Articles | Volume 7, issue 2
15 Mar 2022
Research article | 15 Mar 2022
Local correlation-based transition models for high-Reynolds-number wind-turbine airfoils
Yong Su Jung et al.
No articles found.
Paul Veers, Carlo Bottasso, Lance Manuel, Jonathan Naughton, Lucy Pao, Joshua Paquette, Amy Robertson, Michael Robinson, Shreyas Ananthan, Athanasios Barlas, Alessandro Bianchini, Henrik Bredmose, Sergio González Horcas, Jonathan Keller, Helge Aagaard Madsen, James Manwell, Patrick Moriarty, Stephen Nolet, and Jennifer Rinker
Wind Energ. Sci. Discuss.,
Preprint under review for WESShort summary
Critical unknowns in the design, manufacturing, and operability of future turbine and plant systems are articulated and recommendations for research action are laid out.
Jeffrey D. Mirocha, Matthew J. Churchfield, Domingo Muñoz-Esparza, Raj K. Rai, Yan Feng, Branko Kosović, Sue Ellen Haupt, Barbara Brown, Brandon L. Ennis, Caroline Draxl, Javier Sanz Rodrigo, William J. Shaw, Larry K. Berg, Patrick J. Moriarty, Rodman R. Linn, Veerabhadra R. Kotamarthi, Ramesh Balakrishnan, Joel W. Cline, Michael C. Robinson, and Shreyas Ananthan
Wind Energ. Sci., 3, 589–613,Short summary
This paper validates the use of idealized large-eddy simulations with periodic lateral boundary conditions to provide boundary-layer flow quantities of interest for wind energy applications. Sensitivities to model formulation, forcing parameter values, and grid configurations were also examined, both to ascertain the robustness of the technique and to characterize inherent uncertainties, as required for the evaluation of more general wind plant flow simulation approaches under development.
Paul Fleming, Jennifer Annoni, Jigar J. Shah, Linpeng Wang, Shreyas Ananthan, Zhijun Zhang, Kyle Hutchings, Peng Wang, Weiguo Chen, and Lin Chen
Wind Energ. Sci., 2, 229–239,Short summary
In this paper, a field test of wake-steering control is presented. In the campaign, an array of turbines within an operating commercial offshore wind farm have the normal yaw controller modified to implement wake steering according to a yaw control strategy. Results indicate that, within the certainty afforded by the data, the wake-steering controller was successful in increasing power capture.
Related subject area
Aerodynamics and hydrodynamicsExperimental investigation of mini Gurney flaps in combination with vortex generators for improved wind turbine blade performanceParked and operating load analysis in the aerodynamic design of multi-megawatt-scale floating vertical-axis wind turbinesHigh-Reynolds-number wind turbine blade equipped with root spoilers – Part 1: Unsteady aerodynamic analysis using URANS simulationsVortex identification methods applied to wind turbine tip vorticesExperimental study of the effect of a slat on the aerodynamic performance of a thick base airfoilDynamic inflow model for a floating horizontal axis wind turbine in surge motionA multipurpose lifting-line flow solver for arbitrary wind energy conceptsA computationally efficient engineering aerodynamic model for swept wind turbine bladesA computationally efficient engineering aerodynamic model for non-planar wind turbine rotorsSome effects of flow expansion on the aerodynamics of horizontal-axis wind turbinesExperimental analysis of radially resolved dynamic inflow effects due to pitch stepsFLOWERS: An integral approach to engineering wake modelsWind tunnel testing of a swept tip shape and comparison with multi-fidelity aerodynamic simulationsDucted wind turbines in yawed flow: a numerical studyUNAFLOW: a holistic wind tunnel experiment about the aerodynamic response of floating wind turbines under imposed surge motionVertical-axis wind-turbine computations using a 2D hybrid wake actuator-cylinder modelMaximal power per device area of a ducted turbineHow realistic are the wakes of scaled wind turbine models?Response of the International Energy Agency (IEA) Wind 15 MW WindCrete and Activefloat floating wind turbines to wind and second-order wavesA simplified model for transition prediction applicable to wind-turbine rotorsHigh Reynolds investigations on the ability of the full scale e-TellTale sensor to detect flow separation on a wind turbine blade sectionExperimental investigation of wind turbine wake and load dynamics during yaw maneuversThe curled wake model: