Extending the applicability of a wind-farm gravity-wave model to vertically non-uniform atmospheres

Devesse, Koen; Lanzilao, Luca; Jamaer, Sebastiaan; Lipzig, Nicole Van; Meyers, Johan

doi:10.5194/wes-2021-138

Cited by 5 publications

(18 citation statements)

References 21 publications

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“…Therefore, we are planning to increase the domain lateral dimension at the expense of a higher computational cost. Furthermore, it has been observed that accounting for a height-dependent Brunt-Väisälä frequency and wind speed in the free atmosphere could impact the wind-farm performances [40]. Therefore, it would be interesting to relax the assumptions of constant free lapse rate and zero shear in the free atmosphere and see how results would change.…”

Section: Discussionmentioning

confidence: 99%

Effects of self-induced gravity waves on finite wind-farm operations using a large-eddy simulation framework

Lanzilao

Meyers

2022

J. Phys.: Conf. Ser.

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In the present study, we use large-eddy simulation (LES) to investigate how a capping inversion in combination with a stable free atmosphere influences the flow development and energy extraction in a large finite wind farm with a staggered and aligned layout. In the conventionally neutral boundary layer (CNBL), we find that gravity waves induce an unfavourable pressure gradient in the induction region of the farm which contributes to the upstream blockage, decreasing the available energy for first-row turbines. However, a favourable pressure gradient establishes through the farm in such conditions, which redistributes the energy and enhances wake recovery. These results are compared with a farm operating in the neutral boundary layer (NBL). Here, we find that only hydrodynamic effects induced by the turbines drag play a role, which cause minor pressure perturbations across the domain. For the selected atmospheric conditions, the power losses generated by the upstream blockage are balanced by the enhanced wake recovery promoted by the favourable pressure gradient throughout the farm. Consequently, the staggered farm efficiency in the CNBL is 8.8% higher than in the NBL. We note that this difference in efficiency is slightly enhanced by the 0.5? difference in wind direction at the location of the first-row turbines between the CNBL and NBL cases, which is caused by the presence of flow blockage. Since both simulations are forced with an equal turbulent velocity profile, the variation in performance is solely caused by the different vertical temperature profiles in the main domain. Finally, the staggered layout leads to a slightly stronger flow blockage than the aligned one when both farms operate in the CNBL.

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Section: Discussionmentioning

confidence: 99%

Effects of self-induced gravity waves on finite wind-farm operations using a large-eddy simulation framework

Lanzilao

Meyers

2022

J. Phys.: Conf. Ser.

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“…Examples of these models can be found in Smith (2010), Allaerts & Meyers (2018), Allaerts & Meyers (2019), Devesse et al. (2022) and Smith (2022, 2023). In the current section, we perform a comparison of our results against some of the simplest wind-farm gravity-wave linear-theory models.…”

Section: Sensitivity Of Wind-farm Performance To the Atmospheric Statementioning

confidence: 99%

“…2018; Lanzilao & Meyers 2022, 2023 b ; Maas 2022, 2023; Maas & Raasch 2022) and much faster linearized wind-farm flow models (Allaerts & Meyers 2019; Devesse et al. 2022; Smith 2022, 2023).…”

Section: Introductionmentioning

confidence: 99%

A parametric large-eddy simulation study of wind-farm blockage and gravity waves in conventionally neutral boundary layers

Lanzilao,

Meyers

2024

J. Fluid Mech.

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We present a suite of large-eddy simulations (LES) of a wind farm operating in conventionally neutral boundary layers. A fixed 1.6 GW wind farm is considered for 40 different atmospheric stratification conditions to investigate effects on wind-farm efficiency and blockage, as well as related gravity-wave excitation. A tuned Rayleigh damping layer and a wave-free fringe-region method are used to avoid spurious excitation of gravity waves, and a domain-size study is included to evaluate and minimize effects of artificial domain blockage. A fully neutral reference case is also considered, to distinguish between a case with hydrodynamic blockage only, and cases that include hydrostatic blockage induced by the air column above the boundary layer and the excitation of gravity waves therein. We discuss in detail the dependence of gravity-wave excitation, flow fields and wind-farm blockage on capping-inversion height, strength and free-atmosphere lapse rate. In all cases, an unfavourable pressure gradient is present in front of the farm, and a favourable pressure gradient in the farm, with hydrostatic contributions arising from gravity waves at least an order of magnitude larger than hydrodynamic effects. Using respectively non-local and wake efficiencies $\eta _{nl}$ and $\eta _{w}$ , we observe a strong negative correlation between the unfavourable upstream pressure rise and $\eta _{nl}$ , and a strong positive correlation between the favourable pressure drop in the farm and $\eta _{w}$ . Using a simplified linear gravity-wave model, we formulate a simple scaling for the ratio $(1-\eta _{nl})/\eta _{w}$ , which matches reasonably well with the LES results.

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“…As a consequence, the APM needs to be coupled with an engineering wake model in order to capture turbine-turbine interactions. To achieve this, three different approaches have been developed so far, namely the IOP Publishing doi:10.1088/1742-6596/2767/9/092079 2 Upstream (US) coupling method originally developed by Allaerts and Meyers [4], the Velocity Matching (VM) technique [5], and the Pressure-Based (PB) velocity reconstruction [6]. All three coupling methods have been implemented in a new open-source code, called WAYVE (Wind-fArm gravitY-waVe and blockagE), which will be used in this paper [7].…”

Section: Introductionmentioning

confidence: 99%

Comparing methods for coupling wake models to an atmospheric perturbation model in WAYVE

Devesse,

Stipa,

Brinkerhoff

et al. 2024

J. Phys.: Conf. Ser.

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As offshore wind farms grow in size, the blockage effect associated with the atmospheric gravity waves they trigger is expected to become more important. To model this, recent research has produced an Atmospheric Perturbation Model (APM), which simulates the mesoscale flow in the atmospheric boundary layer at a low computational cost compared to traditional methods. However, as a simplified reduced-order model, it can not resolve individual turbine wakes, and has to be coupled to an engineering wake model to predict farm power output. Over the years, three coupling methods have been developed, and been combined into the open-source framework WAYVE. This paper compares them, discussing both their theoretical validity and their performance. For the latter, we validate the velocities and power outputs predicted by WAYVE against 27 LES simulations. We find that the velocity matching (VM) and the pressure-based (PB) methods perform the best. Of these two, the VM method is more consistent with the APM output, while the PB method has a significantly lower computational cost.

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Extending the applicability of a wind-farm gravity-wave model to vertically non-uniform atmospheres

Cited by 5 publications

References 21 publications

Effects of self-induced gravity waves on finite wind-farm operations using a large-eddy simulation framework

Effects of self-induced gravity waves on finite wind-farm operations using a large-eddy simulation framework

A parametric large-eddy simulation study of wind-farm blockage and gravity waves in conventionally neutral boundary layers

Comparing methods for coupling wake models to an atmospheric perturbation model in WAYVE

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