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  • 1. Andersen, S. J.
    et al.
    Witha, B.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Sørensen, Jens Nørkær
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Mikkelsen, R. F.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Quantifying variability of Large Eddy Simulations of very large wind farms2015Ingår i: Wake Conference 2015, 2015, s. 012027-, artikel-id 012027Konferensbidrag (Refereegranskat)
    Abstract [en]

    Large Eddy Simulations are inherently dynamic as the largest scales are resolved and the smallest scales are modeled temporally. This raises challenges for simulations including very large scales such as atmospheric flows, which require very long simulation times. Simple averages fail at capturing these dynamics and potentially yield misleading interpretations concerning the capabilities of different models when tested in blind tests or in benchmarking exercises such as Wakebench, where results from different flow models are compared. This article will present results from very large wind farm simulations using Actuator Disc (AD) and Line (AL) models for two different turbine spacings with turbulent inflow. The results of each numerical flow model include a certain variability, and it will be examined if different models result in comparable probability distributions.

  • 2.
    Andersen, S.J.
    et al.
    Technical University of Denmark.
    Sørensen, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper. Technical University of Denmark.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Mikkelsen, Robert
    Technical University of Denmark.
    Comparison of Engineering Wake Models with CFD Simulations2014Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 524, s. 012161-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The engineering wake models by Jensen [1] and Frandsen et al. [2] are assessed for different scenarios simulated using Large Eddy Simulation and the Actuator Line method implemented in the Navier-Stokes equations. The scenarios include the far wake behind a single wind turbine, a long row of turbines in an atmospheric boundary layer, idealised cases of an infinitely long row of wind turbines and infinite wind farms with three different spacings. Both models include a wake expansion factor, which is calibrated to fit the simulated wake velocities. The analysis highlights physical deficiencies in the ability of the models to universally predict the wake velocities, as the expansion factor can be fitted for a given case, but with not apparent transition between the cases. 1.

  • 3.
    Breton, Simon-Philippe
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Nilsson, K.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Olivares-Espinosa, H.
    Masson, C.
    Dufresne, L.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Study of the influence of imposed turbulence on the asymptotic wake deficit in a very long line of wind turbines2014Ingår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 70, s. 153-163Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of imposed turbulence on the development of the flow along a long row of wind turbines is studied, in search for an asymptotic wake deficit state. Calculations are performed using EllipSys3D, a CFD code that solves the Navier-Stokes equations in their incompressible form using a finite volume approach. In this code, the Large-Eddy Simulation technique is used for modeling turbulence, and the wind turbine rotors are represented as actuator discs whose loading is determined through the use of tabulated airfoil data by applying the blade-element method. Ten turbines are located along a row and separated from each other by seven rotor diameters, which is representative of the distance used in today's offshore wind farms. Turbulence is pre-generated with the Mann model, with imposed turbulence intensity levels of 4.5% and 8.9%. The aim with this study is to investigate features of the flow that depend solely on imposed turbulence and the presence of wind turbine rotors. For this reason, the turbines are isolated from their environment, and no effect from the presence of the atmospheric boundary layer is modeled, i.e., a non-sheared inflow is used. Analysis of the characteristics of the flow as a function of the position along the row of turbines is performed in terms of standard deviation of the velocity components, turbulence kinetic energy, mean velocity, and power spectra of the axial velocity fluctuations. The mean power production along the row of turbines is also used as an indicator. Calculations are performed below rated power, where a generator torque controller implemented in EllipSys3D renders it possible for the turbines to adapt to the flow conditions in which they operate. The results obtained for the standard deviation of the velocity components, turbulence kinetic energy, power and mean velocity as functions of downstream distance show that an asymptotic wake state seems close to be reached, in the conditions tested, near the end of the 10 turbine row. Significant changes towards this state are seen to happen faster when imposing turbulence in the domain. Power spectra of the axial velocity fluctuations are shown to provide interesting information about the turbulence in the flow, but are found not to be useful in determining if an asymptotic wake state is reached.

  • 4.
    Breton, Simon-Philippe
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Olivares-Espinosa, H.
    Masson, C.
    Dufresne, L.
    Comparative CFD study of the effect of the presence of downstream turbines on upstream ones using a rotational speed control system2014Ingår i: Science of Making Torque from Wind 2012, 2014, Vol. 555Konferensbidrag (Refereegranskat)
    Abstract [en]

    The effect of a downstream turbine on the production of a turbine located upstream of the latter is studied in this work. This is done through the use of two CFD simulation codes, namely OpenFOAM and EllipSys3D, which solve the Navier-Stokes equations in their incompressible form using a finite volume approach. In both EllipSys3D and Open Foam, the LES (Large Eddy Simulation) technique is used for modelling turbulence. The wind turbine rotors are modelled as actuator disks whose loading is determined through the use of tabulated airfoil data by applying the blade-element method. A generator torque controller is used in both simulation methods to ensure that the simulated turbines adapt, in terms of rotational velocity, to the inflow conditions they are submited to. Results from both simulation codes, although they differ slightly, show that the downstream turbine affects the upstream one when the spacing between the turbines is small. This is also suggested to be the case looking at measurements performed at the Lillgrund offshore wind farm, whose turbines are located unusually close to each other. However, for distances used in today's typical wind farms, this effect is shown by our calculations not to be significant.

  • 5.
    Breton, Simon-Philippe
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Olivares-Espinosa, Hugo
    École de technologie supérieure, Department of Mechanical Engineering, Montréal, Canada.
    Masson, Christian
    École de technologie supérieure, Department of Mechanical Engineering, Montréal, Canada.
    Dufresne, Louis
    École de technologie supérieure, Department of Mechanical Engineering, Montréal, Canada.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Study Of The Influence Of Atmospheric turbulence On The Asymptotic wake Deficit In A very Long Line Of Wind Turbines2013Ingår i: Proceedings of the 2013 International Conference on Aerodynamics of Offshore Wind Energy Systems and Wakes (ICOWES 2013), Denmark, 2013, s. 420-434Konferensbidrag (Refereegranskat)
    Abstract [en]

    The influence of atmospheric turbulence on the development of the flow along a long row of wind turbines is studied, in search for an asymptotic wake deficit state. Calculations are performed using EllipSys3D, a CFD code that solves the Navier-Stokes equations in their incompressible form using a finite volume approach. In this code, the Large Eddy Simulation technique is used for modelling turbulence, and the wind turbine rotors are represented as actuator disks whose loading is determined through the use of tabulated airfoil data by applying the blade-element method.

