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  • 1.
    Ahlström, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Emergency stop simulation using a finite element model developed for large blade deflections2006In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 9, no 3, p. 193-210Article in journal (Refereed)
    Abstract [en]

    Predicting the load in every possible situation is necessary in order to build safe and optimized structures. A highly dynamical case where large loads are developed is an emergency stop. Design simulation tools that can cope with the upcoming non-linearities will be especially important as the turbines get bigger and more flexible. The model developed here uses the advanced commercial finite element system MSC.Marc, focused on non-linear design and analysis, to predict the structural response. The aerodynamic model named AERFORCE, used to transform the wind to loads on the blades, is a blade element momentum model. A comparison is made between measured and calculated loads for the Tjaere-borg wind turbine during emergency braking of the rotor. The simulation results correspond well with measured data. The conclusion is that the aeroelastic tool is likely to perform well when simulating more flexible turbines.

  • 2.
    Ahlström, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Influence of wind turbine flexibility on loads and power production2006In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 9, no 3, p. 237-249Article in journal (Refereed)
    Abstract [en]

    Most aeroelastic codes used today assume small blade deflections and application of loads on the undeflected structure. However, with the design of lighter and more flexible wind turbines, this assumption is not obvious. By scaling the system mass and stiffness properties equally, it is possible to compare wind turbines of different degrees of slenderness and at the same time keep system frequencies the some in an undeformed state. The developed model uses the commercial finite element system MSC. Marc, focused on non-linear design and analysis, to predict the structural response. The aerodynamic model AERFORCE, used to transform the wind to loads on the blades, is a blade element momentum model. A comparison is made between different slenderness ratios in three wind conditions below rated wind speed. The results show that large blade deflections have a major influence on power production and the resulting structural loads and must be considered in the design of very slender turbines.

  • 3. Chougule, A.
    et al.
    Mann, J.
    Segalini, Antonio
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Dellwik, E.
    Spectral tensor parameters for wind turbine load modeling from forested and agricultural landscapes2015In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 18, no 3, p. 469-481Article in journal (Refereed)
    Abstract [en]

    A velocity spectral tensor model was evaluated from the single-point measurements of wind speed. The model contains three parameters representing the dissipation rate of specific turbulent kinetic energy, a turbulence length scale and the turbulence anisotropy. Sonic anemometer measurements taken over a forested and an agricultural landscape were used to calculate the model parameters for neutral, slightly stable and slightly unstable atmospheric conditions for a selected wind speed interval. The dissipation rate above the forest was nine times that at the agricultural site. No significant differences were observed in the turbulence length scales between the forested and agricultural areas. Only a small difference was observed in the turbulence anisotropy at the two sites, except near the surface, where the forest turbulence was more isotropic. The turbulence anisotropy remained more or less constant with height at the forest site, whereas the turbulence became more isotropic with height for the agricultural site. Using the three parameters as inputs, we quantified the performance of the model in coherence predictions for vertical separations. The model coherence of all the three velocity components was overestimated for the analyzed stability classes at both sites. As expected from the model approximations, the model performed better at both sites for neutral stability than slightly stable and unstable conditions. The model prediction of coherence of the along-wind and vertical components was better than that of the cross-wind component. No significant difference was found between the performance of the model at the forested and the agricultural areas.

  • 4. Ebenhoch, Raphael
    et al.
    Muro, Blas
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Dahlberg, Jan-Åke
    Berkesten Hägglund, Patrik
    Segalini, Antonio
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A linearized numerical model of wind-farm flows2017In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 20, no 5, p. 859-875Article in journal (Refereed)
    Abstract [en]

