bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical study and LiDAR based validation of the wind field in urban sites
Authors: von der Grün M , Zamre P , Chen Y , Lutz T , Voß U , Krämer E 
Published: September 2020

Abstract
Within the project “Windy Cities” the economic use of small wind turbines in urban areas is investigated in Tübingen, Germany. This test-site contains complex terrain, forested areas and various types of buildings making the local wind field more turbulent and complex. To avoid damages and reduced life times of small wind turbines caused by high turbulence a detailed prediction of the wind field is essential in the present study. This is done using CFD.
The scope of this study is the validation of the setup including terrain and vegetation. For this, on-site planar wind field LiDAR data are utilized to define the inflow boundary condition for highly resolved Detached Eddy Simulations (DES) using ANSYS Fluent. The required preprocessing steps of the LiDAR data are explained in detail and their assumptions, which are made to interpolate the data onto the numerical inflow plane. Since the inflow region is covered by forested zones a forest model is introduced with a local tree height adaption based on Laser scan data. LiDAR data, which are measured further downstream, are used to validate the forest model. Simulations with and without the considered forest are compared to investigate the influence of the forested region.
Optimizing a wind farm layout considering access roads
Authors: Roscher B , Mortimer P , Schelenz R , Jacobs G , Baseer A 
Published: September 2020

Abstract
Considering building a wind farm, a quarter of the initial investment cost is accounted for planning, construction, and project preparation. Some of those expenses can be reduced within the project concept phase. The wind farm layout is one of the common aspects being optimized.
Commonly, wind turbines are placed such that wake losses are minimal. However, this might lead to long access roads. The cost of a gravel road is estimated to be 75 €/m. In this paper, an optimization problem considering access roads is developed.
Two methods are investigated to determine the influence of the access roads on a wind farm layout optimization. A case study with seven wind turbines is set up. The layout is optimized such that the LCOE is minimal. One method examines a wind farm with nearby existing roads. This method results in a reduction of road costs by 9 000€ while the AEP suffers a loss of 0.134 %. The second method neglects existing roads and develops a new access road network. Comparing an optimized wind farm layout without considering the access roads to an optimization that included the access leads to 22 000 € fewer road investment costs and a loss of AEP of 0.238 %. Those changes seem marginal but indicate a possible gain for large scale wind farms.
Lidar-assisted control in wind turbine design: Where are the potential benefits?
Authors: Canet H , Löw S , Bottasso CL 
Published: September 2020

Abstract
This study explores the potential benefits of considering Lidar-assisted control (LAC) at the first stages of wind turbine design. The proposed methodology starts with a load analysis of several reference wind turbines to understand which design constraints can be influenced by the use of LAC. The blade and tower of each analyzed model are redesigned considering LAC-induced reductions in key driving quantities. Preliminary results suggest modest reductions in LCOE with potentially significant benefits limited to the tower. The study also discusses the requirements on LAC system purchase and O&M costs, for both onshore and offshore machines, to achieve a reduction in LCOE.
Efficient structural optimisation of a 20 MW wind turbine blade
Authors: Scott S , Greaves P , Weaver P M , Pirrera A , Macquart T 
Published: September 2020

