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  • 1.
    Kleine, Vitor
    et al.
    KTH, Skolan för teknikvetenskap (SCI).
    Kleusberg, ElektraKTH, Skolan för teknikvetenskap (SCI).Hanifi, ArdeshirKTH, Skolan för teknikvetenskap (SCI).Henningson, Dan S.KTH, Skolan för teknikvetenskap (SCI).
    Tip-vortex instabilities of two in-line wind turbines2019Proceedings (redaktörskap) (Refereegranskat)
  • 2.
    Kleine, Vitor
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. Instituto Tecnológico de Aeronáutica, Praça Marechal Eduardo Gomes, 50, Vila das Acácias, São Josédos Campos SP, 12228-900, Brazil.
    Kleusberg, Elektra
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Hanifi, Ardeshir
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Tip-vortex instabilities of two in-line wind turbines2019Ingår i: Wake Conference 201922–24 May 2019, Visby, Sweden, Institute of Physics Publishing (IOPP), 2019, Vol. 1256, nr 1, artikel-id 012015Konferensbidrag (Refereegranskat)
    Abstract [en]

    The hydrodynamic stability of a vortex system behind two in-line wind turbines operating at low tip-speed ratios is investigated using the actuator-line method in conjunction with the spectral-element flow solver Nek5000. To this end, a simplified setup with two identical wind turbine geometries rotating at the same tip-speed ratio is simulated and compared with a single turbine wake. Using the rotating frame of reference, a steady solution is obtained, which serves as a base state to study the growth mechanisms of induced perturbations to the system. It is shown that, already in the steady state, the tip vortices of the two turbines interact with each other, exhibiting the so-called overtaking phenomenon. Hereby, the tip vortices of the upstream turbine overtake those of the downstream turbine repeatedly. By applying targeted harmonic excitations at the upstream turbine's blade tips a variety of modes are excited and grow with downstream distance. Dynamic mode decomposition of this perturbed flow field showed that the unstable out-of-phase mode is dominant, both with and without the presence of the second turbine. The perturbations of the upstream turbine's helical vortex system led to the destabilization of the tip vortices shed by the downstream turbine. Two distinct mechanisms were observed: for certain frequencies the downstream turbine's vortices oscillate in phase with the vortex system of the upstream turbine while for other frequencies a clear out-of-phase behaviour is observed. Further, short-wave instabilities were shown to grow in the numerical simulations, similar to existing experimental studies [1].

  • 3.
    Kleusberg, Elektra
    KTH, Skolan för teknikvetenskap (SCI).
    Parametric study of the actuator-line method in high-order codes2019Rapport (Övrigt vetenskapligt)
  • 4.
    Kleusberg, Elektra
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    Wind turbine simulations using spectral elements2017Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Understanding the flow around wind turbines is a highly relevant research question due to the increased interest in harvesting energy from renewable sources. This thesis approaches the topic by means of numerical simulations using the actuator line method and the incompressible Navier–Stokes equations in the spectral element code Nek5000. The aim is to gain enhanced understanding of the wind turbine wake structure and wind turbine wake interaction. A verification study of the method and implementation is performed against the finite volume solver EllipSys3D using two types of turbines, an idealized constant circulation turbine and the Tjæreborg turbine. It is shown that Nek5000 requires significantly lower resolution to accurately compute the wake development, however, at the cost of a smaller time step.The constant circulation turbine is investigated further with the goal of establishing guidelines for the use of the actuator line method in spectral element codes, where the mesh is inherently non-equidistant and currently used guidelines of force distribution based on Gaussian kernels are difficult to apply. It is shown that Nek5000 requires a larger kernel width in the fixed frame of reference to remove numerical instabilities. Further, the impact of different Gaussian widths on the wake development is investigated in the rotating frame of reference, showing that the convection velocity and the breakdown of the spiral tip and root vortices are dependent on the Gaussian width. In the second part, the flow around single and multiple wind-turbine setups at different operating conditions is investigated and compared with experimental results. The focus is placed on comparing the power and thrust coefficients and the wake development based on the time-averaged streamwise velocity and turbulent stresses. Further the influence of the tower model is investigated both upstream and downstream of the turbine. The results show that the wake is captured accurately in most cases. The loading exhibits a significant dependence on the Reynolds number at which the airfoil data is extracted. When the helical tip vortices are stable the turbulent stresses at the tip vortices are underestimated in the numerical simulations. This is due to the finite resolution and the projection of the actuator line forces in the numerical domain using a prescribed Gaussian width, which leads to lower induced velocities in the helical vortices.