    Ten turbines are located along a row and separated from each other by seven rotor diameters, which is representative of the distance used in today’s offshore wind farms. Turbulence is pregenerated with the Mann model, with imposed turbulent levels of 4.5 and 8.9%. The turbines are in this study isolated from their environment, as no effect from the ground is modeled. This makes the proposed study of the asymptotic wake state behavior easier. Analysis of the characteristics of the flow as a function of the position along the row of turbines is performed in terms of turbulence intensity, mean velocity, and power spectra of the velocity fluctuations. Power production along the row of turbines is also used as an indicator.

    Calculations are performed below rated power, where a generator torque controller implemented in EllipSys3D renders it possible for the turbines to adapt to the inlet conditions in which they operate.

    The results obtained for the turbulence intensity, power and mean velocity as a function of downstream distance show that an asymptotic wake state seems close to be reached near the end of the 10 turbine row. They also show a certain dependency on the imposed level of turbulence. Uncertainties obtained in the power spectra of the velocity fluctuations suggest that further investigation is necessary.

  • 6.
    Breton, Simon-Philippe
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Shen, W.Z.
    Technical University of Denmark, Energivej, Building 414, 2800 Kgs. Lyngby, Denmark.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Validation of the actuator disc and actuator line techniques for yawed rotor flows using the New MEXICO experimental data2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Experimental data acquired in the New MEXICO experiment on a yawed 4.5m diameter rotor model turbine are used here to validate the actuator line (AL) and actuator disc (AD) models implemented in the Large Eddy Simulation code EllipSys3D in terms of loadingand velocity field. Even without modelling the geometry of the hub and nacelle, the AL and AD models produce similar results that are generally in good agreement with the experimental data under the various configurations considered. As expected, the AL model does better at capturing the induction effects from the individual blade tip vortices, while the AD model can reproduce the averaged features of the flow. The importance of using high quality airfoil data (including 3D corrections) as well as a fine grid resolution is highlighted by the results obtained. Overall, it is found that both models can satisfactorily predict the 3D velocity field and blade loading of the New MEXICO rotor under yawed inflow.

  • 7.
    Breton, Simon-Philippe
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Sumner, J.
    Dawson Coll, Dept Phys, Montreal, PQ, Canada..
    Sörensen, J. N.
    DTU Wind Energy, Lyngby, Denmark..
    Hansen, K. S.
    DTU Wind Energy, Lyngby, Denmark..
    Sarmast, S.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    A survey of modelling methods for high-fidelity wind farm simulations using large eddy simulation2017Ingår i: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 375, nr 2091, artikel-id 20160097Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Large eddy simulations (LES) of wind farms have the capability to provide valuable and detailed information about the dynamics of wind turbine wakes. For this reason, their use within the wind energy research community is on the rise, spurring the development of new models and methods. This review surveys the most common schemes available to model the rotor, atmospheric conditions and terrain effects within current state-of-the-art LES codes, of which an overview is provided. A summary of the experimental research data available for validation of LES codes within the context of single and multiple wake situations is also supplied. Some typical results for wind turbine and wind farm flows are presented to illustrate best practices for carrying out high-fidelity LES of wind farms under various atmospheric and terrain conditions. This article is part of the themed issue 'Wind energy in complex terrains'.

  • 8.
    Eriksson, Ola
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Baltscheffsky, M.
    WeatherTech Scandinavia AB, Uppsala, Sweden.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Söderberg, S.
    WeatherTech Scandinavia AB, Uppsala, Sweden.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    The Long distance wake behind Horns Rev I studied using large eddy simulations and a wind turbine parameterization in WRF2017Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 854, artikel-id 012012Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the present paper is to obtain a better understanding of long distance wakes generated by wind farms as a first step towards a better understanding of farm to farm interaction. The Horns Rev I (HR) wind farm is considered for this purpose, where comparisons are performed between microscale Large Eddy Simulations (LES) using an Actuator Disc model (ACD), mesoscale simulations in the Weather Research and Forecasting Model (WRF) using a wind turbine parameterization, production data as well as wind measurements in the wind farm wake. The LES is manually set up according to the wind conditions obtained from the mesoscale simulation as a first step towards a meso/microscale coupling.

    The LES using an ACD are performed in the EllipSys3D code. A forced boundary layer (FBL) approach is used to introduce the desired wind shear and the atmospheric turbulence field from the Mann model. The WRF uses a wind turbine parameterization based on momentum sink. To make comparisons with the LESs and the site data possible an idealized setup of WRF is used in this study.

    The case studied here considers a westerly wind direction sector (at hub height) of 270 ± 2.5 degrees and a wind speed of 8 ± 0.5 m/s. For both the simulations and the site data a neutral atmosphere is considered. The simulation results for the relative production as well as the wind speed 2 km and 6 km downstream from the wind farm are compared to site data. Further comparisons between LES and WRF are also performed regarding the wake recovery and expansion.

    The results are also compared to an earlier study of HR using LES as well as an earlier comparison of LES and WRF. Overall the results in this study show a better agreement between LES and WRF as well as better agreement between simulations and site data.

    The procedure of using the profile from WRF as inlet to LES can be seen as a simplified coupling of the models that could be developed further to combine the methods for cases of farm to farm interaction.

  • 9.
    Eriksson, Ola
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper. Environment and Climate Change Canada.
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Impact of Wind Veer and the Coriolis Force for an Idealized Farm to Farm Interaction Case2019Ingår i: Applied Sciences, E-ISSN 2076-3417, Vol. 9, nr 5, artikel-id 922Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of the Coriolis force on the long distance wake behind wind farms is investigated using Large Eddy Simulations (LES) combined with a Forced Boundary Layer (FBL) technique. When using the FBL technique any mean wind shear and turbulent fluctuations can be added with body forces. The wind shear can also include the mean wind veer due to the Coriolis force. The variation of the Coriolis force due to local deviations from the mean profile, e.g., from wakes, is not taken into account in the FBL. This can be corrected for with an extra source term in the equations, hereon defined as the Coriolis correction. For a row of 4 turbines it is shown that the inclusion of the wind veer turns the wake to the right, while including the Coriolis correction turns it to the left. When including both wind veer and Coriolis correction the impact of wind veer dominates. For an idealized farm to farm interaction case, two farms of 4 * 4 turbines with 6 km in between, it can be seen that when including wind veer and the Coriolis correction a approximately 3% increase in the relative production for a full wake direction can be seen and only a slightly smaller increase can be seen when including only wind veer. The results indicate that FBL can be used for studies of long distance wakes without including a Coriolis correction but efforts need to be taken to use a wind shear with a correct mean wind veer.