Abstract
This paper presents, through the structural design of a 20 MW wind turbine blade, a selection of novel analysis and optimisation methods for wind turbines. These methods are integrated in the software—Aeroelastic Turbine Optimisation Methods (ATOM). A key feature is the novel, computationally-efficient piecewise linear model for running rapid design load case simulations (up to 16 times speed-up over conventional methods). Further, a comprehensive set of realistic design constraints is also proposed to ensure structural feasibility and aeroelastic stability. To demonstrate these methods, a sequential gradient-based optimisation process is employed, relying on the globally convergent method of moving asymptotes (GCMMA). The process begins with an aerodynamic optimisation to generate twist distributions, followed by an iterative loop during which load envelope updates and ‘frozen-load’ blade structural optimisations are performed independently. Aeroelastic loads are therefore considered, but are not directly optimised for. The present study investigates the structural design of a 20 MW wind turbine blade with hybrid carbon-glass spar caps. The optimised 122 m blade is found to have a mass of 83,622 kg, which decreases to 81,396 kg (-2.66%) with the addition of sweep. The GCMMA is found to converge successfully at each structural optimisation step. By contrast, the iterative loop is observed to oscillate, albeit within small bounds. Finally, results suggest that convergence of multi-step optimisation methods for aeroelastic blade design may not be guaranteed if design variables inducing aeroelastic couplings are considered.
Integration of System Level CFD Simulations into the Development Process of Wind Turbine Prototypes
Authors: Arnold Matthias , Wenz Florian , Kühn Timo , Lutz Thorsten , Altmikus Andree 
Published: September 2020

Abstract
During the development process of wind turbines, there is a rising demand for detailed flow and multi-physics analyses. Especially the system level computational fluid dynamics (CFD), focusing not on a single component or aspect, but on the turbine as a system of geometric and dynamic properties can be used to improve the turbine quality and time to market. In this paper the integration of the system level CFD into the development process of Enercon wind turbines is introduced. Further two example applications are detailed presenting the benefits of CFD based nacelle anemometer calibration and a risk assessment study based on aero-servo-elastic CFD simulations.
Study on influence of blade icing on operational characteristics of wind turbine at cold climate
Authors: Goshima N , Maeda T , Kamada Y , Tada T , Hanamura M , Pham H H , Iwai K , Fujiwara A , Hosomi M 
Published: September 2020

Abstract
In this paper, the icing effect on wind turbine is investigated. The sectional aerodynamic performance of iced blade was measured in wind tunnel with icing airfoil models. The analysis conducted by using FAST using the measured sectional performance was conducted to investigate the degradation in wind turbine performance and added load due to icing. Frequency analysis was also conducted with the time series data calculated by using FAST. As the results, the power output at the rated wind speed for the icing case is smaller than that for the clean case and the maximum rotor thrust for the icing case is smaller than the clean case. The wind speed at which the turbine’s rated power is reached for the icing case was higher than that for the clean case.
Optimization of the erosion-safe operation of the IEA Wind 15 MW Reference Wind Turbine
Authors: Skrzypiński W R , Bech J I , Hasager Ch B , Tilg A-M , Ch Bak F Vejen 
Published: September 2020

Abstract
The work describes modelling of erosion of the IEA 15 MW Reference Wind Turbine. Five-year worth of historical time series including wind speed, rain intensity and price of energy was used in the modelling. The work included erosion-safe operation of the turbine where the tip speed was limited during rain events to prevent erosion. The tip-speed limit was defined as a function of rain intensity and price of energy, the distribution of which was subject to an optimization. The objective for the optimization was to maximize the profit. The factors taken into account in the modelling and optimization were: the loss in power curve due to erosion, and the cost of repair and associated downtime. The results indicated that for this particular turbine it would be sufficient to define the tip-speed limit as a function of rain intensity alone. The model showed that 88% of the overall profit loss due to erosion could be saved by running the turbine in the erosion-safe operation. Although some inaccuracy may be associated with the modelling, the results strongly indicate that a significant amount of money could be saved by utilizing the erosion-safe operation on offshore turbines.
The influence of the bound vortex on the aerodynamics of curved wind turbine blades
Authors: Li Ang , Gaunaa Mac , Pirrung Georg Raimund , Ramos-García Néstor , González Horcas Sergio 
Published: September 2020

