaw misalignment
Authors: Bohrer Jan Kai , Petrović Vlaho , Rott Andreas , Kühn Martin 
Published: June 2024

Abstract
This work presents the validation of an extended version of the control-oriented, dynamic wind farm flow solver SPLINTER. The two-dimensional model is applied to use cases of wake steering by yaw misalignment and inflow wind direction variations and the results are compared to large-eddy simulations (LES). While SPLINTER is able to reproduce the antagonal behaviour of decreasing upstream and increasing downstream turbine power under wake deflection, a systematic deviation of the downstream power is detected and quantified, which is connected to underrepresented three-dimensional wake effects. In case of changing inflow wind direction, SPLINTER is capable of computing movement and shape of the bending wakes. The model smooths small-scale turbulent structures and disturbances and does not reproduce wake meandering, but manages to describe the evolution of the mean flow, which is tested by averaging over an ensemble of LES and comparing the resulting flow fields and turbine power time series. Under dynamic inflow conditions, SPLINTER is able to predict at which time intervals and at which rates downstream turbines will be influenced by wakes, which can improve the accuracy of short-term power and load forecasting and enables its application to online model predictive wind farm control.
Model wind turbine performance in turbulent–non-turbulent boundary layer flow
Authors: Neuhaus Lars , Ribnitzky Daniel , Hölling Michael , Wächter Matthias , Avila Kerstin , Kühn Martin , Peinke Joachim 
Published: June 2024

Abstract
With increasing distance from the coast and greater hub heights, wind turbines expand into unknown, hardly researched environmental conditions. As height increases, laminar flow conditions become more likely. With the simultaneous increase in rotor diameter, very different flow conditions, from laminar to turbulent, occur over the rotor area. It is crucial to understand the effects of these different flow conditions on wind turbines. We approach this through wind tunnel experiments, presenting a setup with two different active grids. This setup enables the generation of four different flows – homogeneous, shear, turbulent–non-turbulent, and turbulent–non-turbulent shear flow – each with four different turbulence levels. The turbulent–non-turbulent flows exhibit a turbulence intensity gradient between the quasi-laminar flow at the upper and turbulent flow at the lower rotor half, establishing a turbulent–non-turbulent interface between the two rotor halves. In a second step, we investigate the Model Wind Turbine Oldenburg with a rotor diameter of 1.8 m (MoWiTO 1.8) under these conditions and analyze their effects on power output and blade loads. While the power fluctuations depend directly on the turbulence intensity, an additional turbulence intensity gradient shows no significant effect. A stronger effect can be observed for the blade root bending moments, the fluctuations of which increase with shear and also in turbulent–non-turbulent flow.
Prediction of rain erosion damage progression using disdrometer rain data: The importance of liquid water content
Authors: Hannesdóttir Ásta , Dellwik Ebba , Hasager Charlotte Bay 
Published: June 2024

Abstract
Wind turbine blade erosion poses a significant challenge to the durability and performance of wind turbines. Modeling of rain erosion damage, considering atmospheric conditions, improves our understanding of the progression of leading-edge erosion on wind turbine blades. In this study, we investigate the impact of varying raindrop characteristics on rain erosion damage development. We analyse 2.5 years of data from a disdrometer, which measures the size and velocity of falling rain droplets, at Risø campus. Various post-processing methods of the disdrometer data are used for estimating representative droplet diameters and fall velocities for each rain event. We compare measured droplet fall velocities with theoretical terminal velocities, revealing a necessity for revising theoretical approaches to raindrop fall velocity for erosion damage modeling. The measured rain rates and representative fall velocities are used to calculate the liquid water content in the air. We introduce a bin-wise summation method for estimating the liquid water content, circumventing the need for representative droplet assumptions. As this method provides the most accurate input for the damage model, we benchmark the other post-processing methods against it and employ it to evaluate bias estimates of associated damage predictions. The largest bias (22%) in accumulated damage is found with an arithmetic mean droplet diameter approach and the smallest bias (-2%) with the median volume estimation method for damage model input. Furthermore, we demonstrate that, for a given rainfall volume, smaller droplets contribute to larger accumulated damage compared to larger droplets.
Measuring wake deflection from SCADA data during wake steering using machine learning
Authors: Post Nathan , Zheng Cheng , Kerrigan Daniel , Bertini Enrico , Tory Melanie 
Published: June 2024

