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  • 1.
    Ivanell, Stefan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Leweke, T.
    Sarmast, Sasan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Quaranta, H. U.
    Mikkelsen, R. F.
    Sorensen, J. N.
    Comparison between experiments and Large-Eddy Simulations of tip spiral structure and geometry2015In: Wake Conference 2015, 2015, p. 012018-, article id 012018Conference paper (Refereed)
    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.

  • 2.
    Kleusberg, E.
    et al.
    Royal Inst Technol, KTH Mech, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish ESci Res Ctr SeRC, SE-10044 Stockholm, Sweden.
    Sarmast, Sasan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Schlatter, P.
    Royal Inst Technol, KTH Mech, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish ESci Res Ctr SeRC, SE-10044 Stockholm, Sweden.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Royal Inst Technol, KTH Mech, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish ESci Res Ctr SeRC, SE-10044 Stockholm, Sweden.
    Henningson, D. S.
    Royal Inst Technol, KTH Mech, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish ESci Res Ctr SeRC, SE-10044 Stockholm, Sweden.
    Actuator line simulations of a Joukowsky and Tjaereborg rotor using spectral element and finite volume methods2016In: SCIENCE OF MAKING TORQUE FROM WIND (TORQUE 2016), 2016, article id 082011Conference paper (Refereed)
    Abstract [en]

    The wake structure behind a wind turbine, generated by the spectral element code Nek5000, is compared with that from the finite volume code EllipSys3D. The wind turbine blades are modeled using the actuator line method. We conduct the comparison on two different setups. One is based on an idealized rotor approximation with constant circulation imposed along the blades corresponding to Glauert's optimal operating condition, and the other is the Tjareborg wind turbine. The focus lies on analyzing the differences in the wake structures entailed by the different codes and corresponding setups. The comparisons show good agreement for the defining parameters of the wake such as the wake expansion, helix pitch and circulation of the helical vortices. Differences can be related to the lower numerical dissipation in Nek5000 and to the domain differences at the rotor center. At comparable resolution Nek5000 yields more accurate results. It is observed that in the spectral element method the helical vortices, both at the tip and root of the actuator lines, retain their initial swirl velocity distribution for a longer distance in the near wake. This results in a lower vortex core growth and larger maximum vorticity along the wake. Additionally, it is observed that the break down process of the spiral tip vortices is significantly different between the two methods, with vortex merging occurring immediately after the onset of instability in the finite volume code, while Nek5000 simulations exhibit a 2-3 radii period of vortex pairing before merging.

  • 3.
    Sarmast, Sasan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Shen, W. Z.
    Tech Univ Denmark, Wind Energy Dept, DK-2800 Lyngby, Denmark.
    Zhu, W. J.
    Tech Univ Denmark, Wind Energy Dept, DK-2800 Lyngby, Denmark.
    Mikkelsen, R. F.
    Tech Univ Denmark, Wind Energy Dept, DK-2800 Lyngby, Denmark.
    Breton, Simon-Philippe
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. KTH Mech, S-10044 Stockholm, Sweden.
    Validation of the actuator line and disc techniques using the New MEXICO measurements2016In: SCIENCE OF MAKING TORQUE FROM WIND (TORQUE 2016), 2016, article id 032026Conference paper (Refereed)
    Abstract [en]

    Actuator line and disc techniques are employed to analyse the wake obtained in the New MEXICO wind turbine experiment. The New MEXICO measurement campaign done in 2014 is a follow-up to the MEXICO campaign, which was completed in 2006. Three flow configurations in axial flow condition are simulated and both computed loads and velocity fields around the rotor are compared with detailed PIV measurements. The comparisons show that the computed loadings are generally in agreement with the measurements under the rotor's design condition. Both actuator approaches under-predicted the loading in the inboard part of blade in stall condition as only 2D airfoil data were used in the simulations. The predicted wake velocities generally agree well with the PIV measurements. In the experiment, PIV measurements are also provided close to the hub and nacelle. To study the effect of hub and nacelle, numerical simulations are performed both in the presence and absence of the hub geometry. This study shows that the large hub used in the experiment has only small effects on overall wake behaviour.

  • 4.
    Simisiroglou, Nikolaos
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. WindSim AS, Fjordgaten 15, N-3125 Tønsberg, Norway.
    Sarmast, Sasan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Breton, Simon-Philippe
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Validation of the actuator disc approach in PHOENICS using small scale model wind turbines2016In: Science Of Making Torque From Wind (Torque 2016), 2016, Vol. 753, article id 032028Conference paper (Refereed)
    Abstract [en]

    In this study two wind turbine setups are investigated numerically: (a) the flow around a single model wind turbine and (b) the wake interaction between two in-line model wind turbines. This is done by using Reynolds averaged Navier-Stokes (RANS) and an actuator disc (ACD) technique in the computational fluid dynamics code PHOENICS. The computations are conducted for the design condition of the rotors using four different turbulence closure models. The computed axial velocity field as well as the turbulent kinetic energy are compared with PIV measurements. For the two model wind turbine setup, the thrust and power coefficient are also computed and compared with measurements. The results show that this RANS ACD method is able to predict the overall behaviour of the flow with low computational effort and that the turbulence closure model has a direct effect on the predicted wake development.

  • 5. van Kuik, Gijs
    et al.
    Yu, Wei
    Sarmast, Sasan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Comparison of actuator disc and Joukowsky rotor flows, to explore the need for a tip correction2015In: Wake Conference 2015, 2015, p. 012013-, article id 012013Conference paper (Refereed)
    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.

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