Abstract
Passive load alleviation on wind turbine blades can be achieved through geometric bend-twist coupling, for example by sweeping the blade backwards. In order to obtain the correct load distribution of a curved blade with in-plane sweep and/or out-of-plane dihedral, the influence of the blade shape on the aerodynamics must be modelled correctly. This includes the influence of the curved bound vortex, and it is especially important when designing a wind turbine blade with aeroelastic tailoring. In this paper, the background for modelling the curved bound vortex influence will be described in detail and a modified method is proposed. The proposed method of bound vorticity modelling is compared for curved and straight translating wings as well as wind turbine blades with results from a panel code and a Navier-Stokes solver. From this comparison, the advantages of the current modification with respect to the other lifting-line implementations are shown. The method proposed in the present work is general and applicable to any lifting-line like model.
Validation of analytical body force model for actuator disc computations
Authors: Sørensen Jens N , Andersen Søren J 
Published: September 2020

Abstract
A new analytical model for representing body forces in numerical actuator disc models of wind turbines is compared to results from a BEM model. The model assumes the rotor disc being subject to a constant circulation, modified for tip and root effects. The advantage of the model is that it does not depend on any detailed knowledge concerning the actual wind turbine being analysed, but only requires information of the thrust coefficient and tip speed ratio. The model is validated for different turbines operating under a wide range of operating conditions. The comparisons show generally an excellent agreement with the BEM model, with, however, some deviations of the tangential force in the root area and at small values of the thrust coefficient.
On the importance of the beam reference line
Authors: Couturier P J , Mailly L , Molitor D , Wang Q 
Published: September 2020

Abstract
The development of a new beam reference line to improve bend-twist response modelling is presented. The beam reference line is derived as the locus of the cross-section elastic energy centres under pure bending moment. The performance of the new reference line is assessed via experimental measurements performed on a Siemens Gamesa wind turbine blade. Bend-twist modelling capability is assessed by comparing the location of the zero-twist rotation line and zero-twist-rate lines.
Comparison of a radially resolved dynamic inflow pitch step experiment to mid-fidelity simulations and BEM
Authors: Berger Frederik , Höning Leo , Herráez Iván , Kühn Martin 
Published: September 2020

Abstract
In this paper a detailed comparison of the experimental and numerical results of a scaled wind turbine model in a wind tunnel subjected to fast pitching steps leading to the so-called dynamic inflow effect is presented. We compare results of an Actuator Line LES tool, a vortex code and four engineering models, to the experiment. We perform one and two time constant model analysis of axial wake induction and investigate the overshooting of integral loads. Our results show, that the effect is captured better by the two time constant models than by the one time constant models. Also the experiment and mid-fidelity simulations are best described by a two time constant fit. We identify the best dynamic inflow model to be the 0ye model. Different possibilities for the improvement of dynamic inflow models are discussed.
Investigation of the individual load distribution of a blade bearing test rig by means of finite element simulation
Authors: Leupold S. , Schelenz R. , Jacobs G. 
Published: September 2020

Abstract
To carry out fatigue tests on the blade bearing test rig used in this work, knowledge of the maximum contact pressure and position of the contact ellipse in each rolling contact is necessary. Since these cannot be measured directly, a detailed FE-model of the blade bearings and the test rig components is set up. Previous studies use non-linear spring to simplify the raceway ball interaction. In this paper each rolling contact is modelled with a surface to surface interaction. This allows the evaluation of the maximum contact pressure and the distance between the contact area and the edge of the raceway. Furthermore, measurements of the relative displacement between the outer and inner ring for different load steps were carried out and show a good correlation with the simulation results.
Wind tunnel tests for vortex generators mitigating leading-edge roughness on a 30% thick airfoil
Authors: Gutiérrez R , Llórente E , Echeverría F , Ragni D 
Published: September 2020