Abstract
As wake steering is implemented on large wind plants, methods for evaluating how well these systems optimize plant performance are needed. The data analysis from experiments conducted so far generally focuses on evaluating the improvement in power or energy production of the plant and comparing that to the predicted improvement. In this study, we explore a new approach to provide additional insight and validation of optimization tools by measuring the wake deflection experimentally using only the downstream turbine as a sensor. This approach is demonstrated using the SMARTEOLE wind plant wake steering experimental data. Light gradient boosting machines (LGBM) and Gaussian process (GP) machine learning models are trained and then interrogated by making a set of predictions under defined conditions to determine the wake deflection observed at the downstream turbine. The data set is sparse, particularly for larger yaw angles, and noisy due to factors not captured in the SCADA leading to relatively high uncertainty in the predictions. The GP model is better suited to smoothly fit this data. Using the GP model, a wake deflection of 0.35 rotor diameters at 3.7 rotor diameters downwind is estimated for a yaw error of 20 degrees on the upwind turbine.
Flow around a pair of 2D cylinders using a hybrid Eulerian-Lagrangian solver
Authors: Pasolari R. , Ferreira C. , Van Zuijlen A. 
Published: June 2024

Abstract
The field of external aerodynamics encompasses various engineering disciplines with a significant impact on wind energy technology. Aerodynamic investigations provide insights not only into the characteristics of individual blades or standalone wind turbines but also into entire wind farms. As advancements in wind turbine design continue, understanding the interactions between turbines in close proximity becomes crucial, presenting a multi-body problem. Researchers require efficient and accurate tools to comprehensively study such dynamics. This paper presents a hybrid Eulerian-Lagrangian solver designed to leverage the strengths of Eulerian solvers in resolving boundary layers and Lagrangian solvers in convecting wakes downstream without introducing significant numerical diffusion. The solver adeptly handles multi-body simulations, allowing the construction of independent Eulerian meshes that communicate seamlessly through Lagrangian particles. In this way, the computational study of multibody problems does not require very large and dense meshes. Validation in single-body cases has already been conducted, with this paper demonstrating the solver’s application to a pair of cylinders in different configurations. A comparative performance analysis is carried out against pure Eulerian solvers. The results highlight that the hybrid solver efficiently reproduces the accuracy of the Eulerian solver, demonstrating its effectiveness in handling complex aerodynamic simulations.
A New Perspective on Offshore Wind Turbine Certification Using High Performance Computing
Authors: Papi Francesco , Bianchini Alessandro 
Published: June 2024

Abstract
A correct estimation of fatigue and ultimate loads on the structure is key for wind turbine design and certification. In a greater perspective, wind turbines are large structures placed in the natural environment and are thus subject to environmental loads that are stochastic in nature. In the case of offshore turbines, the design space is even vaster, as wind speed, turbulence intensity, wave height and period, and wind/wave direction need to be considered. Due to this complexity, standardization is a challenge, and current design standards prescribe load calculations to be performed on a site-per-site basis. Performing this task requires obtaining a long-term statistical representation of the installation site, which can be complex. Moreover, this process is affected by uncertainties. This work explores an alternative to this approach, i.e., partially, or entirely simulating the lifetime of the offshore asset. Results show how this method can reliably predict fatigue loads even using as little as one year of data. On the other hand, prediction of extreme loads is influenced by the sample size and time-period.
Comprehensive analysis of rotor edgewise whirling mode interaction with rotor speed harmonics
Authors: Torres Antonio , Gil Javier , Plaza Aitor , Aginaga Jokin 
Published: June 2024