    A fast and reasonably accurate numerical three-dimensional wake model able to predict the flow behaviour of a wind farm over a flat terrain has been developed. The model is based on the boundary-layer approximation of the Navier-Stokes equations, linearized around the incoming atmospheric boundary layer, with the assumption that the wind turbines provide a small perturbation to the velocity field. The linearization of the actuator-disc theory brought additional insights that could be used to understand the behaviour, as well as the limitations, of a flow model based on linear methods: for instance, it is shown that an adjustment of the turbine's thrust coefficient is necessary in order to obtain the same wake velocity field provided by the actuator disc theory within the used linear framework. The model is here validated against two independent wind-tunnel campaigns with a small and a large wind farm aimed at the characterization of the flow above and upstream of the farms, respectively. The developed model is, in contrary to current engineering wake models, able to account for effects occurring in the upstream flow region, thereby including more physical mechanisms than other simplified approaches. The conducted simulations (in agreement with the measurement results) show that the presence of a wind farm affects the approaching flow far more upstream than generally expected and definitely beyond the current industrial standards. Despite the model assumptions, several velocity statistics above wind farms have been properly estimated providing an insight into the transfer of momentum inside the turbine rows.

  • 5. Holttinen, Hannele
    et al.
    Meibom, Peter
    Orths, Antje
    Lange, Bernhard
    O'Malley, Mark
    Tande, John Olav
    Estanqueiro, Ana
    Gomez, Emilio
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Strbac, Goran
    Smith, J. Charles
    van Hulle, Frans
    Impacts of large amounts of wind power on design and operation of power systems, results of IEA collaboration2011In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 14, no 2, p. 179-192Article in journal (Refereed)
    Abstract [en]

    There are dozens of studies made and ongoing related to wind integration. However, the results are not easy to compare. IEA WIND R&D Task 25 on 'Design and Operation of Power Systems with Large Amounts of Wind Power' collects and shares information on wind generation impacts on power systems, with analyses and guidelines on methodologies. In the state-of-the-art report (October, 2007), and the final report of the 3 years period (July, 2009) the most relevant wind power grid integration studies have been analysed especially regarding methodologies and input data. Several issues that impact on the amount of wind power that can be integrated have been identified. Large balancing areas and aggregation benefits of wide areas help in reducing the variability and forecast errors of wind power as well as help in pooling more cost effective balancing resources. System operation and functioning electricity markets at less than day-ahead time scales help reduce forecast errors of wind power. Transmission is the key to aggregation benefits, electricity markets and larger balancing areas. Best practices in wind integration studies are described. There is also benefit when adding wind power to power systems: it reduces the total operating costs and emissions as wind replaces fossil fuels and this should be highlighted more in future studies.

  • 6.
    Hyvärinen, Ann
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lacagnina, Giovanni
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. University of Southampton, Faculty of Engineering and the Environment.
    Segalini, Antonio
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A wind-tunnel study of the wake development behind wind turbines over sinusoidal hills2018In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 21, no 8, p. 605-617Article in journal (Refereed)
    Abstract [en]

    In the present work, the wake development behind small-scale wind turbines is studied when introducing local topography variations consisting of a series of sinusoidal hills. Additionally, wind-tunnel tests with homogeneous and sheared turbulent inflows were performed to understand how shear and ambient turbulence influence the results. The scale of the wind-turbine models was about 1000times smaller than full-size turbines, suggesting that the present results should only be qualitatively extrapolated to real-field scenarios. Wind-tunnel measurements were made by means of stereoscopic particle image velocimetry to characterize the flow velocity in planes perpendicular to the flow direction. Over flat terrain, the wind-turbine wake was seen to slowly approach the ground while it propagated downstream. When introducing hilly terrain, the downward wake deflection was enhanced in response to flow variations induced by the hills, and the turbulent kinetic energy content in the wake increased because of the speed-up seen over the hills. The combined wake observed behind 2 streamwise aligned turbines was more diffused and when introducing hills, it was more prone to deflect towards the ground compared to the wake behind an isolated turbine. Since wake interactions are common at sites with multiple turbines, this suggested that it is important to consider the local hill-induced velocity variations when onshore wind farms are analysed. Differences in the flow fields were seen when introducing either homogeneous or sheared turbulent inflow conditions, emphasizing the importance of accounting for the prevailing turbulence conditions at a given wind-farm site to accurately capture the downstream wake development.