a three-dimensional and extremely fast steady-state wake solver for wind plant flowsSurrogate-based aeroelastic design optimization of tip extensions on a modern 10 MW wind turbineLow-Reynolds-number investigations on the ability of the strip of e-TellTale sensor to detect the flow features over wind turbine blade section: flow stall and reattachment dynamicsPressure-based lift estimation and its application to feedforward load control employing trailing-edge flapsAn impulse-based derivation of the Kutta–Joukowsky equation for wind turbine thrustField test of an active flap system on a full-scale wind turbineDetermination of the angle of attack on a research wind turbine rotor blade using surface pressure measurementsAerodynamic effects of Gurney flaps on the rotor blades of a research wind turbineIdentification of airfoil polars from uncertain experimental measurementsLaminar-turbulent transition characteristics of a 3-D wind turbine rotor blade based on experiments and computationsParametric slat design study for thick-base airfoils at high Reynolds numbersAn improved second-order dynamic stall model for wind turbine airfoilsThe flow past a flatback airfoil with flow control devices: benchmarking numerical simulations against wind tunnel dataOn the velocity at wind turbine and propeller actuator discsCartographing dynamic stall with machine learningTop-level rotor optimisations based on actuator disc theoryTwo-dimensional numerical simulations of vortex-induced vibrations for a cylinder in conditions representative of wind turbine towersValidation and accommodation of vortex wake codes for wind turbine design load calculationsImproving wind farm flow models by learning from operational dataActuator line simulations of wind turbine wakes using the lattice Boltzmann methodDevelopment of a second-order dynamic stall modelInvestigations of aerodynamic drag forces during structural blade testing using high-fidelity fluid–structure interactionBrief communication: A fast vortex-based smearing correction for the actuator lineBrief communication: A double-Gaussian wake modelThe effect of wind direction shear on turbine performance in a wind farm in central IowaImplementation of the blade element momentum model on a polar grid and its aeroelastic load impactBrief communication: Wind-speed-independent actuator disk control for faster annual energy production calculations of wind farms using computational fluid dynamicsPerformance study of the QuLAF pre-design model for a 10 MW floating wind turbine
Jörg Alber, Marinos Manolesos, Guido Weinzierl-Dlugosch, Johannes Fischer, Alexander Schönmeier, Christian Navid Nayeri, Christian Oliver Paschereit, Joachim Twele, Jens Fortmann, Pier Francesco Melani, and Alessandro Bianchini
Wind Energ. Sci., 7, 943–965,Short summary
This paper investigates the potentials and the limitations of mini Gurney flaps and their combination with vortex generators for improved rotor blade performance of wind turbines. These small passive add-ons are installed in order to increase the annual energy production by mitigating the effects of both early separation toward the root region and surface erosion toward the tip region of the blade. As such, this study contributes to the reliable and long-term generation of renewable energy.
Mohammad Sadman Sakib and D. Todd Griffith
Wind Energ. Sci., 7, 677–696,Short summary
This paper presents a comprehensive aerodynamic design study for a 5 MW Darrieus offshore VAWT in the context of multi-megawatt floating VAWTs. This study systematically analyzes the effect of different, important design variables including the number of blades, aspect ratio and blade chord tapering in a comprehensive load analysis of both the parked and operating aerodynamic loads including turbine power performance analysis using a vortex-based aerodynamic model.
Thomas Potentier, Emmanuel Guilmineau, Arthur Finez, Colin Le Bourdat, and Caroline Braud
Wind Energ. Sci., 7, 647–657,Short summary
The spoiler is found to efficiently rearrange the mean flow seen by thick aerofoil: adding lift throughout the positive angles of attack, the drawback is a high drag penalty coupled with high unsteadiness of the aerodynamic forces. The impact of this type of excitation will be quantified further in terms of energy production and fatigue in future work.