Abstract
In this study, the aerodynamic performance of a thick airfoil is analysed, after installing leading-edge roughness to emulate a severe state on the airfoil surface. The impact on aerodynamic coefficients has been quantified using two roughness methods: zig-zag tape and sandpaper. Wind tunnel tests are carried out at a Reynolds number of 3•106. At low angles of attack, zig-zag tape and sandpaper provide comparable lift and drag coefficients but significant variations of these coefficients are obtained for high angles of attack. Stalled flow is the cause of the most significant variation on the airfoil performance between smooth and rough surface states. Vortex generators are adapted to recover the lift coefficient value previously given by the airfoil under smooth conditions. As a result, vortex generators are able to reduce the loss of lift and the sensitivity of the airfoil to the rough state.
Exploiting the limit of BEM solvers in moonpool type floaters
Authors: Ntouras Dimitris , Manolas Dimitris , Papadakis George , Riziotis Vasilis 
Published: September 2020

Abstract
Solvers based on Boundary Element Method (BEM) are fast and they have proven to provide accurate results in a wide range of applications. On the other hand, computational fluid dynamics (CFD) solvers are high-fidelity tools able to account for viscous effects. However, they are computationally demanding. In the present work, the limitations of BEM solvers are exploited considering the case study of a moonpool type floater in which the viscous effects near the sharp edges of the body (vortex shedding) are not negligible. The BEM results are compared with the results from an unsteady Reynolds averaged Navier-Stokes (URANS) CFD solver and experimental data, while viscous corrections of the BEM method are assessed.
Plasma Actuation for Mitigation of Fluctuating Loads on Airfoils: An Experimental Study
Authors: Rezaeiha Abdolrahim , Kotsonis Marios 
Published: September 2020

Abstract
Wind tunnel measurements are performed to investigate the potential for mitigation of aerodynamic load fluctuations on airfoils, as the main source of fatigue for wind turbines, using plasma actuators. The experiment consists of aerodynamic force measurements using six strain gauges and 2-component velocity measurements using particle image velocimetry (PIV). The analysis is focused on the aerodynamic loads, the mean flow, the turbulent kinetic energy and the proper orthogonal decomposition (POD) modes and their energy budget. The main findings are: (i) the actuation increased the lift coefficient for all the range of a, with an average and maximum increment of 0.05 and 0.1, per unit span of the actuator; (ii) the actuation deflects the airfoil near wake downward, resulting in the so-called virtual cambering effect; (iii) the actuation increases the TKE near the trailing edge, which could increase the airfoil trailing-edge noise; (iv) the POD analysis reveals that the actuation increases the size of the vortical structures in the near wake and the energy budget of the first POD modes, esp. at high angles of attack prior to stall.
Effect of wind directionality on fatigue life of monopile support structures for offshore wind turbines
Authors: Nozari A , Kuchma D , Hines E M 
Published: September 2020

Abstract
The U.S. offshore wind industry can expect higher costs due to the lack of domestic experience with offshore wind technology. A key factor of the capital expenditure related to offshore wind farms is the cost of the support structures of offshore wind turbines. Therefore, improvements to the reliability of support structures under ultimate and fatigue loading conditions will help reduce the levelized cost of energy of offshore wind. This study presents a framework that accounts for the wind directionality by assuming a distinct and independent wind speed distribution per each wind direction and investigates its effect on the fatigue life of offshore wind turbine support structures. A monopile support structure in a potential wind site close to a National Oceanic and Atmospheric Administration buoy in the north-eastern US waters is used in this study. Fatigue damage assessment is performed for the normal operational condition of wind turbine, and the results are presented considering both cathodic protection and free corrosion conditions at the mudline level of the monopile. The location and extent of the predicted fatigue damages are found to vary due to accounting for the wind directionality.
Effect of varying fidelity turbine models on wake loss prediction
Authors: Liew Jaime , Raimund Pirrung Georg , Meseguer Urbán Albert 
Published: September 2020