  • 7.
    Ivanell, Stefan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mikkelsen, Robert
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Henningson, Dan
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Actuator disc modelling of wake interaction in Horns Rev wind farmIn: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824Article in journal (Other academic)
    Abstract [en]

    Large eddy simulations of the Navier-Stokes equations are performed tosimulate the Horns Rev off shore wind farm 15 km outside the Danish westcoast. The aim is to achieve a better understanding of the wake interactioninside the farm. The simulations are performed by combining the in-housedeveloped computer code EllipSys3D with the actuator-disc methodology. Inthe actuator-disc method the blades are represented by a disc at which bodyforces representing the aerodynamic loading are introduced. The body forcesare determined by computing local angles of attack and tabulated aerofoil coefficients.The advantage of using the actuator-disc technique is that it is notnecessary to resolve blade boundary layers since the computational resourcesare devoted to simulating the dynamics of the flow structures.In the present study approximately 13.6 million mesh points are used toresolve the wake structure in the park. The park contains 80 wind turbinesdistributed over an area of about 20km2. Since it is not possible to simulate allturbines, the 2 central columns of turbines have been simulated with periodicboundary conditions. This corresponds to an infinitely wide farm with 10turbines in downstream direction. Simulations were performed within plusminus 15 degrees of the turbine alignment, making the wide farm approximationreasonable.The results from the CFD simulations are evaluated and the downstreamevolution of the velocity field is depicted. Special interest is given to whatextent the production is dependent on the inflow angle and turbulence level.The study shows that the applied method captures the main productionvariation within the wind farm. The result further demonstrates that levelsof production correlate well with measurements. However, in some cases thevariation of the measurement data is caused by variation of measurement conditionswith inflow angles.

  • 8.
    Ivanell, Stefan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mikkelsen, Robert
    Henningson, Dan
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Analysis of numerically generated wake structures2009In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 1, p. 63-80Article in journal (Refereed)
    Abstract [en]

    Direct numerical simulations of the Navier-Stokes equations are performed to achieve a better understanding of the behaviour of wakes generated by wind turbines. The simulations are performed by combining the in-house developed computer code EllipSys3D with the actuator-line methodology. In the actuator-line method, the blades are represented by lines along which body forces representing the loading are introduced. The body forces are determined by computing local angles of attack and using tabulated aerofoil coefficients. The advantage of using the actuator-line technique is that it is not needed to resolve blade boundary layers and instead the computational resources are devoted to simulating the dynamics of the flow structures. In the present study, approximately 5 million mesh points are used to resolve the wake structure in a 120-degree domain behind the turbine. The results from the computational fluid dynamics (CFD) simulations are evaluated and the downstream evolution of the velocity field is depicted. Special interest is given to the structure and position of the tip vortices. Further, the circulation from the wake flow field is computed and compared to the distribution of circulation on the blades.

  • 9.
    Ivanell, Stefan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mikkelsen, Robert
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Henningson, Dan
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Stability analysis of the tip vortices of a wind turbine2010In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 13, no 8, p. 705-715Article in journal (Refereed)
    Abstract [en]

     

    The aim of the present project is to obtain a better understanding of thestability properties of wakes generated by wind turbine rotors. To accomplishthis a numerical study on the stability of the tip vortices of the Tjaereborgwind turbine has been carried out. The numerical model is based on large eddysimulations of the Navier-Stokes equations using the actuator line method togenerate the wake and the tip vortices. To determine critical frequencies theflow is disturbed by inserting harmonic perturbations.The results show that the instability is dispersive and that growth arisesonly for some specific frequencies and type of modes. The study also providesevidence of a relationship between the turbulence intensity and the length ofthe near wake. The relationship however needs to be calibrated against measurements.