  • 10.
    Eriksson, Ola
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Byrkjedal, Øyvind
    Kjeller Vindteknikk.
    Lindvall, Johannes
    Kjeller Vindteknikk.
    Simulating wind farms in the Weather Research and Forecast model, resolution sensitivities.2015Konferensbidrag (Övrigt vetenskapligt)
  • 11.
    Eriksson, Ola
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Lindvall, J.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Wake downstream of the Lillgrund wind farm - A Comparison between LES using the actuator disc method and a Wind farm Parametrization in WRF2015Ingår i: WAKE CONFERENCE 2015, 2015, s. 012028-, artikel-id 012028Konferensbidrag (Refereegranskat)
    Abstract [en]

    Simulations of the Lillgrund wind farm (located between Malmo and Copenhagen) are performed using both Large Eddy Simulation (LES) and mesoscale simulations in WRF. The aim is to obtain a better understanding of wakes generated by entire wind farms in order to improve the understanding of farm to farm interactions. The study compares the results from the two used models for the energy production and the wake characteristics downstream of the wind farm. A comparison is also performed with regards to the production data from the Lillgrund wind farm which has been filtered to be comparable to the case used in the simulations. The studied case, based on a prerun in WRF without any wind farm, has an inflow angle of 222 +/- 2.5 deg, a wind speed at hub height of 9.8 m/s and a near neutral atmosphere. A logarithmic wind shear is used in LES and the turbulence intensity is 5.9%. The WRF simulations use a parameterization for wind farms. The wind farm is treated by the model as a sink of the resolved atmospheric momentum. The total energy extraction and the electrical power are respectively proportional to specified thrust and power coefficients. The generated turbulent kinetic energy are the difference between the total and the electrical power. The LES are performed using the EllipSys3D code applying the actuator disc methodology for representing the presence of the rotors. Synthetic atmospheric turbulence is generated with the Mann model. Both the atmospheric turbulence and the wind shear are introduced using body forces. The production was found to be better estimated in LES. WRF show a slightly higher recovery behind the farm. The internal boundary layer is for the compared simulation setups higher in LES while the wake expansion is about the same in both models. The results from the WRF parameterization could potentially be improved by increasing the grid resolution. For farm to farm interaction a combination of the two methods is found to be of interest.

  • 12.
    Eriksson, Ola
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Mikkelsen, R.
    Hansen, K. S.
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Analysis of long distance wakes of Horns Rev I using actuator disc approach2014Ingår i: Science of Making Torque from Wind 2012, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    The wake recovery behind the Horns Rev wind farm is analysed to investigate the applicability of Large Eddy Simulations (LES) in combination with an actuator disc method (ACD) for farm to farm interaction studies. Periodic boundary conditions on the lateral boundaries are used to model the wind farm (as infinitely wide), using only two columns of turbines. The meteorological conditions of the site are taken into account by introducing wind shear and pre-generated synthetic turbulence to the simulation domain using body forces. Simulations are carried out to study the power production and the velocity deficit in the farm wake. The results are compared to the actual power production as well as to wind measurements at 2 km and 6 km behind the wind farm. The simulated power production inside the farm shows an overall good correlation with the real production, but is slightly overpredicted in the most downstream rows. The simulations overpredict the wake recovery, namely the wind velocity, at long distances behind the farm. Further studies are needed before the presented method can be applied for the simulation of long distance wakes. Suggested parameters to be studied are the development of the turbulence downstream in the domain and the impact of the grid resolution.

  • 13.
    Eriksson, Ola
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Analysis of long distance wakes behind a row of turbines – a parameter study2014Ingår i: Science of Making Torque from Wind, 2014, s. 012152-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Large Eddy Simulations (LES) of the long distance wake behind a row of 10 turbines are conducted to predict wake recovery. The Navier-Stokes solver EllipSys3D is used in combination with the actuator disc concept. Neutral atmospheric conditions are assumed in combination with synthetic turbulence using the Mann method. Both the wind shear profile and turbulence are introduced into the flow field using body forces. Previous simulations using the same simulation method to model the Horns Rev wind farm showed a higher wake recovery at long distances compared to measurements. The current study investigates further the sensitivity to parameters such as the grid resolution, Reynolds number, the turbulence characteristics as well as the impact of using different internal turbine spacings. The clearest impact on the recovery behind the farm could be seen from the background turbulence. The impact of the wind shear on the turbulence level in the domain needs further studies. A lower turbulence level gives lower wake recovery as expected. A lower wake recovery can also be seen for a higher grid resolution. The Reynolds number, apart from when using a very low value, has a small impact on the result. The variation of the internal spacing is seen to have a relatively minor impact on the farm wake recovery.

  • 14.
    Eriksson, Ola
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Large-eddy simulations of wind farm production and long distance wakes2015Ingår i: Wake Conference 2015, 2015, s. 012022-, artikel-id 012022Konferensbidrag (Refereegranskat)
    Abstract [en]

    The future development of offshore wind power will include many wind farms built in the same areas. It is known that wind farms produce long distance wakes, which means that we will see more occasions of farm to farm interaction, namely one wind farm operating in the wake of another wind farm. This study investigates how to perform accurate power predictions on large wind farms and how to assess the long distance wakes generated by these farms. The focus of this paper is the production's and wake's sensitivity to the extension of the grid as well as the turbulence when using Large-eddy simulations (LES) with pregenerated Mann turbulence. The aim is to determine an optimal grid which minimizes blockage effects and ensures constant resolution in the entire wake region at the lowest computational cost. The simulations are first performed in the absence of wind turbines in order to assess how the atmospheric turbulence and wind profile are evolving downstream (up to 12,000 m behind the position where the turbulence is imposed). In the second step, 10 turbines are added in the domain (using an actuator disc method) and their production is analyzed alongside the mean velocities in the domain. The blockage effects are tested using grids with different vertical extents. An equidistant region is used in order to ensure high resolution in the wake region. The importance of covering the entire wake structure inside the equidistant region is analyzed by decreasing the size of this region. In this step, the importance of the lateral size of the Mann turbulence box is also analyzed. In the results it can be seen that the flow is acceptably preserved through the empty domain if a larger turbulence box is used. The relative production is increased (due to blockage effects) for the last turbines using a smaller vertical domain, increased for a lower or narrower equidistant region (due to the smearing of the wake in the stretched area) and decreased when using a smaller turbulence box (due to decreased inmixing) The long distance wake behind the row is most impacted by the use of a smaller turbulence box, while the other simulation setups have less influence on these results. In summary, the results show the importance of having relatively large extensions of the domain, large extensions of the equidistant region and especially large extensions of the turbulence box.

