Numerical modelling for wind farm operational assessment in complex terrain

Castellani, Francesco; Astolfi, Davide; Burlando, Massimiliano; Terzi, Ludovico

doi:10.1016/j.jweia.2015.07.016

Cited by 48 publications

(22 citation statements)

References 18 publications

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“…Downstream of the hill crest, the perturbations caused by the topology may act both in favour or disadvantage for the turbines, depending on how the wind‐turbine wakes are deflected by the site‐specific terrain features, and whether the flow separates. In some complex‐terrain situations, turbines placed at downwind hill slopes can perform better because of the vertical shift introduced between the rotors, while the opposite has been noted for turbines placed on upwind slopes . The actual flow at a site with large terrain variations is ultimately unique and might not only depend on the local topographical situation, but also on terrain features upstream of the investigated wind site .…”

Section: Introductionmentioning

confidence: 99%

“…In some complex-terrain situations, turbines placed at downwind hill slopes can perform better because of the vertical shift introduced between the rotors, while the opposite has been noted for turbines placed on upwind slopes. [20][21][22][23] The actual flow at a site with large terrain variations is ultimately unique and might not only depend on the local topographical situation, but also on terrain features upstream of the investigated wind site. 24,25 The evolving climate conditions and the diurnal cycle of the atmospheric boundary layer will introduce additional variations in the flow, which will be seen in the data obtained from field measurements, 26,27 but the uniqueness of the prevailing flow inhibits comparisons between data measured at different complex-terrain sites.…”

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confidence: 99%

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A wind‐tunnel study of the wake development behind wind turbines over sinusoidal hills

2018

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In the present work, the wake development behind small‐scale wind turbines is studied when introducing local topography variations consisting of a series of sinusoidal hills. Additionally, wind‐tunnel tests with homogeneous and sheared turbulent inflows were performed to understand how shear and ambient turbulence influence the results. The scale of the wind‐turbine models was about 1000 times smaller than full‐size turbines, suggesting that the present results should only be qualitatively extrapolated to real‐field scenarios. Wind‐tunnel measurements were made by means of stereoscopic particle image velocimetry to characterize the flow velocity in planes perpendicular to the flow direction. Over flat terrain, the wind‐turbine wake was seen to slowly approach the ground while it propagated downstream. When introducing hilly terrain, the downward wake deflection was enhanced in response to flow variations induced by the hills, and the turbulent kinetic energy content in the wake increased because of the speed‐up seen over the hills. The combined wake observed behind 2 streamwise aligned turbines was more diffused and when introducing hills, it was more prone to deflect towards the ground compared to the wake behind an isolated turbine. Since wake interactions are common at sites with multiple turbines, this suggested that it is important to consider the local hill‐induced velocity variations when onshore wind farms are analysed. Differences in the flow fields were seen when introducing either homogeneous or sheared turbulent inflow conditions, emphasizing the importance of accounting for the prevailing turbulence conditions at a given wind‐farm site to accurately capture the downstream wake development.

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

A wind‐tunnel study of the wake development behind wind turbines over sinusoidal hills

2018

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“…The selected testing ground was a subcluster of four turbines from a wind farm sited in Italy in a very complex terrain. Preliminary studies 16,25 showed that, when the wind blows from the west, the wake of the upstream turbine is more mitigated than what one would expect in flat terrain. This phenomenon is so relevant that the most downstream turbine is the best performing of the cluster.…”

Section: Conclusion and Further Directionsmentioning

confidence: 99%

“…See, for example, the interesting developments in Moreno et al 11 and Lee et al, 12 in Peralta et al 13 about the test cases of Askervein Hill 2, 3 and Bolund Hill. 14,15 In particular in Castellani et al, 16 an analysis is proposed of the same test case as in this work. The idea is inquiring to what extent free flow models are capable of capturing what is going on inside the wind farm.…”