  • 10. Jauch, C.
    et al.
    Matevosyan, Julija
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ackermann, T.
    Bolik, S.
    International Comparison of Requirements for Connection of Wind Turbines to Power Systems2005In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 8, no 3, p. 295-306Article in journal (Refereed)
    Abstract [en]

    Power production from wind turbines has increased considerably during the lost decade. Therefore today's wind turbines, which are typically set up in wind farms, have a significant influence on the operation of power systems. The efficient and secure operation of power systems is supported by grid codes, which are sets of requirements for all network users (suppliers, customers, etc.). In Europe, several transmission network operators have introduced special grid connection requirements for wind farms. These requirements are mainly based on existing grid codes, initially written for conventional power plants usually equipped with synchronous generators. This article presents a comparison of grid connection requirements for wind farms issued, or proposed as a draft, by transmission network operators in Denmark, Sweden, Germany, Scotland and Ireland.

  • 11.
    Kiviluoma, Juha
    et al.
    Smart Energy and System Integration.
    Holttinen, Hannele
    Smart Energy and System Integration.
    David Edward, Weir
    Scharff, Richard
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Menemenlis, Nickie
    Institut de recherche d'Hydro-Québec.
    Nicolaos, Cutululis
    Department of Wind Energy.
    Danti Lopez, Irene
    University College Dublin, Electricity Research Centre.
    Lannoye, Eamonn
    Electric Power Research Institute.
    Estanqueiro, Ana
    Universidad de Castilla-La-Mancha, Intituto de Investigación en Energías Renovables.
    Zhang, Qin
    State Grid Corporation of China.
    Bai, Jianhua
    State Grid Energy Research Institute.
    Wan, Yih-Huei
    National Renewable Energy Laboratory,Transmission and Grid Integration Group.
    Michael, Milligan
    National Renewable Energy Laboratory, Transmission and Grid Integration Group.
    Variability in Large-Scale Wind Power Generation2016In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 19, no 9, p. 1649-1665Article in journal (Refereed)
    Abstract [en]

    The article demonstrates the characteristics of wind power variability and net load variability in multiple power systems based on real data from multiple years. Demonstrated characteristics include probability distribution for different ramp durations, seasonal and diurnal variability, and low net load events. In some characteristics the power systems are different, but in others they are significantly similar. Somewhat surprisingly there seems to be no straightforward correlation between wind power penetration level and variability. As long as there are several wind power plants with enough geographical spread, most of the smoothing impact is captured. Wind power variability is mainly explained by the extent of geographical spread, but also higher capacity factor causes higher variability. It was also shown how wind power ramps are auto correlated and dependent on the operating output level. In most cases wind power did not have strong diurnal or seasonal variations in the variability. However, there can be exceptions depending on the latitude and on the local characteristics of the wind resource.

  • 12.
    Lindgren, Elin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Minimizing regulation costs in multi-area systems with uncertain wind power forecasts2008In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 11, no 1, p. 97-108Article in journal (Refereed)
    Abstract [en]

    In a power system where there are many fast and/or large changes in generation or consumption, e.g. in a system with large amounts of wind power, it is more complicated to handle the frequency control efficiently. Minimizing regulation costs for the system operator in such a system requires the possibility to simulate the frequency control in the time range from minutes to a few hours. In this paper, it is shown how the frequency control during normal operation can be optimized using a multi-area model, without exceeding frequency limits or transmission capacity. The model has also been expanded to include uncertainties in wind power forecasts, which may lead to an increase of the regulating costs. The optimization model is applied to numerical examples to show the impact of wind power on costs for regulating power and to show the value of better wind speed forecasts. No load forecast errors are taken into account.