  • 15.
    Ivanell, Stefan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Arnqvist, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Avila, Matias
    Barcelona Supercomp Ctr, Barcelona, Spain.
    Cavar, Dalibor
    Tech Univ Denmark, Wind Energy Dept, Lyngby, Denmark.
    Aurelio Chavez-Arroyo, Roberto
    Natl Renewable Energy Ctr CENER, Pamplona, Spain.
    Olivares-Espinosa, Hugo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Peralta, Carlos
    Wobben Res & Dev MS GmbH, Bremen, Germany.
    Adib, Jamal
    Wobben Res & Dev MS GmbH, Bremen, Germany.
    Witha, Bjoern
    ForWind Carl von Ossietzky Univ Oldenburg, Oldenburg, Germany.
    Micro-scale model comparison (benchmark) at the moderately complex forested site Ryningsnäs2018Ingår i: Wind Energy Science, ISSN 2213-3968, E-ISSN 2366-7443, Vol. 3, nr 2, s. 929-946Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article describes a study in which modellers were challenged to compute the wind field at a forested site with moderately complex topography. The task was to model the wind field in stationary conditions with neutral stratification by using the wind velocity measured at 100 m at a metmast as the only reference. Detailed maps of terrain elevation and forest densities were provided as the only inputs, derived from airborne laser scans (ALSs) with a resolution of 10 m x 10 m covering an area of 50 km x 50 km, that closely match the actual forest and elevation of the site. The participants were free to apply their best practices for the simulation to decide the size of the domain, the value of the geostrophic wind, and every other modelling parameter. The comparison of the results with the measurements is shown for the vertical profiles of wind speed, shear, wind direction, and turbulent kinetic energy. The ALS-based data resulted in reasonable agreement of the wind profile and turbulence magnitude. The best performance was found to be that of large-eddy simulations using a very large domain. For the Reynolds-averaged Navier-Stokes type of models, the constants in the turbulence closure were shown to have a great influence on the yielded turbulence level, but were of much less importance for the wind speed profile. Of the variety of closure constants used by the participating modellers, the closure constants from Sogachev and Panferov (2006) proved to agree best with the measurements. Particularly the use of C-mu approximate to 0.03 in the k-epsilon model obtained better agreement with turbulence level measurements. All except two participating models used the full detailed ground and forest information to model the forest, which is considered significant progress compared to previous conventional approaches. Overall, the article gives an overview of how well different types of models are able to capture the flow physics at a moderately complex forested site.

  • 16.
    Ivanell, Stefan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Carlen, Ingemar
    Nilsson, Karl
    Sarmast, Sasan
    Odemark, Ylva
    Andersen, Sören Juhl
    Tenneler, Görkem
    Eriksson, Ola
    Breton, Simon-Philippe
    Åkervik, Espen
    Gravdahl, Arne
    Fransson, Jens
    Mikkelsen, Robert
    Sörensen, Jens
    Henningson, Dan
    Optimization of Large Wind Farms, The Nordic Consortium, Activity report 2009-2012: Elforsk rapport 13:122013Rapport (Övrigt vetenskapligt)
  • 17.
    Ivanell, Stefan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Leweke, T.
    Sarmast, Sasan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Quaranta, H. U.
    Mikkelsen, R. F.
    Sorensen, J. N.
    Comparison between experiments and Large-Eddy Simulations of tip spiral structure and geometry2015Ingår i: Wake Conference 2015, 2015, s. 012018-, artikel-id 012018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Results from Large-Eddy Simulations using the actuator line technique have been validated against experimental results. The experimental rotor wake, which forms the basis for the comparison, was studied in a recirculating free-surface water channel, where a helical vortex was generated by a single-bladed rotor mounted on a shaft. An investigation of how the experimental blade geometry and aerofoil characteristics affect the results was performed. Based on this, an adjustment of the pitch setting was introduced, which is still well within the limits of the experimental uncertainty. Excellent agreement between the experimental and the numerical results was achieved concerning the circulation, wake expansion and pitch of the helical tip vortex. A disagreement was found regarding the root vortex position and the axial velocity along the centre line of the tip vortex. This work establishes a good base for further studies of more fundamental stability parameters of helical rotor wakes.

  • 18.
    Ivanell, Stefan
    et al.
    Högskolan på Gotland, Institutionen för kultur, energi och miljö. Kungliga Tekniska högskolan.
    Nilsson, Karl
    Kungliga Tekniska högskolan.
    Mikkelsen, Robert
    Technical University of Denmark.
    A technical Note - Methods used in wake simulations of floating turbines2012Rapport (Övrigt vetenskapligt)
  • 19.
    Ivanell, Stefan
    et al.
    Högskolan på Gotland, Institutionen för kultur, energi och miljö. Kungliga Tekniska högskolan.
    Sørensen, Jens
    Technical University of Denmark.
    Mikkelsen, Robert
    Technical University of Denmark.
    Troldborg, N.
    Technical University of Denmark.
    Okulov, V.
    Technical University of Denmark.
    Simulation and Modelling of Turbulent Wind Fields in Wind Farms: DTU Mechanical Engineering contribution to TOPFARM Work Package 12011Rapport (Övrigt vetenskapligt)
  • 20.
    Kleusberg, E.
    et al.
    Royal Inst Technol, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish E Sci Res Ctr SeRC, KTH Mech, SE-10044 Stockholm, Sweden.
    Mikkelsen, R. F.
    Tech Univ Denmark, DTU Wind Energy, DK-2800 Lyngby, Denmark.
    Schlatter, P.
    Royal Inst Technol, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish E Sci Res Ctr SeRC, KTH Mech, SE-10044 Stockholm, Sweden.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper. Royal Inst Technol, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish E Sci Res Ctr SeRC, KTH Mech, SE-10044 Stockholm, Sweden.
    Henningson, D. S.
    Royal Inst Technol, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish E Sci Res Ctr SeRC, KTH Mech, SE-10044 Stockholm, Sweden.
    High-Order Numerical Simulations of Wind Turbine Wakes2017Ingår i: WAKE CONFERENCE 2017, IOP PUBLISHING LTD , 2017, artikel-id 012025Konferensbidrag (Refereegranskat)
    Abstract [en]