Rodrigo Soto-Valle, Stefano Cioni, Sirko Bartholomay, Marinos Manolesos, Christian Navid Nayeri, Alessandro Bianchini, and Christian Oliver Paschereit
Wind Energ. Sci., 7, 585–602,Short summary
This paper compares different vortex identification methods to evaluate their suitability to study the tip vortices of a wind turbine. The assessment is done through experimental data from the wake of a wind turbine model. Results show comparability in some aspects as well as significant differences, providing evidence to justify further comparisons. Therefore, this study proves that the selection of the most suitable postprocessing methods of tip vortex data is pivotal to ensure robust results.
Axelle Viré, Bruce LeBlanc, Julia Steiner, and Nando Timmer
Wind Energ. Sci., 7, 573–584,Short summary
There is continuous effort to try and improve the aerodynamic performance of wind turbine blades. This work shows that adding a leading-edge slat to wind turbine blades can significantly enhance the aerodynamic performance of wind turbines, even more than with vortex generators (which are commonly used on commercial turbines). The findings are obtained through wind tunnel tests on different airfoil–slat combinations.
Carlos Ferreira, Wei Yu, Arianna Sala, and Axelle Viré
Wind Energ. Sci., 7, 469–485,Short summary
Floating offshore wind turbines may experience large surge motions that, when faster than the local wind speed, cause rotor–wake interaction. We derive a model which is able to predict the wind speed at the wind turbine, even for large and fast motions and load variations in the wind turbine. The proposed dynamic inflow model includes an adaptation for highly loaded flow, and it is accurate and simple enough to be easily implemented in most blade element momentum design models.
Emmanuel Branlard, Ian Brownstein, Benjamin Strom, Jason Jonkman, Scott Dana, and Edward Ian Baring-Gould
Wind Energ. Sci., 7, 455–467,Short summary
In this work, we present an aerodynamic tool that can model an arbitrary collections of wings, blades, rotors, and towers. With these functionalities, the tool can be used to study and design advanced wind energy concepts, such as horizontal-axis wind turbines, vertical-axis wind turbines, kites, or multi-rotors. This article describes the key features of the tool and presents multiple applications. Field measurements of horizontal- and vertical-axis wind turbines are used for comparison.
Ang Li, Georg Raimund Pirrung, Mac Gaunaa, Helge Aagaard Madsen, and Sergio González Horcas
Wind Energ. Sci., 7, 129–160,Short summary
An engineering aerodynamic model for the swept horizontal-axis wind turbine blades is proposed. It uses a combination of analytical results and engineering approximations. The performance of the model is comparable with heavier high-fidelity models but has similarly low computational cost as currently used low-fidelity models. The model could be used for an efficient and accurate load calculation of swept wind turbine blades and could eventually be integrated in a design optimization framework.
Ang Li, Mac Gaunaa, Georg Raimund Pirrung, and Sergio González Horcas
Wind Energ. Sci., 7, 75–104,Short summary
An engineering aerodynamic model for non-planar horizontal-axis wind turbines is proposed. The performance of the model is comparable with high-fidelity models but has similarly low computational cost as currently used low-fidelity models, which do not have the capability to model non-planar rotors. The developed model could be used for an efficient and accurate load calculation of non-planar wind turbines and eventually be integrated in a design optimization framework.
David H. Wood and Eric J. Limacher
Wind Energ. Sci., 6, 1413–1425,Short summary
The airflow through a wind turbine must expand as it goes through the blades for them to extract energy from the wind. Expansion has not been properly incorporated in wind turbine aerodynamics. We show that the conventional equation for wind turbine thrust becomes inaccurate when the expansion is maximized to achieve maximum power, and expansion reduces power by around 6 %. We formulate equations for the disturbance of the external flow and show that this is maximized at the rotor plane.
Frederik Berger, David Onnen, Gerard Schepers, and Martin Kühn
Wind Energ. Sci., 6, 1341–1361,Short summary
Dynamic inflow denotes the unsteady aerodynamic response to fast changes in rotor loading and leads to load overshoots. We performed a pitch step experiment with MoWiTO 1.8 in the large wind tunnel of ForWind – University of Oldenburg. We measured axial and tangential inductions with a recent method with a 2D-LDA system and performed load and wake measurements. These radius-resolved measurements allow for new insights into the dynamic inflow phenomenon.
