The impact of turbulence intensity and atmospheric stability on power deficits due to wind turbine wakes at Horns Rev wind farm

Hansen, Kurt Schaldemose; Barthelmie, R.J.; Jensen, Lotte; Sommer, Anders

doi:10.1002/we.512

Cited by 406 publications

(317 citation statements)

References 12 publications

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“…In the simulations, Vestas V80-2MW wind turbines, with a rotor diameter (D) of 80m and a hub-height (z h ) of 70m, are immersed in the flow. Based on the operational records of Vestas V80−2MW wind turbines reported by Hansen et al 36 , the turbines reach a mean angular velocity of 16.1 rpm when the incoming (upwind) mean wind speed at hub height is U hub ≈ 8 ms −1 . The code is run for a long-enough time to guarantee that quasi-steady conditions are reached.…”

Section: Numerical Setupmentioning

confidence: 99%

Influence of atmospheric stability on wind-turbine wakes: A large-eddy simulation study

2015

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In this study, large-eddy simulation is combined with a turbine model to investigate the influence of atmospheric thermal stability on wind-turbine wakes. The simulation results show that atmospheric stability has a significant effect on the spatial distribution of the mean velocity deficit and turbulence statistics in the wake region as well as the wake meandering characteristics downwind of the turbine. In particular, the enhanced turbulence level associated with positive buoyancy under the convective condition leads to a relatively larger flow entrainment and, thus, a faster wake recovery. For the particular cases considered in this study, the growth rate of the wake is about 2.4 times larger for the convective case than for the stable one. Consistent with this result, for a given distance downwind of the turbine, wake meandering is also stronger under the convective condition compared with the neutral and stable cases. It is also shown that, for all the stability cases, the growth rate of the wake and wake meandering in the vertical direction are smaller compared with the ones in the lateral direction. This is mainly related to the different turbulence levels of the incoming wind in the different directions, together with the anisotropy imposed by the presence of the ground. It is also found that the wake velocity deficit is well characterized by a modified version of a recently proposed analytical model that is based on mass and momentum conservation and the assumption of a self-similar Gaussian distribution of the velocity deficit. Specifically, using a two-dimensional elliptical (instead of axisymmetric) Gaussian distribution allows to account for the different lateral and vertical growth rates, particularly in the convective case where the non-axisymmetry of the wake is stronger. Detailed analysis of the resolved turbulent kinetic energy budget in the wake reveals also that thermal stratification considerably affects the magnitude and spatial distribution of the turbulence production, dissipation and transport terms.

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Section: Numerical Setupmentioning

confidence: 99%

Influence of atmospheric stability on wind-turbine wakes: A large-eddy simulation study

2015

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“…While summer nocturnal lowlevel jets increase boundary-layer wind speeds (Vanderwende et al 2015;Bonin et al 2015), providing ample wind resources during the summer in the Great Plains, the power deficit, the reduction in power production of downwind turbines located within the wakes, increases with atmospheric stability (Hansen et al 2012). New approaches to yawing upwind turbines in order to improve the power production of downwind turbines (Fleming et al 2015(Fleming et al , 2016 require accurate wake prediction.…”

Section: The Evening Boundary Layer and Turbine Wakesmentioning

confidence: 99%

Observing and Simulating Wind-Turbine Wakes During the Evening Transition

Lee

Lundquist

2017

Boundary-Layer Meteorol

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Wind-turbine-wake evolution during the evening transition introduces variability to wind-farm power production at a time of day typically characterized by high electricity demand. During the evening transition, the atmosphere evolves from an unstable to a stable regime, and vertical stratification of the wind profile develops as the residual planetary boundary layer decouples from the surface layer. The evolution of wind-turbine wakes during the evening transition is examined from two perspectives: wake observations from single turbines, and simulations of multiple turbine wakes using the mesoscale Weather Research and Forecasting (WRF) model. Throughout the evening transition, the wake's wind-speed deficit and turbulence enhancement are confined within the rotor layer when the atmospheric stability changes from unstable to stable. The height variations of maximum upwind-downwind differences of wind speed and turbulence intensity gradually decrease during the evening transition. After verifying the WRF-model-simulated upwind wind speed, wind direction and turbulent kinetic energy profiles with observations, the wind-farm-scale wake evolution during the evening transition is investigated using the WRF-model wind-farm parametrization scheme. As the evening progresses, due to the presence of the wind farm, the modelled hub-height wind-speed deficit monotonically increases, the relative turbulence enhancement at hub height grows by 50%, and the downwind surface sensible heat flux increases, reducing surface cooling. Overall, the intensifying wakes from upwind turbines respond to the evolving atmospheric boundary layer during the evening transition, and undermine the power production of downwind turbines in the evening.

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“…Hansen et al (2012) and Schepers et al (2012) report significantly larger power deficits between the first and second row of turbines while the remaining downstream power deficits were less. We saw a similar effect in the North…”

mentioning

confidence: 93%

“…At an offshore Danish wind farm, Hansen et al (2012) found a strong negative correlation between power deficit and ambient turbulence intensity (i.e., atmospheric stability). Under convective conditions, when turbulence levels were relatively high, smallest power deficits were observed.…”

mentioning

confidence: 93%

“…After careful study of our wind farm layout and the wind rose, we decided to use a ±15 degree wind direction criterion (245 ± 15 degrees at the North and 270 ± 15 degrees at the South Cluster). This eliminated the problem of high scatter as found in Hansen et al (2012) who averaged over small sample sizes. It also seemed appropriate to have a larger wind sector at our site for "likely" wake events since the turbines are not uniformly distributed across a grid.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Synergistic Effects of Turbine Wakes and Atmospheric Stability on Power Production at an Onshore Wind Farm

Wharton¹,

Lundquist²,

Marjanovic³

2012

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The impact of turbulence intensity and atmospheric stability on power deficits due to wind turbine wakes at Horns Rev wind farm

Cited by 406 publications

References 12 publications

Influence of atmospheric stability on wind-turbine wakes: A large-eddy simulation study

Influence of atmospheric stability on wind-turbine wakes: A large-eddy simulation study

Observing and Simulating Wind-Turbine Wakes During the Evening Transition

Synergistic Effects of Turbine Wakes and Atmospheric Stability on Power Production at an Onshore Wind Farm

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