    Previous attempts to describe the structure of wind turbine wakes and their mutual interaction were mostly limited to large-eddy and Reynolds-averaged Navier Stokes simulations using finite volume solvers. We employ the higher-order spectral-element code Nek5000 to study the influence of numerical aspects on the prediction of the wind turbine wake structure and the wake interaction between two turbines. The spectral-element method enables an accurate representation of the vortical structures, with lower numerical dissipation than the more commonly used finite-volume codes. The wind-turbine blades are modeled as body forces using the actuator-line method (ACL) in the incompressible Navier Stokes equations. Both tower and nacelle are represented with appropriate body forces. An inflow boundary condition is used which emulates homogeneous isotropic turbulence of wind-tunnel flows. We validate the implementation with results from experimental campaigns undertaken at the Norwegian University of Science and Technology (NTNU Blind Tests), investigate parametric influences and compare computational aspects with existing numerical simulations. In general the results show good agreement between the experiments and the numerical simulations both for a single turbine setup as well as a two-turbine setup where the turbines are offset in the spanwise direction. A shift in the wake center caused by the tower wake is detected similar to experiments. The additional velocity deficit caused by the tower agrees well with the experimental data. The wake is captured well by Nek5000 in comparison with experiments both for the single wind turbine and in the two-turbine setup. The blade loading however shows large discrepancies for the high-turbulence, two-turbine case. While the experiments predicted higher thrust for the downstream turbine than for the upstream turbine, the opposite case was observed in Nek5000.

  • 21.
    Mann, J.
    et al.
    Tech Univ Denmark, Roskilde, Denmark..
    Angelou, N.
    Tech Univ Denmark, Roskilde, Denmark..
    Arnqvist, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Callies, D.
    Fraunhofer Inst Wind Energy & Energy Syst Tech IW, Kassel, Germany..
    Cantero, E.
    Natl Renewable Energy Ctr CENER, Sarriguren, Spain..
    Arroyo, R. Chavez
    Natl Renewable Energy Ctr CENER, Sarriguren, Spain..
    Courtney, M.
    Tech Univ Denmark, Roskilde, Denmark..
    Cuxart, J.
    Univ Les Illes Balears, Mallorca, Spain..
    Dellwik, E.
    Tech Univ Denmark, Roskilde, Denmark..
    Gottschall, J.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Kuehn, P.
    Fraunhofer Inst Wind Energy & Energy Syst Tech IW, Kassel, Germany..
    Lea, G.
    Tech Univ Denmark, Roskilde, Denmark..
    Matos, J. C.
    Inst Ciencia & Inovacao Engn Mecan & Gestao Ind I, Oporto, Portugal..
    Palma, J. M. L. M.
    Univ Porto, Fac Engn, Oporto, Portugal..
    Pauscher, L.
    Fraunhofer Inst Wind Energy & Energy Syst Tech IW, Kassel, Germany..
    Pena, A.
    Tech Univ Denmark, Roskilde, Denmark..
    Rodrigo, J. Sanz
    Natl Renewable Energy Ctr CENER, Sarriguren, Spain..
    Soederberg, S.
    WeatherTech Scandinavia AB, Uppsala, Sweden..
    Vasiljevic, N.
    Tech Univ Denmark, Roskilde, Denmark..
    Rodrigues, C. Veiga
    Univ Porto, Fac Engn, Oporto, Portugal..
    Complex terrain experiments in the New European Wind Atlas2017Ingår i: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 375, nr 2091, s. 1-23, artikel-id 20160101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The New European Wind Atlas project will create a freely accessible wind atlas covering Europe and Turkey, develop the model chain to create the atlas and perform a series of experiments on flow in many different kinds of complex terrain to validate the models. This paper describes the experiments of which some are nearly completed while others are in the planning stage. All experiments focus on the flow properties that are relevant for wind turbines, so the main focus is the mean flow and the turbulence at heights between 40 and 300 m. Also extreme winds, wind shear and veer, and diurnal and seasonal variations of the wind are of interest. Common to all the experiments is the use of Doppler lidar systems to supplement and in some cases replace completely meteorological towers. Many of the lidars will be equipped with scan heads that will allow for arbitrary scan patterns by several synchronized systems. Two pilot experiments, one in Portugal and one in Germany, show the value of using multiple synchronized, scanning lidar, both in terms of the accuracy of the measurements and the atmospheric physical processes that can be studied. The experimental data will be used for validation of atmospheric flow models and will by the end of the project be freely available. This article is part of the themed issue 'Wind energy in complex terrains'.

  • 22.
    Martinen, Silke
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Carlén, Ingemar
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Analysis of the effect of curtailment on power and fatigue loads of two aligned wind turbines using an actuator disc approach2014Ingår i: Science of Making Torque from Wind, 2014, s. 012182-Konferensbidrag (Refereegranskat)
    Abstract [en]

    To study the effects of curtailment on both power production and fatigue loading, actuator disc (ACD) simulations of two turbines aligned in the wind direction are performed with the EllipSys3D code developed at DTU/Risø. Blade forces, extracted along a line that rotates in the rotor plane with the rotational velocity of the respective turbine, are used to calculate flapwise bending moments. After applying a rainflow counting algorithm an equivalent moment is calculated. Power curtailment is introduced by changing the pitch angle of the first turbine. Evaluation is made with regards to load reduction at the second turbine and to total production loss compared to the situation without any curtailment. The aeroelastic code Vidyn, developed by Teknikgruppen (Ganander [20]), is used to validate the above-mentioned ACD-based load calculation method. For this purpose, the EllipSys3D simulations are also performed without the second turbine and time series of cross sectional velocity fields are extracted at positions corresponding to the placement of the downstream turbine tested above. These fields are later used as an input for the simulations performed with Vidyn. The results from Vidyn and the results based on the ACD blade forces show similar trends. Fatigue loads at the downwind turbine are clearly decreasing as the blade pitch angle of the upstream turbine is increasing. The achievable amount of fatigue load reduction depends on the level of the imposed pre- generated turbulence as well as the spacing between the turbines. The presented method is intended for further development of wind park optimization strategies.