Abstract
This paper presents a model that investigates the interaction between rotor edgewise whirling modes and rotor speed harmonics in wind turbines. The model is based on kinematic and dynamic principles, with a focus on the multi-blade coordinate transformation, which is critical for simulating the behaviour of the rotor whirling modes in wind turbines. The research has two objectives: to investigate the interaction between the rotor edgewise whirling modes and the rotor speed harmonics, and to provide clearer graphs that explain the complex nature of this non-intuitive rotor dynamics. The paper concludes by highlighting the practical implications of the research findings, in particular the effectiveness of visualisation techniques in identifying and explaining unexpected interactions.
VAST as a generic, modular aeromechanics code for wind turbine simulation
Authors: Michels Benedikt , Seelemeyer Philipp 
Published: June 2024

Abstract
In order to leverage the full potential wind energy, more research is needed both in the field and numerically. At DLR, the need for simulation competencies is expected to be met by the in-house developed generic and highly flexible multi-physics code VAST. While initially aimed at low- to medium-fidelity simulations of helicopter aeromechanics, the code is applicable to other problems like wind turbine computations. The goal of this paper is to present the general concept of VAST and briefly introduce the available physics models. Next to examples of successful application to helicopter simulation problems, first results in the field of wind energy are shown. The well-known IEA 15 MW reference wind turbine is used as a basis to compare VAST — both with a BEMT and a vortex theory inflow model — to other tools with similar and higher-fidelity physics modeling. For the rigid turbine, blade loads are compared with results of other tools using engineering models as well as CFD, showing good overall agreement. A more detailed evaluation of aerodynamic quantities like the angle of attack and the induced velocity field is presented for VAST and the CFD results. An outlook on the ongoing VAST developments is given.
Aeroelastic analysis of a very large wind turbine in various atmospheric stability conditions
Authors: Dangi Nirav , Yu Wei , Sodja Jurij , Ferreira Carlos Simão 
Published: June 2024

Abstract
With the growing trend towards larger wind turbine rotor diameters, the impact of wind shear on rotor performance and loads becomes increasingly significant. Atmospheric stability strongly influences wind shear, leading to higher wind shear under stable atmospheric conditions. In this study, the aeroelastic performance of the IEA 22 MW rotor is assessed under inflow conditions generated by different methods. Inflow conditions were generated using turbulence models specified in the IEC Standards and also by Large Eddy simulations. Standalone OpenFAST simulations were conducted with the respective inflow conditions.
It was found that at rated and above-rated wind speeds, the time-averaged wind turbine design loads were higher in stable atmospheric conditions, in comparison to the IEC NTM inflow conditions, while the opposite held for below-rated wind speeds. Specifically, the time-averaged root flapwise bending moment and rotor thrust were found to be higher by up to 7% in stable atmospheres. However, maximum design and fatigue loads were considerably higher in the IEC NTM case due to elevated turbulence levels. Compared to the IEC NTM case, the damage equivalent root flapwise bending moment was found to be 30% to 70% lower in the different scenarios.
A grid deformation method for wind turbine CFD applications
Authors: Sørensen Niels N. 
Published: June 2024

Abstract
The desire for low cost of energy is driving the development of modern wind turbines toward more and more flexible designs. With respect to aerodynamic evaluation of these designs based on CFD this pose a requirement for the capability to compute the flow on deforming grids around heavily deforming geometries. The present paper describes an efficient explicit method suited for deforming geometries in a structured grid approach, here illustrated for airfoil and a wind turbine rotor simulations. Based on the present investigation, it is illustrated that the solution on the deformed grids deviates less than a fraction of a percent from the solution on the original grids both for the airfoil and the rotor case.
Mesoscale-coupled Large Eddy Simulation for Wind Resource Assessment
Authors: Storey Rupert , Rauffus Rene 
Published: June 2024

Abstract
Turbulence, a key driver of wind turbine loads, is central in the assessment of turbine suitability and performance, and consequently impacts the expected energy production of a wind farm. Conventional flow modeling methods for wind resource assessment (WRA) typically lack the ability to resolve turbulence due to key simplifications in their formulation. This work applies Large Eddy Simulation (LES) to address these limitations and deliver high-fidelity wind condition predictions at 24 wind farm sites. The model includes recently improved boundary conditions to downscale information from global weather models via a mesoscale layer. Validation of the model is presented through comparison to over 100 years of measurements, with comparison of the time-series, distributions and spectra. Validation results indicate excellent performance of the model for key flow quantities including wind speed, turbulence and direction. Comparison of spectra indicates a significant improvement in the representation of the atmospheric energy cascade when compared to previous approaches. The results are significant for wind-farm site assessment as they demonstrate the feasibility of applying accurate LES at a commercial scale. LES also provides a step change in the quality of model predictions through resolving time and site-specific turbulence characteristics. The application of the model for WRA is a step towards improved understanding of the wind resource, as well as an improved suitability assessment process itself.
Accuracy assessment of Beddoes-Leishman and IAG dynamic stall models for wind turbine applications
Authors: Mohamed Omar Sherif , Melani Pier Francesco , Bangga Galih , Aryan Navid , Greco Luca , Bianchini Alessandro 
Published: June 2024