Michael LoCascio, Christopher Bay, Majid Bastankhah, Garrett Barter, Paul Fleming, and Luis Martínez-Tossas
Wind Energ. Sci. Discuss.,
Revised manuscript accepted for WESShort summary
This work introduces the FLOW Estimation and Rose Superposition (FLOWERS) wind turbine wake model. This model analytically integrates the wake over wind directions to provide a time-averaged flow field. This new formulation is used to perform layout optimization. The FLOWERS model provides a smooth flow field over an entire wind plant at fraction of the computational cost of the standard numerical integration approach.
Thanasis Barlas, Georg Raimund Pirrung, Néstor Ramos-García, Sergio González Horcas, Robert Flemming Mikkelsen, Anders Smærup Olsen, and Mac Gaunaa
Wind Energ. Sci., 6, 1311–1324,Short summary
Curved blade tips can potentially have a significant impact on wind turbine performance and loads. A swept tip shape optimized for wind turbine applications is tested in a wind tunnel. A range of numerical aerodynamic simulation tools with various levels of fidelity are compared. We show that all numerical tools except for the simplest blade element momentum based are in good agreement with the measurements, suggesting the required level of model fidelity necessary for the design of such tips.
Vinit Dighe, Dhruv Suri, Francesco Avallone, and Gerard van Bussel
Wind Energ. Sci., 6, 1263–1275,Short summary
Ducted wind turbines (DWTs) can be used for energy harvesting in urban areas where non-uniform flows are caused by the presence of buildings or other surface discontinuities. For this reason, the aerodynamic performance of DWTs in yawed-flow conditions must be characterized. It is found that the duct cross-section camber offers not only insensitivity to yaw but also a gain in performance up to a specific yaw angle; thereafter any further increase in yaw results in a performance drop.
Alessandro Fontanella, Ilmas Bayati, Robert Mikkelsen, Marco Belloli, and Alberto Zasso
Wind Energ. Sci., 6, 1169–1190,Short summary
The scale model wind tunnel experiment presented in this paper investigated the aerodynamic response of a floating turbine subjected to imposed surge motion. The problem is studied under different aspects, from airfoil aerodynamics to wake, in a coherent manner. Results show quasi-static behavior for reduced frequencies lower than 0.5 and possible unsteadiness for higher surge motion frequencies. Data are made available to the public for future verification and calibration of numerical models.
Edgar Martinez-Ojeda, Francisco Javier Solorio Ordaz, and Mihir Sen
Wind Energ. Sci., 6, 1061–1077,Short summary
A model for computing vertical-axis wind turbine farms was developed using computational fluid dynamics open-source software. This model has the potential of evaluating wind farm configurations which can lead to a higher annual energy yield. Such configurations have not been studied thoroughly due to the fact that most analysis tools are computationally expensive. This model can also be run in personal computers within a matter of minutes or hours depending on the number of turbines.
Nojan Bagheri-Sadeghi, Brian T. Helenbrook, and Kenneth D. Visser
Wind Energ. Sci., 6, 1031–1041,Short summary
The design of a ducted wind turbine was optimized to maximize the power per total cross-sectional area of the device. The associated power coefficient was 0.70, which is significantly greater than that obtainable from an open rotor turbine. Furthermore, it was shown that there is an optimal duct length, which is 15 % of the rotor diameter.
Chengyu Wang, Filippo Campagnolo, Helena Canet, Daniel J. Barreiro, and Carlo L. Bottasso
Wind Energ. Sci., 6, 961–981,Short summary
This paper quantifies the fidelity of the wakes generated by a small (1 m diameter) scaled wind turbine model operated in a large boundary layer wind tunnel. A detailed scaling analysis accompanied by large-eddy simulations shows that these wakes are very realistic scaled versions of the ones generated by the parent full-scale wind turbine in the field.
Mohammad Youssef Mahfouz, Climent Molins, Pau Trubat, Sergio Hernández, Fernando Vigara, Antonio Pegalajar-Jurado, Henrik Bredmose, and Mohammad Salari
Wind Energ. Sci., 6, 867–883,Short summary
This paper introduces the numerical models of two 15 MW floating offshore wind turbines (FOWTs) WindCrete and Activefloat. WindCrete is a spar floating platform designed by Universitat Politècnica de Catalunya, while Activefloat is a semi-submersible platform designed by Esteyco. The floaters are designed within the Horizon 2020 project COREWIND. Later in the paper, the responses of both models to wind and second-order waves are analysed with an emphasis on the effect of second-order waves.