  • 23.
    Nilsson, Karl
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Sørensen, Jens Nørkær
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Airfoil data sensitivity analysis for actuator disc simulations used in wind turbine applications2014Ingår i: Science of Making Torque from Wind, 2014, s. 012135-Konferensbidrag (Refereegranskat)
    Abstract [en]

    To analyse the sensitivity of blade geometry and airfoil characteristics on the prediction of performance characteristics of wind farms, large-eddy simulations using an actuator disc (ACD) method are performed for three different blade/airfoil configurations. The aim of the study is to determine how the mean characteristics of wake flow, mean power production and thrust depend on the choice of airfoil data and blade geometry. In order to simulate realistic conditions, pre-generated turbulence and wind shear are imposed in the computational domain. Using three different turbulence intensities and varying the spacing between the turbines, the flow around 4-8 aligned turbines is simulated. The analysis is based on normalized mean streamwise velocity, turbulence intensity, relative mean power production and thrust. From the computations it can be concluded that the actual airfoil characteristics and blade geometry only are of importance at very low inflow turbulence. At realistic turbulence conditions for an atmospheric boundary layer the specific blade characteristics play an minor role on power performance and the resulting wake characteristics. The results therefore give a hint that the choice of airfoil data in ACD simulations is not crucial if the intention of the simulations is to compute mean wake characteristics using a turbulent inflow.

  • 24.
    Nilsson, Karl
    et al.
    Kungliga Tekniska högskolan.
    Ivanell, Stefan
    Högskolan på Gotland, Institutionen för kultur, energi och miljö. Kungliga Tekniska högskolan.
    Power estimation of the Lillgrund Wind farm using different actuator disc approaches - A base line case study2012Rapport (Övrigt vetenskapligt)
  • 25.
    Nilsson, Karl
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Mikkelsen, Robert
    Technical University of Denmark.
    Hansen, K.S.
    Technical University of Denmark.
    Sørensen, Jens Nørkær
    Technical University of Denmark.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Henningson, D.
    Technical University of Denmark.
    Large-eddy simulations of the Lillgrund wind farm2015Ingår i: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 18, nr 3, s. 449-467Artikel i tidskrift (Refereegranskat)
    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.

  • 26.
    Nilsson, Karl
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Shen, Wen Z.
    Sorensen, Jens N.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Validation of the actuator line method using near wake measurements of the MEXICO rotor2015Ingår i: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 18, nr 3, s. 499-514Artikel i tidskrift (Refereegranskat)
    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 . Copyright (c) 2014 John Wiley & Sons, Ltd.

  • 27.
    Nilsson, Karl
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Soares, José
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Energy transition Gotland: Renewable resources and system effects2018Rapport (Övrigt vetenskapligt)
  • 28.
    Olivares-Espinosa, Hugo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper. Ecole Technol Super, Dept Mech Engn, 1100 Notre Dame Ouest, Montreal, PQ H3C 1K3, Canada.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper. Nergica, 70 Rue Bolduc, Gaspe, PQ G4X 1G2, Canada.
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Masson, Christian
    Ecole Technol Super, Dept Mech Engn, 1100 Notre Dame Ouest, Montreal, PQ H3C 1K3, Canada.
    Dufresne, Louis
    Ecole Technol Super, Dept Mech Engn, 1100 Notre Dame Ouest, Montreal, PQ H3C 1K3, Canada.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Assessment of Turbulence Modelling in the Wake of an Actuator Disk with a Decaying Turbulence Inflow2018Ingår i: Applied Sciences, E-ISSN 2076-3417, Vol. 8, nr 9, artikel-id 1530Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The characteristics of the turbulence field in the wake produced by a wind turbine model are studied. To this aim, a methodology is developed and applied to replicate wake measurements obtained in a decaying homogeneous turbulence inflow produced by a wind tunnel. In this method, a synthetic turbulence field is generated to be employed as an inflow of Large-Eddy Simulations performed to model the flow development of the decaying turbulence as well as the wake flow behind an actuator disk. The implementation is carried out on the OpenFOAM platform, resembling a well-documented procedure used for wake flow simulations. The proposed methodology is validated by comparing with experimental results, for two levels of turbulence at inflow and disks with two different porosities. It is found that mean velocities and turbulent kinetic energy behind the disk are well estimated. The development of turbulence lengthscales behind the disk resembles what is observed in the free flow, predicting the ambient turbulence lengthscales to dominate across the wake, with little effect of shear from the wake envelope. However, observations of the power spectra confirm that shear yields a boost to the turbulence energy within the wake noticeable only in the low turbulence case. The results obtained show that the present implementation can successfully be used in the modelling and analysis of turbulence in wake flows.

  • 29.
    Olivares-Espinosa, Hugo
    et al.
    École de technologie supérieure, Department of Mechanical Engineering, Montréal, Canada.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Masson, Christian
    École de technologie supérieure, Department of Mechanical Engineering, Montréal, Canada.
    Dufresne, Louis
    École de technologie supérieure, Department of Mechanical Engineering, Montréal, Canada.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Characterization of wind turbine wakes in a non-sheared turbulent flow2013Ingår i: Proceedings of the 2013 International Conference on Aerodynamics of Offshore Wind Energy Systems and Wakes (ICOWES2013), Denmark, 2013, s. 435-449Konferensbidrag (Refereegranskat)
    Abstract [en]

    The characteristics of the turbulence field in wakes produced by horizontal-axis wind turbines under a uniform inflow are studied. To this aim, LES simulations of a rotor subjected to different types of inflow are performed with OpenFOAM. Two different Actuator Disk (AD) models for the rotor are implemented with the goal of assessing their capabilities to reproduce the turbulence characteristics of the wake: a uniformly loaded rotor and an AD model based on the blade element theory that employs tabulated airfoil data to calculate the distribution of forces over the disk as well as the geometry and other physical parameters from a conceptual 5 MW offshore wind turbine. The latter AD implementation makes use of a control system to adjust the rotational velocity of the rotor to the conditions of the wind flow.

    The turbulent wakes produced by the two AD models are analyzed over three different inflow conditions: laminar and two turbulent inflows of intensities 3.2 % and 6.7 % measured at the location of the rotor when the turbine is not present. The turbulence is pre-generated using the Mann model, that produces turbulent fields with the same second order statistics of the atmospheric turbulence. The turbulence is introduced in the computational domain at a position ahead of the rotor instead of at the inlet, to minimize its decay as it is convected downstream in the domain.

    A study of the turbulence evolution in the absence of the rotor reveals a discrepancy between the values of the turbulence intensity of the pre-generated field when it is measured before and after it has been introduced in the computational domain. This in turn suggests a numerical issue caused by imposing a turbulent velocity field in the flow. However, once the turbulence is introduced, it is found to exhibit a very small decay as the flow moves downstream.