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Investigation of terrain and wake effects on the performance of wind farms in complex terrain using numerical and experimental data

et al. 2017

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In this work, the combination effects on wind turbine performances of wakes and terrain‐driven flow are investigated. The test case is a subcluster of four turbines from a wind farm sited in southern Italy in a very complex terrain. The layout, the inter‐turbine distance and the wind rose result in a challenging performance scenery. The subcluster is analyzed, when the wind blows from the west, through computational fluid dynamics numerical simulations and experimental supervisory control and data acquisition data mining. Two wind intensity regimes and several simulation setups are employed. It is shown that the main effect of the terrain is the northward distortion of the wake of the upstream turbine. This explains the non‐trivial yawing patterns of the cluster and the fact that the wake line affects the overall performances of the subcluster less than it would do in flat terrain. It is further shown that the presence of the rest of the subcluster in operation southward deviates the wake line of the upstream turbine. The dependency on wind intensity of these directional distortions allows to estimate the relative importance of wakes and terrain‐driven flow. A bijective feedback between models and data is established and a convincing framework is constructed, for separating and assessing the effect of the terrain and of the single and multiple wake. Copyright © 2017 John Wiley & Sons, Ltd.

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“…In particular, the test case 2 is challenging because, after the upgrade, the nacelle wind speed measurements are not reliable and therefore can't be used as inputs to the model. Further, the site is very complex [10,25] and it is difficult, although necessary, to use the nearby wind turbines as references for the environmental conditions. Despite the different complexity, 1 www.renvicoenergy.com the criticality of test cases 1 and 2 is the same: modeling as precisely as possible the pre-upgrade power output of the upgraded wind turbines.…”

Section: Introductionmentioning

confidence: 99%

Wind Turbine Power Curve Upgrades

Astolfi¹,

Castellani²,

Terzi³

2018

Preprint

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Full-scale wind turbine technology has been widely developing in the recent years and condition monitoring techniques assist at the scope of making 100% technical availability a realistic perspective. In this context, several retrofitting techniques are being used for further improving the efficiency of wind kinetic energy conversion. This kind of interventions is costly and, furthermore, the estimation of the energy enhancement is commonly provided under the hypothesis of ideal conditions, as for example absence of wakes between nearby turbines. A precise quantification of the energy gained by retrofitting is therefore precious in real conditions, that can be very different from ideal ones. In this work, three kinds of retrofitting are studied through the operational data of test case wind farms: improved start-up through pitch angle adjustment near the cut-in, aerodynamic blade retrofitting by means of vortex generators and passive flow control devices, extension of the power curve by raising cut-out and high wind speed cut-in. SCADA data are employed and reliable methods are formulated for estimating the energy improvement from each of the above retrofitting. Further, an insight is provided about wind turbine functioning under very stressing regimes, as for example high wind speeds.retrofitting; further, for some reason as in one of the test cases of the present work, it might happen that the approach can't be employed at all. One might therefore possibly invoke other kinds of precision modeling of wind turbines power curve. It actually is a very fertile field in the scientific literature [14][15][16][17]: as regards these models, the main drawback for their application to the study of wind turbine upgrades is that they are too complex and not enough flexible to be applied to the range of different criticality that the study of wind turbine upgrades poses.The above shortcomings are both circumvented in the present study: this work actually is a collaboration between academia and industry. The industry is Renvico srl 1 , owning and managing 335 MW of full-scale wind turbines in Italy and France. Some wind turbines owned by Renvico have been retrofitted in several ways: this has been a pilot test and the decision of extending the retrofitting to the other wind turbines in the corresponding wind farms has been based on the assessment, coming from this study, of the real profit on the pilot test cases. The SCADA data from the retrofitted and non-retrofitted wind turbines from the wind farms of interest have therefore been shared with the University of Perugia. This academia-industry collaboration, as shall be shown in the next Sections, has produced methods for the study of power curve upgrades, standing at the frontier of the scientific debate and being as well integrable in the everyday industrial management of the wind turbines. This kind of studies on this subject, basing on operational data, has been very recently developing in the scientific literature: in [18], a kernel plus method is adopted for computing ...

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Numerical modelling for wind farm operational assessment in complex terrain

Cited by 48 publications

References 18 publications

A wind‐tunnel study of the wake development behind wind turbines over sinusoidal hills

A wind‐tunnel study of the wake development behind wind turbines over sinusoidal hills

Investigation of terrain and wake effects on the performance of wind farms in complex terrain using numerical and experimental data

Wind Turbine Power Curve Upgrades

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