Large eddy simulations of the effect of vertical staggering in large wind farms

Zhang, Mengqi; Arendshorst, Mark G.; Stevens, Richard J. A. M.

doi:10.1002/we.2278

Cited by 35 publications

(31 citation statements)

References 58 publications

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“…Finally, future work may benefit from using an improved wake model. A recent study by Zhang et al suggest that wakes close to the ground recover slowly, and as a result, the performance of the shorter turbines in the a multiple‐hub‐height wind farm can be lower than the performance predicted by an engineering wake model. Improving the wake model used to consider this phenomenon may be beneficial.…”

Section: Discussionmentioning

confidence: 99%

Optimization of turbine design in wind farms with multiple hub heights, using exact analytic gradients and structural constraints

2019

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Wind farms are generally designed with turbines of all the same hub height. If wind farms were designed with turbines of different hub heights, wake interference between turbines could be reduced, lowering the cost of energy (COE). This paper demonstrates a method to optimize onshore wind farms with two different hub heights using exact, analytic gradients. Gradient‐based optimization with exact gradients scales well with large problems and is preferable in this application over gradient‐free methods. Our model consisted of the following: a version of the FLOw Redirection and Induction in Steady‐State wake model that accommodated three‐dimensional wakes and calculated annual energy production, a wind farm cost model, and a tower structural model, which provided constraints during optimization. Structural constraints were important to keep tower heights realistic and account for additional mass required from taller towers and higher wind speeds. We optimized several wind farms with tower height, diameter, and shell thickness as coupled design variables. Our results indicate that wind farms with small rotors, low wind shear, and closely spaced turbines can benefit from having two different hub heights. A nine‐by‐nine grid wind farm with 70‐meter rotor diameters and a wind shear exponent of 0.08 realized a 4.9% reduction in COE by using two different tower sizes. If the turbine spacing was reduced to 3 diameters, the reduction in COE decreased further to 11.2%. Allowing for more than two different turbine heights is only slightly more beneficial than two heights and is likely not worth the added complexity.

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Section: Discussionmentioning

confidence: 99%

Optimization of turbine design in wind farms with multiple hub heights, using exact analytic gradients and structural constraints

2019

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“…Some recent numerical studies 29,32,33 have implemented the concept of the vertical staggering in the turbine arrangement to mitigate wake effects and then to improve wind farm performance. Their simulation results reveal that the vertical staggering arrangement can effectively increase the power production of the turbines located in the entry area of the wind farm.…”

Section: Introductionmentioning

confidence: 99%

Effects of inflow turbulence intensity and turbine arrangements on the power generation efficiency of large wind farms

Lin

Chang

2020

Wind Energy

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In this study, we conduct a series of large-eddy simulations (LESs) to study the impact of different incoming turbulent boundary layer flows over large wind farms, with a particular focus on the overall efficiency of electricity production and the evolution of the turbine wake structure. Five representative turbine placements in the large wind farm are considered, including an aligned layout and four staggered layouts with lateral or vertical offset arrangements. Four incoming flow conditions are used and arranged from the LESs of the ABL flow over homogeneous flat surfaces with four different aerodynamic roughness lengths (i.e., z0 = 0.5, 0.1, 0.01, and 0.0001 m), where the hub-height turbulence intensity levels are about 11.1%, 8.9%, 6.8%, and 4.9%, respectively. The simulation results indicate that an enhancement in the inflow turbulence level can effectively increase the power generation efficiency in the large wind farms, with about 23.3% increment on the overall farm power production and up to about 32.0% increment on the downstream turbine power production. Under the same inflow condition, the change of the turbine-array layouts can increase power outputs within the first 10 turbine rows, which has a maximum increment of about 26.5% under the inflow condition with low turbulence. By comparison, the increase of the inflow turbulence intensity facilitates faster wake recovery that raises the power generation efficiency of large wind farms than the adjustment of the turbine placing layouts. K E Y W O R D Slarge eddy simulation, power output, surface roughness, turbulence intensity, wind farm layout

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“…We, however, leave this term in its original form because of (i) its potential use in imaging techniques to simulate ground effects (Crespo, Hernandez & Frandsen 1999) as well as (ii) its potential application in studying wind farms with variable hub heights (i.e. vertical staggering) (Zhang, Arendshorst & Stevens 2019).…”

Section: Derivation Of Wind Farm Analytical Solutionmentioning

confidence: 99%