Abstract
The study presents a systematic comparison between two of the most-credited dynamic stall models for wind turbine applications: the original Beddoes-Leishman (BL) model and the newly-developed IAG. The scope of such comparison, supported by experimental data, is to shed new light on the actual suitability of current dynamic stall models for their integration into modern wind turbine simulation codes, and on the best practices to calibrate them. Two different strategies are followed for the calibration of the BL model: 1) standard one, compliant with common practices found in the literature; 2) a physics-oriented one, focusing on the constants defining the dynamic stall onset as well as on the parameters governing the duration of the vortex shedding process. The IAG model, initially developed based on the first-order BL formulation and recently improved by reducing the number of constants and removing compressibility effects, is applied instead in its standard form only. The two models are compared across a range of oscillation mean angles, amplitudes, and reduced frequencies. Results demonstrate that the original BL model, although with a challenging calibration process, when properly tuned, can provide a very good description of aerodynamic unsteady loads. While showing consistent results, the IAG formulation appears to be more robust, as it employs fewer constants and extracts most of the needed information directly from the input polar data. The comparison between the calibrated BL and IAG models highlights critical modelling aspects, the computation of drag and determination of the stall onset above all, offering valuable insights for the future development of dynamic stall formulations.
Techno-economic designs of hybrid wind-wave offshore energy systems and comparison with TOPSIS analysis: an Italian case study
Authors: Petracca E. , Sirigu M. , Issoglio D. , Ghigo A. , Bracco G. 
Published: June 2024

Abstract
This study assesses multiple hybrid wind and wave floating offshore systems, utilizing a preliminary approach for dimensioning and the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) analysis method for comparison. It aims to provide an initial evaluation of diverse concepts, emphasizing state-of-the-art combinations of Floating offshore Wind Turbine (FOWT) with Wave Energy Converters (WECs). The criteria for evaluation include system cost, power extraction, WEC integration, dynamic and environmental responses, offering a comprehensive view of performance, economic viability, constructability, operational efficiency, and environmental impact. The findings, derived from the application of these methodologies, are informed by an Italian case study, enriching the insights and illustrating the practical implications of the evaluated hybrid systems within the Italian context. Preliminary results suggest a tendency for semi-submersible platforms to be more suitable for combined with WEC devices.
Adhesive Snap-Fit Joints for Modular Wind Turbine Blades: A Numerical Feasibility Study
Authors: Ansari Muhammad Basit , Maes Vincent , Macquart Terence , Kim Byung Chul , Pirrera Alberto 
Published: June 2024

Abstract
Larger rotor diameters are sought by wind turbine manufacturers as they favour cost-effective energy generation. However, manufacturing, transporting, and installing longer blades gets increasingly complicated, time-consuming, and costly. While a potential solution lies in spanwise segmentation, available modular blade technologies are still relatively immature, have drawbacks, and are yet to be used for blades exceeding 80 meters. A key challenge to blade segmentation is the addition of joints, which can result in both structural as well as aeroelastic penalties, when comparing segmented designs to their monolithic counterparts. To tackle these issues, in this study, we present the proof of concept and initial feasibility of an adhesively bonded snap-fit joint. The study assesses the joint’s load carrying capacity under quasi-static loading conditions at two levels: first, at the component level, focusing on the snap-fit elements, and second, at the system level, examining the integration of these components into the blade section. Under the specified assumptions, the results highlight the hybrid joint’s capability to withstand substantial loads of the order of magnitude required to meet operating requirements.