Thales Fava, Mikaela Lokatt, Niels Sørensen, Frederik Zahle, Ardeshir Hanifi, and Dan Henningson
Wind Energ. Sci., 6, 715–736,Short summary
This work develops a simplified framework to predict transition to turbulence on wind-turbine blades. The model is based on the boundary-layer and parabolized stability equations, including rotation and three-dimensionality effects. We show that these effects may promote transition through highly oblique Tollmien–Schlichting (TS) or crossflow modes at low radii, and they should be considered for a correct transition prediction. At high radii, transition tends to occur through 2D TS modes.
Antoine Soulier, Caroline Braud, Dimitri Voisin, and Danbon Frédéric
Wind Energ. Sci. Discuss.,
Revised manuscript accepted for WESShort summary
The e-Telltale, a new aerodynamic sensor have been tested in a large wind tunnel in the CSTB. This sensor have been designed to detect the flow separation on wind turbine blades which can cause energy production losses and increased aging of the blades. Theses wind tunnel tests higlighted the good ability of the e-Telltale to detect the flow separation and the influence of the size and location of the e-Telltale on the flow separation detection.
Stefano Macrí, Sandrine Aubrun, Annie Leroy, and Nicolas Girard
Wind Energ. Sci., 6, 585–599,Short summary
This paper investigates the effect of misaligning a wind turbine on its wake deviation response and on the global load variation of a downstream wind turbine during a positive and negative yaw maneuver, representing a misalignment–realignment scenario. Yaw maneuvers could be used to voluntarily misalign wind turbines when wake steering control is targeted. The aim of this wind farm control strategy is to optimize the overall production of the wind farm and its lifetime.
Luis A. Martínez-Tossas, Jennifer King, Eliot Quon, Christopher J. Bay, Rafael Mudafort, Nicholas Hamilton, Michael F. Howland, and Paul A. Fleming
Wind Energ. Sci., 6, 555–570,Short summary
In this paper a three-dimensional steady-state solver for flow through a wind farm is developed and validated. The computational cost of the solver is on the order of seconds for large wind farms. The model is validated using high-fidelity simulations and SCADA.
Thanasis Barlas, Néstor Ramos-García, Georg Raimund Pirrung, and Sergio González Horcas
Wind Energ. Sci., 6, 491–504,Short summary
A method to design advanced tip extensions for modern wind turbine blades is presented in this work. The resulting design concept has high potential in terms of actual implementation in a real rotor upscaling with a potential business case in reducing the cost of energy produced by future large wind turbine rotors.
Antoine Soulier, Caroline Braud, Dimitri Voisin, and Bérengère Podvin
Wind Energ. Sci., 6, 409–426,Short summary
Monitoring the flow features over wind turbine blades is a challenging task that has become more and more crucial to monitor and/or operate wind turbine blades. This paper demonstrates the ability of an innovative sensor to detect these features over wind turbine blades. The spatiotemporal description of the flow over the surface has been measured over an oscillating blade section and the strip displacement was compared, showing the ability of the sensor to detect stall.
Sirko Bartholomay, Tom T. B. Wester, Sebastian Perez-Becker, Simon Konze, Christian Menzel, Michael Hölling, Axel Spickenheuer, Joachim Peinke, Christian N. Nayeri, Christian Oliver Paschereit, and Kilian Oberleithner
Wind Energ. Sci., 6, 221–245,Short summary
This paper presents two methods on how to estimate the lift force that is created by a wing. These methods were experimentally assessed in a wind tunnel. Furthermore, an active trailing-edge flap, as seen on airplanes for example, is used to alleviate fluctuating loads that are created within the employed wind tunnel. Thereby, an active flow control device that can potentially serve on wind turbines to lower fatigue or lower the material used for the blades is examined.
Eric J. Limacher and David H. Wood
Wind Energ. Sci., 6, 191–201,Short summary
This paper describes a new analysis of wind turbine thrust based on removing pressure from the equations for the wind flow through a wind turbine rotor. We show that the equation is free from the effects of flow expansion that must accompany the slowing down of the wind through the blades as they extract the kinetic energy. The conditions under which the assumptions are used in blade-element analysis, which is fundamental for wind turbine aerodynamics, are made clear for the first time.
