Evaluation of tilt control for wind-turbine arrays in the atmospheric boundary layer

Cossu, Carlo

doi:10.5194/wes-2020-106

Cited by 5 publications

(6 citation statements)

References 54 publications

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“…The method suggested to achieve this is individual rotor yaw since it is a well‐established technique; however, the effects of rotor tilt are also of interest 51,52 and could be examined in further works. The effects of pitch and roll in floating turbines may also be applied to the multirotor case, as has been investigated in single rotor wind tunnel studies (for example, 53‐56 ) and numerical studies of Xiao and Yang 57 .…”

Section: Introductionmentioning

confidence: 99%

Wake steering of multirotor wind turbines

et al. 2021

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In this paper, wake steering is applied to multirotor turbines to determine whether it has the potential to reduce wind plant wake losses. Through application of rotor yaw to multirotor turbines, a new degree of freedom is introduced to wind farm control such that wakes can be expanded, channelled or redirected to improve inflow conditions for downstream turbines. Five different yaw configurations are investigated (including a baseline case) by employing large‐eddy simulations (LES) to generate a detailed representation of the velocity field downwind of a multirotor wind turbine. Two lower‐fidelity models from single‐rotor yaw studies (curled‐wake model and analytical Gaussian wake model) are extended to the multirotor case, and their results are compared with the LES data. For each model, the wake is analysed primarily by examining wake cross‐sections at different downwind distances. Further quantitative analysis is carried out through characterisations of wake centroids and widths over a range of streamwise locations and through a brief analysis of power production. Most significantly, it is shown that rotor yaw can have a considerable impact on both the distribution and magnitude of the wake velocity deficit, leading to power gains for downstream turbines. The lower‐fidelity models show small deviation from the LES results for specific configurations; however, both are able to reasonably capture the wake trends over a large streamwise range.

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Section: Introductionmentioning

confidence: 99%

Wake steering of multirotor wind turbines

et al. 2021

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“…the authors simulated up to three turbines in a column; both studies reported significant power gains at the cluster level, caused by an improved capture downstream that offsets more limited losses upstream. Simulation studies on more complex layouts were conducted by Cossu (2020a) and Cossu (2020b), where the front two rows of turbines in a farm were tilted, obtaining significant power gains at the wind plant level. The author also studied the effect that rotor size, longitudinal spacing between the turbines and thrust setting can have on the plant power output.…”

Section: Introductionmentioning

confidence: 99%

“…To this purpose, CFD simulations of a scaled wind turbine, validated with wind tunnel experiments, are employed. Expanding on previous tilt misalignment studies, which analyzed streamwise spacings of 6-8 rotor diameters (Fleming et al, 2015;Annoni et al, 2017;Cossu, 2020b;Scott et al, 2020), the present work considers distances up to 12 rotor diameters, which is a more realistic spacing for offshore-wind applications. -Make preliminary calculations of the quantity of water ballast that needs to be redistributed for achieving the necessary tilting of the rotor, along with estimating the associated energy expenditure.…”

mentioning

confidence: 99%

Vertical wake deflection for floating wind turbines by differential ballast control

Nanos¹,

Bottasso²,

Manolas

et al. 2021

Preprint

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Abstract. This paper presents a feasibility analysis of vertical wake steering for floating turbines by differential ballast control. This new concept is based on the idea of pitching the floater with respect to the water surface, thereby achieving a desired tilt of the turbine rotor disk. The pitch attitude is controlled by moving water ballast among the columns of the floater. This study considers the application of differential ballast control to a conceptual 10 MW wind turbine installed on two platforms, differing in size, weight and geometry. The analysis considers: a) the aerodynamic effects caused by rotor tilt on the power capture of the wake-steering turbine and at various downstream distances in its wake; b) the effects of tilting on fatigue and ultimate loads, limitedly to one of the two turbine-platform layouts; and c) for both configurations, the necessary amount of water movement, the time to achieve a desired attitude and the associated energy expenditure. Results indicate that – in accordance with previous research – steering the wake towards the sea surface leads to larger power gains than steering it towards the sky. Limitedly to the structural analysis conducted on one of the turbine-platform configurations, it appears that these gains can be obtained with only minor effects on loads, assuming a cautious application of vertical steering only in benign ambient conditions. Additionally, it is found that rotor tilt can be achieved in the order of minutes for the lighter of the two configurations, with reasonable water ballast movements. Although the analysis is preliminary and limited to the specific cases considered here, results seem to suggest that the concept is not unrealistic, and should be further investigated as a possible means to achieve variable tilt control for vertical wake steering in floating turbines.

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“…In the precursor simulation, the ABL is driven by a pressure gradient adjusted to maintain an horizontally-averaged mean of 8m/s from the west at z=100m (a few meters above hub height z h =89m). In the region spanned by the turbines (z <152m) the streamwise mean velocity is well approximated by the logarithmic law and the vertical wind veer is less than 4 o (see Cossu, 2020b, where the same ABL has been already considered).…”

Section: Problem Formulationmentioning

confidence: 99%

“…3b) leading to a stronger downwash which more efficiently exploits the vertical velocity gradient. Smaller values of the optimal tilt angle ϕ would probably be found if C T was held constant instead of β (as in Cossu, 2020b).…”

mentioning

confidence: 99%

Wake redirection at higher axial induction

Cossu¹

2020

Preprint

Self Cite

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Abstract. The energy produced by wind plants can be increased by mitigating the negative effects of turbine-wakes interactions. In this context, axial induction control and wake redirection, obtained by intentionally yawing or tilting the rotor axis away from the mean wind direction, have been the subject of extensive investigations. We have recently shown that the combination of static tilt control with static axial over-induction results in significant power gains. However, these early results were based on idealized turbine models where wake-rotation effects, radial force distributions and realistic turbine controller effects were neglected. In this study we therefore compute power gains that can be obtained by operating tilted rotors at higher axial induction for the more realistic native NREL 5-MW turbine model implemented in SOWFA. We then extend this approach to the case of yaw control. We show that power gains obtained by standard wake redirection based on yaw or tilt control are highly enhanced when the yawed or tilted turbines are operated at higher axial induction. These results confirm our early findings for the case of tilt control and extend them to the case of yaw control suggesting an high potential for the practical application of overinductive wake redirection.

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Evaluation of tilt control for wind-turbine arrays in the atmospheric boundary layer

Cited by 5 publications

References 54 publications

Wake steering of multirotor wind turbines

Wake steering of multirotor wind turbines

Vertical wake deflection for floating wind turbines by differential ballast control

Wake redirection at higher axial induction

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