  • 5.
    Kleusberg, Elektra
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    Wind-turbine wakes - Effects of yaw, shear and turbine interaction2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Den så kallade actuator line-metoden används tillsammans med inkompressibla Navier–Stokes ekvationer för att undersöka strömningens utveckling bakom vindturbiner. Inledande studier syftar till att utförligt validera implementationen i spektralelementkoden Nek5000 mot befintliga numeriska och experimentella datamängder. Det visas att den nuvarande implementationen ger en noggrann representation av strömningsfältet för alla undersökta turbingeometrier. Vidare fångas utvecklingen hos vaken väl för en rad olika inflödesvillkor, förturbingirning, och under interaktion mellan flera turbiner.

    Vakutvecklingen för en girad turbin visas bero signifikant på kvoten mellan vingspetsens och friströmmens hastighet, både när det gäller hastighetsunderskottet i vaken och bildningen av de motroterande vakvirvlarna. För låga hastighetskvoter mellan vingspetsen och friströmmen uppvisar vakens hastighetsunderskott en betydande asymmetri med avseende på horisontalplanet genom en så kallad avancerande/retirerande effekt. För höga hastighetskvoter blir denna effekt däremot försumbar i jämförelse med vakens skevhet som påverkar symmetrin med avseende på vertikalplanet. Dessa inhomogeniteter i den medelvärdesbildade vakutvecklingen påverkar också det turbulenta nedbrottet hos vingspetsvirvlarna, vilket inträffar vid olika positioner i vinkelled på grund av signifikanta vinkelvariationer hos virvelstyrkan och konvektionshastigheten. En analys of interaktionen mellan en girad turbinvak och en inkommande skjuvströmning avslöjar ett beroende hos vakens förskjutning och återhämtning på girningens riktning, vilket resulterar i betydande skillnader i den sammantagna effekten hos två turbiner. Mer detaljerade studier av spetsvirvlarnas nedbrott i skjuvströmningar med enfrekvensstörningar visar att ett skjuvat inflöde förändrar den spatiella tillväxtgraden längs den vertikala axeln på grund av varierande konvektionshastighet hos spetsvirvlarna.Tillväxtgraderna sammanfaller dock med motsvarande värde för det klassiska fallet med två oändliga virvelrader, om de skalas med lokala virvelparametrar. Slutligen studeras en stationär virvelutveckling för ett idealiserat fall bestående av två turbiner i linje med varandra. Genom att applicera en rad kontrollerade störningar, exciteras moder som beroende på frekvens uppvisar förskjutningar i eller ur fas med virvelsystemen från turbinen uppströms och nedströms.

  • 6.
    Kleusberg, Elektra
    et al.
    KTH, Skolan för teknikvetenskap (SCI).
    Benard, Sabrina
    KTH, Skolan för teknikvetenskap (SCI).
    Henningson, Dan
    KTH, Skolan för teknikvetenskap (SCI).
    Tip-vortex breakdown of wind turbines subject to shearManuskript (preprint) (Övrigt vetenskapligt)
  • 7.
    Kleusberg, Elektra
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Benard, Sabrina
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. Ecole Normale Supérieure Paris-Saclay, Cachan, France.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Tip-vortex breakdown of wind turbines subject to shear2019Ingår i: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, nr 12, s. 1789-1799Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sheared velocity profiles pervade all wind-turbine applications, thus making it important to understand their effect on the wake. In this study, a single wind turbine is modeled using the actuator-line method in the incompressible Navier–Stokes equations. The tip vortices are perturbed harmonically, and the growth rate of the response is evaluated under uniform inflow and a linear velocity profile. Whereas previous investigations of this kind were conducted in the rotating frame of reference, this study evaluates the excitation response in the fixed frame of reference, thus necessitating a frequency transformation. It is shown that increasing the shear decreases the spatial growth rate in the upper half of the wake while increasing it in the lower half. When scaled with the local tip vortex parameters, the growth rate along the entire azimuth collapses to a single value for the investigated wavenumbers. We conclude that even though the tip-vortex breakdown is asymmetric in sheared flow, the scaled growth rates follow the behavior of axisymmetric helical vortices. An excitation amplitude reduction by an order of magnitude extends the linear growth region of the wake by one radius for uniform inflow. In the sheared setup, the linear growth region is extended further in the top half than in the bottom half because of the progressive distortion of the helical tip vortices. An existing model to determine the stable wake length was shown to be in close agreement with the observed numerical results when adjusted for shear.