Alejandro Gomez Gonzalez, Peder B. Enevoldsen, Athanasios Barlas, and Helge A. Madsen
Wind Energ. Sci., 6, 33–43,Short summary
This work describes a series of tests of active flaps on a 4 MW wind turbine. The measurements were performed between October 2017 and June 2019 using two different active flap configurations on a blade of the turbine, showing a potential to manipulate the loading of the turbine between 5 % and 10 %. This project is performed with the aim of demonstrating a technology with the potential of reducing the levelized cost of energy for wind power.
Rodrigo Soto-Valle, Sirko Bartholomay, Jörg Alber, Marinos Manolesos, Christian Navid Nayeri, and Christian Oliver Paschereit
Wind Energ. Sci., 5, 1771–1792,Short summary
In this paper, a method to determine the angle of attack on a wind turbine rotor blade using a chordwise pressure distribution measurement was applied. The approach used a reduced number of pressure tap data located close to the blade leading edge. The results were compared with the measurements from three external probes mounted on the blade at different radial positions and with analytical calculations.
Jörg Alber, Rodrigo Soto-Valle, Marinos Manolesos, Sirko Bartholomay, Christian Navid Nayeri, Marvin Schönlau, Christian Menzel, Christian Oliver Paschereit, Joachim Twele, and Jens Fortmann
Wind Energ. Sci., 5, 1645–1662,Short summary
The aerodynamic impact of Gurney flaps is investigated on the rotor blades of the Berlin Research Turbine. The findings of this research project contribute to performance improvements of different-size rotor blades. Gurney flaps are considered a worthwhile passive flow-control device in order to alleviate the adverse effects of both early separation in the inner blade region and leading-edge erosion throughout large parts of the blade span.
Chengyu Wang, Filippo Campagnolo, and Carlo L. Bottasso
Wind Energ. Sci., 5, 1537–1550,Short summary
A new method is described to identify the aerodynamic characteristics of blade airfoils directly from operational data of the turbine. Improving on a previously published approach, the present method is based on a new maximum likelihood formulation that includes errors both in the outputs and the inputs. The method is demonstrated on the identification of the polars of small-scale turbines for wind tunnel testing.
Özge Sinem Özçakmak, Helge Aagaard Madsen, Niels Nørmark Sørensen, and Jens Nørkær Sørensen
Wind Energ. Sci., 5, 1487–1505,Short summary
Accurate prediction of the laminar-turbulent transition process is critical for design and prediction tools to be used in the industrial design process, particularly for the high Reynolds numbers experienced by modern wind turbines. Laminar-turbulent transition behavior of a wind turbine blade section is investigated in this study by means of field experiments and 3-D computational fluid dynamics (CFD) rotor simulations.
Julia Steiner, Axelle Viré, Francesco Benetti, Nando Timmer, and Richard Dwight
Wind Energ. Sci., 5, 1075–1095,Short summary
The manuscript deals with the aerodynamic design of slat elements for thick-base airfoils at high Reynolds numbers using integral boundary layer and computational fluid dynamics models. The results highlight aerodynamic benefits such as high stall angle, low roughness sensitivity, and higher aerodynamic efficiency than standard single-element configurations. However, this is accompanied by a steep drop in lift post-stall and potentially issues related to the structural design of the blade.
Galih Bangga, Thorsten Lutz, and Matthias Arnold
Wind Energ. Sci., 5, 1037–1058,Short summary
Robust and accurate dynamic stall modeling remains one of the most difficult tasks in wind turbine load calculations despite its long research effort in the past. The present paper describes a new second-order dynamic stall model for wind turbine airfoils. The new model is robust and improves the prediction for the aerodynamic forces and their higher-harmonic effects due to vortex shedding but also provides improved predictions for pitching moment and drag.
George Papadakis and Marinos Manolesos
Wind Energ. Sci., 5, 911–927,Short summary
Flatback airfoils are used in the root region of wind turbine blades since they have several structural and aerodynamic benefits. Several flow control devices are incorporated to mitigate the effects of vortex shedding in the wake of such airfoils. In this work, two different numerical approaches are compared to wind tunnel measurements to assess the suitability of each method for predicting the performance of the flow control devices in terms of loads and unsteady characteristics.