  • 13.
    Matevosyan, Julija
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Short Term Hydro Power Planning Coordinated with Wind Power in Areas with Congestion Problems2007In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 10, no 3, p. 195-208Article in journal (Refereed)
    Abstract [en]

    In this paper, a day-ahead planning algorithm for a multi-reservoir hydropower system coordinated with wind power is developed Coordination applies to real situations, where wind power and hydropower are owned by different utilities, sharing the same transmission lines, although hydropower has priority for transmission capacity. Coordination is thus necessary to minimize wind energy curtailments during congestion situations. The planning algorithm accounts for the uncertainty of wind power forecast. Only planning for the spot market is considered. Once the production bid is placed on the market, it cannot be changed. The solution of the stochastic optimization problem should, therefore, fulfill the transmission constraints for all wind power production scenarios. An evaluation algorithm is also developed to quantify the impact from the coordinated planning in the long run. The developed planning algorithm and the evaluation algorithm are applied in a case study. The results are compared with uncoordinated operation. The results of the case study show that coordination with wind power brings additional income to the hydropower utility and leads to significant reduction of wind energy curtailments.

  • 14. Medici, D.
    et al.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Measurements behind model wind turbines: Further evidence of wake meandering2008In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 11, no 2, p. 211-217Article in journal (Refereed)
    Abstract [en]

    The frequency of wind turbine wake meandering was studied using wind turbine models with one, two and three blades. The one-bladed turbine did not give rise to any meandering motion, whereas meandering was observed for both the two- and three-bladed turbines at high enough rotational speeds. It was shown that both the thrust of the turbine and the tip-speed ratio influence the meandering.

  • 15. Medici, D.
    et al.
    Ivanell, S.
    Dahlberg, J-Å
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    The upstream flow of a wind turbine: blockage effect2011In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 14, no 5, p. 691-697Article in journal (Refereed)
    Abstract [en]

    The flow upstream a wind turbine is studied in order to investigate blockage effects. We use rotating wind turbine models in a wind tunnel, where velocity measurements have been made both with hot-wire anemometry up to approximately 4.5 diameters (D) upstream the turbine, as well as laser particle image velocimetry measurements close to the turbine rotor. Also, numerical simulations have been carried out by means of a finite volume code. The measurements show, among other things, that the flow is affected more than 3 D upstream the rotor plane.

  • 16.
    Medici, Davide
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Alfredsson, Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Measurements on a wind turbine wake: 3D effects and bluff-body vortex shedding2006In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 9, no 3, p. 219-236Article in journal (Refereed)
    Abstract [en]

    The velocity held in the wake of a two-bladed wind turbine model (diameter 180 mm) has been studied under different conditions using a two-component hot wire. All three velocity components were measured both for the turbine rotor normal to the oncoming flow as well as with the turbine inclined to the freestream direction (the yaw angle was varied from 0 degrees to 20 degrees). The measurements showed, as expected, a wake rotation in the opposite direction to that of the turbine. A yawed turbine is found to clearly deflect the wake flow to the side, showing the potential of controlling the woke by yawing the turbine. An unexpected feature of the flow was that spectra from the time signals showed the appearance of a low-frequency fluctuation both in the wake and in the flow outside the wake. This fluctuation was found both with and without freestream turbulence and also with a yawed turbine. The frequency expressed as a Strouhal number was shown to be independent of the freestream velocity or turbulence level, but the low frequency was only observed when the tip speed ratio (or equivalently the drag coefficient) was high. The shedding frequency changed also with the yaw angle. This is in agreement with the idea that the turbine sheds structures as a bluff body. The phenomenon, noticeable in all the velocity components, was further investigated using two-point cross-correlations of the velocity signals.

  • 17.
    Nilsson, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Uppsala University Campus Gotland, Sweden.
    Ivanell, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Uppsala University Campus Gotland, Sweden.
    Hansen, Kurt S.
    Mikkelsen, Robert
    Sørensen, Jens N.
    Breton, Simon-Philippe
    Henningson, Dan
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Large-eddy simulations of the Lillgrund wind farm2015In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 18, no 3, p. 449-467Article in journal (Refereed)
    Abstract [en]