  • 8.
    Kleusberg, Elektra
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Mikkelsen, R. F.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Ivanell, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    High-Order Numerical Simulations of Wind Turbine Wakes2017Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 854, nr 1, artikel-id 012025Artikel i tidskrift (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.

  • 9.
    Kleusberg, Elektra
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    Mikkelsen, Robert
    Danish Technical University .
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Ivanell, Stefan
    Uppsala University.
    Henningson, Dan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    High-order numerical simulations of wind turbine wakes2017Rapport (Övrigt vetenskapligt)
    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 much lower numerical dissipation than the more commonly used finite volume codes. The 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 the 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, investigate parametric influences and compare computational aspects with the existing finite volume codes. The results show good agreement between the experiments and the numerical simulations.

  • 10.
    Kleusberg, Elektra
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Sarmast, S.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Ivanell, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Uppsala University, Wind Energy Section, Campus Gotland, SE-621 67 Visby, Sweden.
    Henningson, Dan Stefan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Actuator line simulations of a Joukowsky and Tjæreborg rotor using spectral element and finite volume methods2016Ingår i: SCIENCE OF MAKING TORQUE FROM WIND (TORQUE 2016), Institute of Physics (IOP), 2016, Vol. 753, nr 8, artikel-id 082011Konferensbidrag (Refereegranskat)
    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 Tjffireborg 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.

  • 11.
    Kleusberg, Elektra
    et al.
    KTH, Skolan för teknikvetenskap (SCI).
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI).
    Henningson, Dan
    KTH, Skolan för teknikvetenskap (SCI).
    Near-wake structure of the yawed wind turbine2019Rapport (Övrigt vetenskapligt)
  • 12.
    Kleusberg, Elektra
    et al.
    KTH, Skolan för teknikvetenskap (SCI).
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI).
    Henningson, Dan
    KTH, Skolan för teknikvetenskap (SCI).
    Parametric dependencies of the yawed wind-turbine wake developmentManuskript (preprint) (Övrigt vetenskapligt)
  • 13.
    Kleusberg, Elektra
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Henningson, Dan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    Parametric study of the actuator line method in high-order codes2017Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The high accuracy of spectral element methods combined with low computationalcost and a high level of parallelization, makes them appealing for large-scale investigations of wind turbines and wind turbine interaction using the state-of-the-art actuator line method by Sørensen & Shen (2002). While the spectral element code Nek5000 has already been used for wind turbine simulations by e.g. Peet et al. (2013), Chatterjee & Peet (2015), Chatterjee & Peet (2016) and Kleusberg et al. (2016) for investigations of wind turbine wakes and wake interaction, the implications of the actuator line method in a high-order code and the effect of the involved parameters have not been studied in detail. This paper investigates the constant circulation turbine in the fixed and rotatingframe of reference. In the rotating frame of reference several wake parameters previously discussed e.g. by Ivanell et al. (2009) and Sarmast (2013) are revisitedand analyzed. Further, parametric studies are conducted in the fixed frame ofreference to investigate an observed instablility related to the spectral element width. The instablity is not a property of the spectral element discretization as it is also observed in other research using finite volume techniques. However, the decreased numerical dissipation and the non-equidistant grid used in spectral element methods leads to amplification of the instability. The parameters are investigated on a reduced two-dimensional test case and the conclusions transfered to the full actuator line setup. It is established that a Gaussian width of approximately five times the average grid spacing is necessary to reduce the effect of the instability related to the spectral element width when investigating sensitive flow cases. A force projection method proposed by Pinelli et al. (2010) is investigated as an alternative to the typically used Gaussian kernel. Finally, the influence of this instability is investigated when perturbations are applied tothe flow. Both small-scale perturbations that are introduced at the blade tips and low inflow turbulence which is imposed as an inlet condition are investigated.It is shown that when perturbations are introduced to the flow the large-scale wake behavior in the rotating and fixed frame of reference are similar and a Gaussian width which is 2.4 times the averaged grid spacing is sufficient.