AbstractWind farm simulations are widely used in estimating energy yield and for optimal wind farm layout design. In the early design stages of a wind farm, low fidelity wind turbine models are used to estimate the farm power output, often due to incomplete knowledge of the turbine characteristics and the additional complexities. The discrepancies introduced in a wind farm simulation as a result of using low fidelity models can often be overlooked, leading to a misrepresentation of a wind farm’s yield. In this paper, the discrepancies between five levels of fidelity for two turbine designs are quantified, focusing on the produced wake and the downstream flow effects. Two high fidelity aeroelastic turbine models and three low fidelity models are described, where the wake is produced using the Dynamic Wake Meandering (DWM) model for each turbine and model. The results provide insight into the expected uncertainties in wake simulations as a result of changing the turbine fidelity level.
Cross-correlation-based approach to align turbulent inflow between CFD and lower-fidelity-codes in wind turbine simulations
Authors: Wenz F , Boorsma K , Lutz T , Krämer E 
Published: September 2020

Abstract
In cases with turbulent inflow, the analysis of the temporal development of forces could provide more insight into differences in calculated fatigue loads of wind turbines. While lifting-line-codes and the Blade-Element-Momentum (BEM) approach do not resolve the inflow, Computational Fluid-Dynamic (CFD) codes resolve the entire flow field. A comparison of time series between the different codes therefore requires a consistent input of the background turbulence. This was enabled by extracting the turbulent velocity field from empty box (without rotor) CFD simulations at the anticipated rotor position. The presence of a rotor in the CFD simulations leads to a delay in the inflow due to the induced velocity. This blockage effect of the rotor was quantified by a cross-correlation. The velocity field extracted from the simulation of the empty box was shifted by the resulting temporal offset before it was used as lifting-line-code or BEM input. Thus, a time-dependent load comparison between the codes could be performed. It was found that the difference in load predictions between CFD and BEM seems to be larger at peak values. For cases with high thrust coefficient or high turbulence intensity, a simpler analytical approach resulted in significantly higher temporal offsets than the cross-correlation.
Synthetic wind speed generation for the simulation of realistic diurnal cycles
Authors: Ambrosio D D , Schoukens J , Troyer T De , Zivanovic M , Runacres M C 
Published: September 2020

Abstract
Synthetic wind-speed generators can provide a detailed characterisation of the wind variability at different time scales. A keen interest in the availability of synthetic wind speeds has recently risen in wind power modelling applications. In particular, a proper simulation of the diurnal and annual variability of the wind speed is sought that can lead to a more efficient grid integration of this renewable source. This paper proposes a statistical model for generating synthetic wind speeds consistent with both the probability density function and the spectral density function of a measured wind-speed dataset and that simulates accurately its average diurnal variation. To test the proposed methodology, multiple synthetic time series are generated using three long-term wind-speed time series recorded at a meteorological site in the Netherlands. The accuracy in terms of the statistical descriptors of the generated time series and their average diurnal variation is assessed with respect to the target data. We show that the average diurnal cycles present in all the three measured time series are always reproduced accurately, and that the statistical descriptors of the target dataset are constantly matched with high accuracy. Possible advantages of the present approach in terms of power system modelling are discussed.
Development of a streamline wake model for wind farm performance predictions
Authors: Sessarego Matias , Feng Ju , Friis-Møller Mikkel , Xu Yun , Xu Mengying , Zhong Shen Wen 
Published: September 2020

Abstract
In the present paper a new streamline model for wake development based on a streamline topology is applied and compared with different approaches for modeling the wind turbine wakes. The contribution of the present work is the comparison of the streamline-and straight-wake models as well as the different wake models, e.g., Jensen and Gaussian. The models have been applied to two wind farm cases. The results from the first case are compared against SCADA measurements and computational fluid dynamics simulations (CFD). The CFD simulations are performed using Reynolds-Averaged Navier Stokes (RANS) together with the actuator disc (AD) approach. The mean percent difference in power using the different wake models ranged between 19-20%. Mean percent difference in power for the AD-RANS was approximately 20%. For the second wind farm case only wake models are compared and approximately ±1% difference exists between them. The present work shows that the streamline topology of the wind turbine wake flow as well as the wake models have an effect on the performance prediction of wind farms.