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Träfflista för sökning "WFRF:(Sörensen Jens) ;pers:(Nilsson Karl)"

Sökning: WFRF:(Sörensen Jens) > Nilsson Karl

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  • Nilsson, Karl, et al. (författare)
  • Airfoil data sensitivity analysis for actuator disc simulations used in wind turbine applications
  • 2014
  • Ingår i: SCIENCE OF MAKING TORQUE FROM WIND 2014 (TORQUE 2014). - : IOP Publishing. ; , s. 012135-, s. 012135-
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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  • Nilsson, Karl, et al. (författare)
  • Large-eddy simulations of the Lillgrund wind farm
  • 2015
  • Ingår i: Wind Energy. - : John Wiley & Sons. - 1095-4244 .- 1099-1824. ; 18:3, s. 449-467
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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  • Nilsson, Karl, et al. (författare)
  • Validation of the actuator line method using near wake measurements of the MEXICO rotor
  • 2015
  • Ingår i: Wind Energy. - : John Wiley & Sons. - 1095-4244 .- 1099-1824. ; 18:3, s. 499-514
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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  • Sörensen, Jens Nörkaer, et al. (författare)
  • Analytical body forces in numerical actuator disc model of wind turbines
  • 2020
  • Ingår i: Renewable energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0960-1481 .- 1879-0682. ; 147:Part 1, s. 2259-2271
  • Tidskriftsartikel (refereegranskat)abstract
    • An analytical model for representing body forces in numerical actuator disc models of wind turbines is developed and validated. The model is based on the assumption that the rotor disc is subject to a constant circulation modified for tip and root effects. The model comprises expressions for both the axial and the azimuthal force distributions, and is generalized to be utilized for all kinds of inflow, including wind shear, turbulence, and shadow effects in wind farms. The advantage of the model is that it does not depend on any detailed knowledge concerning the wind turbine being analysed, but only requires knowledge regarding the rated wind speed and nameplate capacity. To validate the analytical model, results are compared to numerically generated results using detailed information regarding geometry and airfoil data for the 2 MW Tjaereborg wind turbine and the 10 MW DTU reference turbine. The comparisons show very good agreement between the loadings using the new analytical model and the airfoil data based method for the two tested wind turbines, demonstrating that the analytical model is a simple and reliable way of introducing body forces in actuator disc simulations without any prior knowledge of the wind turbine being analysed.
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  • Resultat 1-8 av 8

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