  • 14.
    Kleusberg, Elektra
    et al.
    KTH, Skolan för teknikvetenskap (SCI).
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI).
    Henningson, Dan
    KTH, Skolan för teknikvetenskap (SCI).
    Yaw optimization potential of wind turbines in sheared flows.2019Rapport (Övrigt vetenskapligt)
  • 15.
    Muhle, Franz
    et al.
    Norwegian Univ Life Sci, Fac Environm Sci & Nat Resource Management, As, Norway..
    Schottler, Jannik
    Carl von Ossietzky Univ Oldenburg, ForWind Ctr Wind Energy, Inst Phys, Oldenburg, Germany..
    Bartl, Jan
    Norwegian Univ Sci & Technol, Dept Energy & Proc Engn, Trondheim, Norway..
    Futrzynski, Romain
    Siemens PLM Software, London, England..
    Evans, Steve
    Siemens PLM Software, London, England..
    Bernini, Luca
    Politecn Milan, Dept Mech Engn, Milan, Italy..
    Schito, Paolo
    Politecn Milan, Dept Mech Engn, Milan, Italy..
    Draper, Martin
    Univ Republica, Fac Ingn, Montevideo, Uruguay..
    Guggeri, Andres
    Univ Republica, Fac Ingn, Montevideo, Uruguay..
    Kleusberg, Elektra
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Holling, Michael
    Carl von Ossietzky Univ Oldenburg, ForWind Ctr Wind Energy, Inst Phys, Oldenburg, Germany..
    Peinke, Joachim
    Carl von Ossietzky Univ Oldenburg, ForWind Ctr Wind Energy, Inst Phys, Oldenburg, Germany.;Fraunhofer IWES, Oldenburg, Germany..
    Adaramola, Muyiwa S.
    Norwegian Univ Life Sci, Fac Environm Sci & Nat Resource Management, As, Norway..
    Saetran, Lars
    Norwegian Univ Sci & Technol, Dept Energy & Proc Engn, Trondheim, Norway..
    Blind test comparison on the wake behind a yawed wind turbine2018Ingår i: Wind Energy Science, ISSN 2213-3968, E-ISSN 2366-7443, Vol. 3, nr 2, s. 883-903Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article summarizes the results of the "Blind test 5" workshop, which was held in Visby, Sweden, in May 2017. This study compares the numerical predictions of the wake flow behind a model wind turbine operated in yaw to experimental wind tunnel results. Prior to the workshop, research groups were invited to predict the turbine performance and wake flow properties using computational fluid dynamics (CFD) methods. For this purpose, the power, thrust, and yaw moments for a 30 degrees yawed model turbine, as well as the wake's mean and turbulent streamwise and vertical flow components, were measured in the wind tunnel at the Norwegian University of Science and Technology (NTNU). In order to increase the complexity, a non-yawed downstream turbine was added in a second test case, while a third test case challenged the modelers with a new rotor and turbine geometry. Four participants submitted predictions using different flow solvers, three of which were based on large eddy simulations (LES) while another one used an improved delayed detached eddy simulation (IDDES) model. The performance of a single yawed turbine was fairly well predicted by all simulations, both in the first and third test cases. The scatter in the downstream turbine performance predictions in the second test case, however, was found to be significantly larger. The complex asymmetric shape of the mean streamwise and vertical velocities was generally well predicted by all the simulations for all test cases. The largest improvement with respect to previous blind tests is the good prediction of the levels of TKE in the wake, even for the complex case of yaw misalignment. These very promising results confirm the mature development stage of LES/DES simulations for wind turbine wake modeling, while competitive advantages might be obtained by faster computational methods.

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