The flow upstream of a row of aligned wind turbine rotors and its effect on power production

Forsting, Alexander Meyer; Troldborg, Niels; Gaunaa, Mac

doi:10.1002/we.1991

Cited by 49 publications

(69 citation statements)

References 13 publications

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“…In McTavish [17], wind tunnel measurements of three scaled-down turbines revealed production increases of a similar magnitude when the hub-to-hub distance was narrowed to 1.5 D. A flow model of the configuration yielded a similar result. Finally, Forsting [18] presented results from RANS simulations indicating that five turbines in a row perpendicular to the flow will outproduce the turbines in isolation by approximately 0.5% when the hub-to-hub spacing is 3.0 D. Unlike the RANS model, a vortex model predicted turbines in this configuration to have a negligible influence on each other for perpendicular flow. For non-perpendicular wind directions, however, both models predicted significant production variation along the row.…”

Section: Introductionmentioning

confidence: 99%

Wind Farm Blockage and the Consequences of Neglecting Its Impact on Energy Production

Bleeg

Purcell²,

Ruisi³

et al. 2018

Energies

143

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Measurements taken before and after the commissioning of three wind farms reveal that the wind speeds just upstream of each wind farm decrease relative to locations farther away after the turbines are turned on. At a distance of two rotor diameters upstream, the average derived relative slowdown is 3.4%; at seven to ten rotor diameters upstream, the average slowdown is 1.9%. Reynolds-Averaged Navier-Stokes (RANS) simulations point to wind-farm-scale blockage as the primary cause of these slowdowns. Blockage effects also cause front row turbines to produce less energy than they each would operating in isolation. Wind energy prediction procedures in use today ignore this effect, resulting in an overprediction bias that pervades the entire wind farm.

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Section: Introductionmentioning

confidence: 99%

Wind Farm Blockage and the Consequences of Neglecting Its Impact on Energy Production

Bleeg

Purcell²,

Ruisi³

et al. 2018

Energies

143

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show abstract

“…This effect is referred to as “wind farm blockage,” and the area that is affected is called the induction zone. Wind farm developers and owners have turned their attention to this phenomenon because the current wind energy prediction procedures neglect wind farm blockage effects, resulting in an overprediction of the wind farm production (see, e.g., Meyer Forsting et al 1 ), and biases in power curve measurements. This work presents a novel methodology to assess wind farm production that accounts for wakes and blockage effects.…”

Section: Introductionmentioning

confidence: 99%

“…Measurements using lidar technologies on full‐scale wind farms can be found in the work of Asimakopoulos et al 19 or Simley et al 20 Field and wind tunnel measurements were also used by Howard and Guala and compared with previous models. 21 Computational fluid dynamics (CFD) methods, such as Reynolds‐averaged Navier–Stokes (RANS) simulations, have also been used to assess the wind farm blockage effect 1,22,23 . Meyer Forsting et al 24 include a comparison of the induction zone velocity with lidar measurements.…”

Section: Introductionmentioning

confidence: 99%

Assessing the blockage effect of wind turbines and wind farms using an analytical vortex model

Branlard

Forsting

2020

Wind Energy

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Wind farm blockage effects are currently neglected in the prediction of wind farm energy yield, typically leading to an overestimation of the production. This work presents a novel method to assess wind farm production, while accounting for blockage effects. We apply a vortex model, based on a cylindrical wake, to assess induction effects. We present variations of the model to account for finite wake length, finite tip-speed ratios, and the proximity to the ground. The results are applied to single rotors in aligned and yawed conditions and to different wind farm layouts. We provide far-field approximations for faster estimates of the velocity field. Further, this article includes a new methodology to couple the induction model to engineering wake models, such as the ones present in the FLOw Redirection and Induction in Steady State (FLORIS). We compare the results to actuator disk simulations for various operating conditions of a single turbine and different wind farm layouts. We found that the mean relative error of the model in the induction zone is typically around 0.2% compared with actuator disk simulations. The computational time of the velocity field using the analytical vortex model is three orders of magnitude less than the one obtained with the actuator disk simulation.

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“…The presence of a wind farm implies a number of modifications to the approaching flow. Upstream of the first turbine row, a blockage effect can be observed as a global velocity reduction compared with the undisturbed flow . A numerical quantification of this effect is currently only possible by performing time‐consuming CFD simulations, which are not feasible for industrial purposes.…”

Section: Introductionmentioning

confidence: 99%

“…Upstream of the first turbine row, a blockage effect can be observed as a global velocity reduction compared with the undisturbed flow. 14 A numerical quantification of this effect is currently only possible by performing time-consuming CFD simulations, which are not feasible for industrial purposes. However, faster state-of-the-art engineering wake models are not able to account for this upstream flow region at all.…”

Section: Introductionmentioning

confidence: 99%

A linearized numerical model of wind-farm flows

et al. 2016

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A fast and reasonably accurate numerical three‐dimensional wake model able to predict the flow behaviour of a wind farm over a flat terrain has been developed. The model is based on the boundary‐layer approximation of the Navier–Stokes equations, linearized around the incoming atmospheric boundary layer, with the assumption that the wind turbines provide a small perturbation to the velocity field. The linearization of the actuator‐disc theory brought additional insights that could be used to understand the behaviour, as well as the limitations, of a flow model based on linear methods: for instance, it is shown that an adjustment of the turbine's thrust coefficient is necessary in order to obtain the same wake velocity field provided by the actuator disc theory within the used linear framework. The model is here validated against two independent wind‐tunnel campaigns with a small and a large wind farm aimed at the characterization of the flow above and upstream of the farms, respectively. The developed model is, in contrary to current engineering wake models, able to account for effects occurring in the upstream flow region, thereby including more physical mechanisms than other simplified approaches. The conducted simulations (in agreement with the measurement results) show that the presence of a wind farm affects the approaching flow far more upstream than generally expected and definitely beyond the current industrial standards. Despite the model assumptions, several velocity statistics above wind farms have been properly estimated providing an insight into the transfer of momentum inside the turbine rows. Copyright © 2016 John Wiley & Sons, Ltd.

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The flow upstream of a row of aligned wind turbine rotors and its effect on power production

Cited by 49 publications

References 13 publications

Wind Farm Blockage and the Consequences of Neglecting Its Impact on Energy Production

Wind Farm Blockage and the Consequences of Neglecting Its Impact on Energy Production

Assessing the blockage effect of wind turbines and wind farms using an analytical vortex model

A linearized numerical model of wind-farm flows

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