    The power production of the Lillgrund wind farm is determined numerically using large-eddy simulations and compared with measurements. In order to simulate realistic atmospheric conditions, pre-generated turbulence and wind shear are imposed in the computational domain. The atmospheric conditions are determined from data extracted from a met mast, which was erected prior to the establishment of the farm. In order to allocate most of the computational power to the simulations of the wake flow, the turbines are modeled using an actuator disc method where the discs are imposed in the computational domain as body forces which for every time step are calculated from tabulated airfoil data. A study of the influence of imposed upstream ambient turbulence is performed and shows that higher levels of turbulence results in slightly increased total power production and that it is of great importance to include ambient turbulence in the simulations. By introducing ambient atmospheric turbulence, the simulations compare very well with measurements at the studied inflow angles. A final study aiming at increasing the farm production by curtailing the power output of the front row turbines and thus letting more kinetic energy pass downstream is performed. The results, however, show that manipulating only the front row turbines has no positive effect on the farm production, and therefore, more complex curtailment strategies are needed to be tested.

  • 18. Nilsson, Karl
    et al.
    Shen, W. Z.
    Sørensen, J. N.
    Breton, S. -P
    Ivanell, Stefan
    Erratum: Validation of the actuator line method using near wake measurements of the Mexico rotor (Wind Energy (2015) 18 (499-514))2015In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 18, no 9Article in journal (Refereed)
  • 19.
    Nilsson, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. Uppsala University Campus Gotland, Sweden .
    Shen, Wen Z.
    Sørensen, Jens N.
    Breton, Simon-Philippe
    Ivanell, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics. Uppsala University Campus Gotland, Sweden.
    Validation of the actuator line method using near wake measurements of the MEXICO rotor2015In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 18, no 3, p. 499-514Article in journal (Refereed)
    Abstract [en]

    The purpose of the present work is to validate the capability of the actuator line method to compute vortex structures in the near wake behind the MEXICO experimental wind turbine rotor. In the MEXICO project/MexNext Annex, particle image velocimetry measurements have made it possible to determine the exact position of each tip vortex core in a plane parallel to the flow direction. Determining center positions of the vortex cores makes it possible to determine the trajectory of the tip vortices, and thus the wake expansion in space, for the analyzed tip speed ratios. The corresponding cases, in terms of tip speed ratios, have been simulated by large-eddy simulations using a Navier - Stokes code combined with the actuator line method. The flow field is analyzed in terms of wake expansion, vortex core radius, circulation and axial and radial velocity distributions. Generally, the actuator line method generates significantly larger vortex cores than in the experimental cases, but predicts the expansion, the circulation and the velocity distributions with satisfying results. Additionally, the simulation and experimental data are used to test three different techniques to compute the average axial induction in the wake flow. These techniques are based on the helical pitch of the tip vortex structure, 1D momentum theory and wake expansion combined with mass conservation. The results from the different methods vary quite much, especially at high values of λ.

  • 20.
    Sarmast, Sasan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. Technical University of Denmark, Denmark.
    Segalini, Antonio
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Mikkelsen, Robert F.
    Ivanell, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Comparison of the near-wake between actuator-line simulations and a simplified vortex model of a horizontal-axis wind turbine2016In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 19, no 3, p. 471-481Article in journal (Refereed)
    Abstract [en]

    The flow around an isolated horizontal-axis wind turbine is estimated by means of a new vortex code based on the Biot-Savart law with constant circulation along the blades. The results have been compared with numerical simulations where the wind turbine blades are replaced with actuator lines. Two different wind turbines have been simulated: one with constant circulation along the blades, to replicate the vortex method approximations, and the other with a realistic circulation distribution, to compare the outcomes of the vortex model with real operative wind-turbine conditions (Tjaereborg wind turbine). The vortex model matched the numerical simulation of the turbine with constant blade circulation in terms of the near-wake structure and local forces along the blade. The results from the Tjaereborg turbine case showed some discrepancies between the two approaches, but overall, the agreement is qualitatively good, validating the analytical method for more general conditions. The present results show that a simple vortex code is able to provide an estimation of the flow around the wind turbine similar to the actuator-line approach but with a negligible computational effort.

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