Gijs A. M. van Kuik
Wind Energ. Sci., 5, 855–865,Short summary
The paper compares actuator discs in propeller and wind turbine mode. At very low rotational speed, propeller discs have an expanding wake while still energy is put into the wake. The velocity at the disc in the plane containing the axis is practically uniform: a few per mille deviation for wind turbine discs and a few per cent for propeller discs. The deviations are caused by the different strengths of the singularity in the wake boundary vorticity strength at its leading edge.
Matthew Lennie, Johannes Steenbuck, Bernd R. Noack, and Christian Oliver Paschereit
Wind Energ. Sci., 5, 819–838,Short summary
This study presents a marriage of unsteady aerodynamics and machine learning. When airfoils are subjected to high inflow angles, the flow no longer follows the surface and the flow is said to be separated. In this flow regime, the forces experienced by the airfoil are highly unsteady. This study uses a range of machine learning techniques to extract infomation from test data to help us understand the flow regime and makes recomendations on how to model it.
Wind Energ. Sci., 5, 807–818,Short summary
Wind turbine rotors are usually designed to maximize power performance, accepting any loading results. However, from the most basic wind turbine theory, actuator disc theory, two other optimization paths are demonstrated, which may lead to more cost-effective technology – the low-induction rotor where an expanded rotor diameter and some extra power is achieved without increasing the blade root bending moment and the secondary rotor which can provide a very low torque and low-cost drivetrain.
Axelle Viré, Adriaan Derksen, Mikko Folkersma, and Kumayl Sarwar
Wind Energ. Sci., 5, 793–806,Short summary
Vortex-induced vibrations are structural vibrations that can occur due to the shedding of flow vortices when a fluid flow passes around a structure. Here, conditions specific to wind turbine towers are investigated numerically. The work highlights a complex interplay between structural and fluid dynamics. In particular, certain conditions lead to a continuous alternation between self-exciting and self-limiting vortex-induced vibrations, linked to a change in the sign of the aerodynamic damping.
Koen Boorsma, Florian Wenz, Koert Lindenburg, Mansoor Aman, and Menno Kloosterman
Wind Energ. Sci., 5, 699–719,Short summary
The present publication has contributed towards making vortex wake models ready for application to certification load calculations. The reduction in flapwise blade root moment fatigue loading using vortex wake models instead of the blade element momentum method has been verified using dedicated CFD simulations. A validation effort against a long-term field measurement campaign featuring 2.5 MW turbines has confirmed the improved prediction of unsteady load characteristics by vortex wake models.
Johannes Schreiber, Carlo L. Bottasso, Bastian Salbert, and Filippo Campagnolo
Wind Energ. Sci., 5, 647–673,Short summary
The paper describes a new method that uses standard historical operational data and reconstructs the flow at the rotor disk of each turbine in a wind farm. The method is based on a baseline wind farm flow and wake model, augmented with error terms that are
learnedfrom operational data using an ad hoc system identification approach. Both wind tunnel experiments and real data from a wind farm at a complex terrain site are used to show the capabilities of the new method.
Henrik Asmuth, Hugo Olivares-Espinosa, and Stefan Ivanell
Wind Energ. Sci., 5, 623–645,Short summary
The presented work investigates the potential of the lattice Boltzmann method (LBM) for numerical simulations of wind turbine wakes. The LBM is a rather novel, alternative approach for computational fluid dynamics (CFD) that allows for significantly faster simulations. The study shows that the method provides similar results when compared to classical CFD approaches while only requiring a fraction of the computational demand.
Niels Adema, Menno Kloosterman, and Gerard Schepers
Wind Energ. Sci., 5, 577–590,Short summary
It is crucial to model dynamic stall accurately to reduce inaccuracies in predicting fatigue and extreme loads. This paper investigates a new dynamic stall model. Improvements are proposed based on experiments. The updated model shows significant improvements over the initial model; however, further validation and research are still required. This updated model might be incorporated into future wind turbine design codes and will hopefully reduce inaccuracies in predicted wind turbine loads.