    The simulations of the turbulent wake show differences in the turbulence characteristics of the near wake of each AD model. We also observe a dissimilar behaviour of the turbulence intensity along the wake for the different inflow conditions which difficult the task of determining a conclusive trend. Nonetheless, the results show that the turbulence characteristics in the far wake are nearly independent of the AD model or the inflow turbulence characteristics.

    This new implementation of the AD techniques and the use of the Mann method in OpenFOAM can be also proved useful in the future when comparing with the results of similar studies for which other CFD platforms are used.

  • 30.
    Polatidis, Heracles
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Micro-siting/positioning of wind turbines: introducing a multi-criteria decision analysis framework2014Ingår i: 7th International Multi-Conference on Engineering and Technological Innovation: Proceedings / [ed] Nagib Callos, Hsing-Wei Chu, Belkis Sánchez, Michael Savoie, Andrés Tremante, 2014, s. 23-27Konferensbidrag (Refereegranskat)
  • 31. Sarmast, Sasan
    et al.
    Dadfar, Reza
    Mikkelsen, Robert F.
    Schlatter, Philipp
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Sorensen, Jens N.
    Henningson, Dan S.
    Mutual inductance instability of the tip vortices behind a wind turbine2014Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 755, s. 705-731Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two modal decomposition techniques are employed to analyse the stability of wind turbine wakes. A numerical study on a single wind turbine wake is carried out focusing on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier-Stokes equations using the actuator line (ACL) method to simulate the wake behind the Tj ae reborg wind turbine. The wake is perturbed by low-amplitude excitation sources located in the neighbourhood of the tip spirals. The amplification of the waves travelling along the spiral triggers instabilities, leading to breakdown of the wake. Based on the grid configurations and the type of excitations, two basic flow cases, symmetric and asymmetric, are identified. In the symmetric setup, we impose a 120 degrees symmetry condition in the dynamics of the flow and in the asymmetric setup we calculate the full 360 degrees wake. Different cases are subsequently analysed using dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD). The results reveal that the main instability mechanism is dispersive and that the modal growth in the symmetric setup arises only for some specific frequencies and spatial structures, e.g. two dominant groups of modes with positive growth (spatial structures) are identified, while breaking the symmetry reveals that almost all the modes have positive growth rate. In both setups, the most unstable modes have a non-dimensional spatial growth rate close to pi/2 and they are characterized by an out-of-phase displacement of successive helix turns leading to local vortex pairing. The present results indicate that the asymmetric case is crucial to study, as the stability characteristics of the flow change significantly compared to the symmetric configurations. Based on the constant non-dimensional growth rate of disturbances, we derive a new analytical relationship between the length of the wake up to the turbulent breakdown and the operating conditions of a wind turbine.

  • 32.
    Sarmast, Sasan
    et al.
    Tech Univ Denmark, DTU Wind Energy, Bldg 101A, DK-2800 Lyngby, Denmark.;Royal Inst Technol, KTH Mech, Linne FLOW Ctr, Swedish E Sci Res Ctr SeRC, Stockholm, Sweden..
    Segalini, Antonio
    Royal Inst Technol, KTH Mech, Linne FLOW Ctr, Swedish E Sci Res Ctr SeRC, Stockholm, Sweden..
    Mikkelsen, Robert F.
    Tech Univ Denmark, DTU Wind Energy, Bldg 101A, DK-2800 Lyngby, Denmark..
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper. Royal Inst Technol, KTH Mech, Linne FLOW Ctr, Swedish E Sci Res Ctr SeRC, Stockholm, Sweden..
    Comparison of the near-wake between actuator-line simulations and a simplified vortex model of a horizontal-axis wind turbine2016Ingår i: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 19, nr 3, s. 471-481Artikel i tidskrift (Refereegranskat)
    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.

  • 33.
    Simisiroglou, Nikolaos
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Gravdahl, Arne
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Description and validation of the actuator disc approach in PHOENICS.2016Rapport (Övrig (populärvetenskap, debatt, mm))
  • 34.
    Simisiroglou, Nikolaos
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Validation of the actuator disc approach using small-scale model wind turbines2017Ingår i: Wind Energy Science, ISSN 2213-3968, E-ISSN 2366-7443, Vol. 2, s. 587-601Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the present study is the validation of the implementation of an actuator disc (ACD) model in the computational fluid dynamics (CFD) code PHOENICS. The flow behaviour for three wind turbine cases is investigated numerically and compared to wind tunnel measurements: (A) the flow around a single model wind turbine, (B) the wake interaction between two in-line model wind turbines for a uniform inflow of low turbulence intensity and (C) the wake interaction between two in-line model wind turbines at different separation distances in a uniform or sheared inflow of high turbulence intensity. This is carried out using Reynolds-averaged Navier–Stokes (RANS) simulations and an ACD technique in the CFD code PHOENICS. The computations are conducted for the design condition of the rotors using four different turbulence closure models and five different thrust distributions. The computed axial velocity field as well as the turbulence kinetic energy are compared with hot-wire anemometry (HWA) measurements. For the cases with two in-line wind turbines, the thrust coefficient is also computed and compared with measurements. The results show that for different inflow conditions and wind turbine spacings the proposed method is able to predict the overall behaviour of the flow with low computational effort. When using the k-ε and Kato–Launder k-ε turbulence models the results are generally in closer agreement with the measurements.

  • 35.
    Simisiroglou, Nikolaos
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära. WindSim AS, Fjordgaten 15, N-3125 Tonsberg, Norway.
    Karatsioris, Michael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Nilsson, Karl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Breton, Simon-Philippe
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    The actuator disc concept in PHOENICS2016Ingår i: Energy Procedia / [ed] Tande, JOG; Kvamsdal, T; Muskulus, M, 2016, Vol. 94, s. 269-277Konferensbidrag (Refereegranskat)
    Abstract [en]

    This study presents two models to simulate a wind turbine. This is done by employing the 1D momentum actuator disc theory in PHOENICS, a general purpose computational fluid dynamics software. To test the general applicability of these models, single wind turbine simulations are conducted using eight different wind turbine models from two manufacturers. The simulations are performed by imposing sheared inflow with hub height wind speeds ranging from 3 m/s up to 25 m/s. A range of computational parameters are investigated, including the resolution of the domain, the thickness of the actuator disc and the iterative convergence criteria. To investigate the wake development produced by these methods, a comparison study is performed with the more complex large-eddy simulation software EllipSys3D using an actuator disc approach for validation purposes. The resulting wind turbine thrust and power outputs from PHOENICS are compared with the experimental power curves and thrust values provided by the manufacturers for each wind turbine. The results show that actuator disc methods are able to provide a reasonable estimation of the conventional wind turbine power and thrust output with low computational effort. Moreover, the results from the preliminary comparison of the wake produced from these two rotor models compare well with the wake produced by the actuator disc in EllipSys3D.

