Turbulent flow and scalar transport through and over aligned and staggered wind farms

Markfort, Corey D.; Zhang, Wei; Porté‐Agel, Fernando

doi:10.1080/14685248.2012.709635

Cited by 55 publications

(70 citation statements)

References 53 publications

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“…This leads to a higher level of shear production of turbulence kinetic energy and, in turn, a more evident enhancement of the turbulence levels in the upper half of the wake. These effects have been reported in recent wind-tunnel [6,7,14,17,18], field [19] and numerical simulation [8,20] studies. The thickness of this shear layer increases with downwind distance and it eventually merges at a distance of about two to five rotor diameters from the turbine, corresponding to the end of the near-wake region.…”

Section: Introductionsupporting

confidence: 64%

Atmospheric Turbulence Effects on Wind-Turbine Wakes: An LES Study

2012

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A numerical study of atmospheric turbulence effects on wind-turbine wakes is presented. Large-eddy simulations of neutrally-stratified atmospheric boundary layer flows through stand-alone wind turbines were performed over homogeneous flat surfaces with four different aerodynamic roughness lengths. Emphasis is placed on the structure and characteristics of turbine wakes in the cases where the incident flows to the turbine have the same mean velocity at the hub height but different mean wind shears and turbulence intensity levels. The simulation results show that the different turbulence intensity levels of the incoming flow lead to considerable influence on the spatial distribution of the mean velocity deficit, turbulence intensity, and turbulent shear stress in the wake region. In particular, when the turbulence intensity level of the incoming flow is higher, the turbine-induced wake (velocity deficit) recovers faster, and the locations of the maximum turbulence intensity and turbulent stress are closer to the turbine. A detailed analysis of the turbulence kinetic energy budget in the wakes reveals also an important effect of the incoming flow turbulence level on the magnitude and spatial distribution of the shear production and transport terms.

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Section: Introductionsupporting

confidence: 64%

Atmospheric Turbulence Effects on Wind-Turbine Wakes: An LES Study

2012

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“…In contrast, in the staggered farm, the flow is more uniform in the spanwise direction and no high-speed channels are clearly visible. Similar flow pattern has been shown by Meyer and Meneveau [38], Markfort et al [39] and Wu and Porté-Agel [24]. In addition, in the staggered farms, the turbine wakes have a longer distance to recover before the next downwind turbine, which results in a higher velocity at the turbines and, consequently, larger power output compared with the aligned s7×7-Γ1 a7×7-Γ1 s7×7-Γ10 a7×7-Γ10…”

Section: Layout Effectsupporting

confidence: 54%

The Effect of Free-Atmosphere Stratification on Boundary-Layer Flow and Power Output from Very Large Wind Farms

2013

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Large-eddy simulation is used to study the influence of free-atmosphere stratification on the structure of atmospheric boundary-layer flow inside and above very large wind farms, as well as the power extracted by the wind turbines. In the simulations, tuning-free Lagrangian scale-dependent dynamic models are used to model the subgrid-scale turbulent fluxes, while the turbine-induced forces are parameterized with an actuator-disk model. It is shown that for a given surface cover (with and without turbines) thermal stratification of the free atmosphere reduces the entrainment from the flow above compared with the unstratified case, leading to lower boundary-layer depth. Due to the fact that in very large wind farms vertical energy transport associated with turbulence is the only source of kinetic energy, lower entrainment leads to lower power production by the wind turbines. In particular, for the wind-turbine arrangements considered in the present work, the power output from the wind farms is reduced by about 35% when the potential temperature lapse rate in the free atmosphere increases from 1 to 10 K/km (within the range of values typically observed in the atmosphere). Moreover, it is shown that the presence of the turbines has significant effect on the growth of the boundary layer. Inspired by the obtained results, a simple one-dimensional model is developed to account for the effect of free-atmosphere stability on the mean flow and the power output from very large wind farms.

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“…It is now well understood that when several wind turbines are clustered together forming a wind farm, the net harvested power is less than what theoretically would be extracted by an equal number of isolated turbines (Barthelmie et al 2010). Several works have analyzed the effects of wind-turbine arrangement and wake superposition on the resultant harvested power (Barthelmie et al 2007(Barthelmie et al , 2009; Barthelemie and Jensen 2010;Porté-Agel et al 2013;Stevens et al 2014) as well as wake interactions and the wake-recovery processes (Frandsen 1992;Emeis and Frandsen 1993;Frandsen et al 2006;Cal et al 2010;Markfort et al 2012). Analytical wake models for wind farms developed decades ago (Lissaman 1979;Jensen 1983;Katic et al 1986) continue to serve as the bedrock of various engineering software packages used for wind-farm design such as the Wind Atlas Analysis and Application Program (WAsP).…”

Section: Introductionmentioning

confidence: 99%

Perturbations to the Spatial and Temporal Characteristics of the Diurnally-Varying Atmospheric Boundary Layer Due to an Extensive Wind Farm

Sharma

Parlange

Calaf

2016

Boundary-Layer Meteorol

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The effect of extensive terrestrial wind farms on the spatio-temporal structure of the diurnally-evolving atmospheric boundary layer is explored. High-resolution largeeddy simulations of a realistic diurnal cycle with an embedded wind farm are performed. Simulations are forced by a constant geostrophic velocity with time-varying surface boundary conditions derived from a selected period of the CASES-99 field campaign. Through analysis of the bulk statistics of the flow as a function of height and time, it is shown that extensive wind farms shift the inertial oscillations and the associated nocturnal low-level jet vertically upwards by approximately 200 m; cause a three times stronger stratification between the surface and the rotor-disk region, and as a consequence, delay the formation and growth of the convective boundary layer (CBL) by approximately 2 h. These perturbations are shown to have a direct impact on the potential power output of an extensive wind farm with the displacement of the low-level jet causing lower power output during the night as compared to the day. The low-power regime at night is shown to persist for almost 2 h beyond the morning transition due to the reduced growth of the CBL. It is shown that the wind farm induces a deeper entrainment region with greater entrainment fluxes. Finally, it is found that the diurnally-averaged effective roughness length for wind farms is much lower than the reference value computed theoretically for neutral conditions.

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Turbulent flow and scalar transport through and over aligned and staggered wind farms

Cited by 55 publications

References 53 publications

Atmospheric Turbulence Effects on Wind-Turbine Wakes: An LES Study

Atmospheric Turbulence Effects on Wind-Turbine Wakes: An LES Study

The Effect of Free-Atmosphere Stratification on Boundary-Layer Flow and Power Output from Very Large Wind Farms

Perturbations to the Spatial and Temporal Characteristics of the Diurnally-Varying Atmospheric Boundary Layer Due to an Extensive Wind Farm

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