Christian Grinderslev, Federico Belloni, Sergio González Horcas, and Niels Nørmark Sørensen
Wind Energ. Sci., 5, 543–560,Short summary
This study focuses on coupled computational fluid and structural dynamics simulations of a dynamic structural test of a wind turbine blade, as performed in laboratories. It is found that drag coefficients used for simulations, when planning fatigue tests, underestimate air resistance to the dynamic motion that the blade undergoes during tests. If this is not corrected for, this can result in the forces applied to the blade actually being lower in reality during tests than what was planned.
Alexander R. Meyer Forsting, Georg R. Pirrung, and Néstor Ramos-García
Wind Energ. Sci., 5, 349–353,Short summary
Simulations of wind farms allow the estimation of the forces acting on the turbines and thus their lifetime and power production. Representing the actual geometric shape of turbines in a realistic atmospheric flow is computationally expensive; therefore they are modelled in a simplified manner. Unfortunately, these simplifications negatively impact the estimated forces. We developed an open-source aerodynamic model that corrects the forces, giving more accurate estimates of lifetime and power.
Johannes Schreiber, Amr Balbaa, and Carlo L. Bottasso
Wind Energ. Sci., 5, 237–244,Short summary
An analytical wake model with a double-Gaussian velocity distribution is used to improve on a similar formulation by Keane et al (2016). The choice of a double-Gaussian shape function is motivated by the behavior of the near-wake region that is observed in numerical simulations and experimental measurements. The model is calibrated and validated using large eddy simulations replicating scaled wind turbine experiments, yielding improved results with respect to a classical single-Gaussian profile.
Miguel Sanchez Gomez and Julie K. Lundquist
Wind Energ. Sci., 5, 125–139,Short summary
Wind turbine performance depends on various atmospheric conditions. We quantified the effect of the change in wind direction and speed with height (direction and speed wind shear) on turbine power at a wind farm in Iowa. Turbine performance was affected during large direction shear and small speed shear conditions and favored for the opposite scenarios. These effects make direction shear significant when analyzing the influence of different atmospheric variables on turbine operation.
Helge Aagaard Madsen, Torben Juul Larsen, Georg Raimund Pirrung, Ang Li, and Frederik Zahle
Wind Energ. Sci., 5, 1–27,Short summary
We show in the paper that the upscaling of turbines has led to new requirements in simulation of the unsteady aerodynamic forces by the engineering blade element momentum (BEM) model, originally developed for simulation of the aerodynamics of propellers and helicopters. We present a new implementation of the BEM model on a polar grid which can be characterized as an engineering actuator disc model. The aeroelastic load impact of the new BEM implementation is analyzed and quantified.
Maarten Paul van der Laan, Søren Juhl Andersen, and Pierre-Elouan Réthoré
Wind Energ. Sci., 4, 645–651,Short summary
Wind farm layouts are designed by simple engineering wake models, which are fast to compute but also include a high uncertainty. Higher-fidelity models, such as Reynolds-averaged Navier–Stokes, can be used to verify optimized wind farm layouts, although the computational costs are high due to the large number of cases that are needed to calculate the annual energy production. This article presents a new wind turbine control method to speed up the high-fidelity simulations by a factor of 2–3.
Freddy J. Madsen, Antonio Pegalajar-Jurado, and Henrik Bredmose
Wind Energ. Sci., 4, 527–547,Short summary
This paper presents a comparison study of the simplified model QuLAF (Quick Load Analysis of Floating wind turbines) and FAST for the planar version of various design load cases, in order to investigate how accurate results can be obtained from this simplified model. The overall analysis shows that QuLAF is generally very good at estimating the bending moment at the tower base and the floater motions, whereas the nacelle acceleration is generally underpredicted.
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In RANS CFD, the eN-based method showed its superiority over local correlation-based transition models (LCTMs) coupled with the SST turbulence model for predicting transition behavior at high-Reynolds-number flows (3–15 million). We evaluated the performance of two LCTMs coupled with the SA turbulence model. As a result, the SA-based two-equation transition model showed a comparable performance with the eN-based method and better glide ratio (L/D) predictions than the SST-based model.
In RANS CFD, the eN-based method showed its superiority over local correlation-based transition...