  • 36.
    Simisiroglou, Nikolaos
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära. WindSim AS, Tønsberg , Norway.
    Polatidis, Heracles
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Wind farm power production assessment: a comparative analysis of two actuator disc methods and two analytical wake models2018Ingår i: Wind Energy Science, ISSN 2213-3968, E-ISSN 2366-7443, Vol. 2018, s. 1-13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the present study is to perform a comparative analysis of two actuator disc methods (ACD) and two analytical wake models for wind farm power production assessment. To do so wind turbine power production data from the Lillgrund offshore wind farm in Sweden is used. The measured power production for individual wind turbines is compared with results from simulations, done in the WindSim software, using two ACD methods (old and new) and two analytical wake models widely used within the wind industry (Jensen and Larsen wake models). It was found that the new ACD method and the Larsen model outperform the other method and model in most cases. Furthermore, results from the new ACD method show a clear improvement in the estimated power production in comparison to the old ACD method. The Jensen method seems to overestimate the power deficit for all cases. The new ACD method, despite it's simplicity, is capable of capturing the power production within the given error margin although it tends to underestimate the power deficit.

  • 37.
    Simisiroglou, Nikolaos
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära. WindS AS, Fjordgaten 15, N-3125 Tonsberg, Norway.
    Polatidis, Heracles
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Wind Farm Power Production Assessment: Introduction of a New Actuator Disc Method and Comparison with Existing Models in the Context of a Case Study2019Ingår i: Applied Sciences, E-ISSN 2076-3417, Vol. 9, nr 3, artikel-id 431Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the present study is to perform a comparative analysis of two actuator disc methods (ACD) and two analytical wake models for wind farm power production assessment. To do so, wind turbine power production data from the Lillgrund offshore wind farm in Sweden is used. The measured power production for individual wind turbines is compared with results from simulations, done in the WindSim software, using two ACD methods (ACD (2008) and ACD (2016)) and two analytical wake models widely used within the wind industry (Jensen and Larsen wake models). It was found that the ACD (2016) method and the Larsen model outperform the other method and model in most cases. Furthermore, results from the ACD (2016) method show a clear improvement in the estimated power production in comparison to the ACD (2008) method. The Jensen method seems to overestimate the power deficit for all cases. The ACD (2016) method, despite its simplicity, can capture the power production within the given error margin although it tends to underestimate the power deficit.

  • 38.
    Sörensen, Jens N.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Mikkelsen, Robert F.
    Henningson, Dan S.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Sarmast, Sasan
    Andersen, Soren J.
    Simulation of wind turbine wakes using the actuator line technique2015Ingår i: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 373, nr 2035, s. 20140071-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake.

  • 39.
    Sörensen, Jens
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper. Technical University of Denmark.
    Sarmast, S.
    KTH Royal Institute of Technology.
    Mikkelsen, Robert
    Technical University of Denmark.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Henningson, D.
    Technical University of Denmark.
    Determination of Wind Turbine Near-Wake Length Based on Stability Analysis2014Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 524, s. 012155-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A numerical study on the wake behind a wind turbine is carried outfocusing on determining the length of the near-wake based on the instability onset ofthe trailing tip vortices shed from the turbine blades. The numerical model is based onlarge-eddy simulations (LES) of the Navier-Stokes equations using the actuator line(ACL) method. The wake is perturbed by applying stochastic or harmonic excitations inthe neighborhood of the tips of the blades. The flow field is then analyzed to obtain thestability properties of the tip vortices in the wake of the wind turbine. As a mainoutcome of the study it is found that the amplification of specific waves (travelingstructures) along the tip vortex spirals is responsible for triggering the instabilityleading to wake breakdown. The presence of unstable modes in the wake is related tothe mutual inductance (vortex pairing) instability where there is an out-of-phasedisplacement of successive helix turns. Furthermore, using the non-dimensional growthrate, it is found that the pairing instability has a universal growth rate equal to π/2.Using this relationship, and the assumption that breakdown to turbulence occurs once avortex has experienced sufficient growth, we provide an analytical relationship betweenthe turbulence intensity and the stable wake length. The analysis leads to a simpleexpression for determining the length of the near wake. This expression shows that thenear wake length is inversely proportional to thrust, tip speed ratio and the logarithmicof the turbulence intensity

  • 40. van Kuik, Gijs
    et al.
    Yu, Wei
    Sarmast, Sasan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Ivanell, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Comparison of actuator disc and Joukowsky rotor flows, to explore the need for a tip correction2015Ingår i: Wake Conference 2015, 2015, s. 012013-, artikel-id 012013Konferensbidrag (Refereegranskat)
    Abstract [en]

    In van Kuik & Lignarolo (2015, Wind Energy accepted with modifications) potential flow solutions have been obtained for classical actuator discs (axisymmetric, uniform load) presenting a model for the non-uniformity of the axial velocity at the disc. Current rotor design models proceed from a disc with a uniform axial velocity, modified by a tip correction like the one of Prandtl-Glauert-Shen. A comparison shows that this correction leads to a similar distribution as obtained from the potential flow solutions. A next comparison is made with the velocity distribution at the blade position of a Joukowsky rotor with constant bound circulation, calculated by an Actuator Line and a Lifting Line model. The resulting distributions correspond reasonably well to the potential flow disc distribution, in magnitude as well as shape. This implies that this non-uniform distribution is relevant for a rotor with a finite number of blades, and could be the basis for rotor design instead of the uniform but tip-corrected distribution.

  • 41. Vogstad, Klaus
    et al.
    Bhutoria, Vaibhav
    Amund Lund, John
    Ivanell, Stefan
    Högskolan på Gotland, Institutionen för kultur, energi och miljö.
    Uzunoglu, Bahri
    Högskolan på Gotland, Institutionen för kultur, energi och miljö.
    Instant Wind: Model reduction for fast CFD computations2012Rapport (Övrigt vetenskapligt)
1 - 41 av 41
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