Wake effects of large offshore wind farms identified from satellite SAR

Christiansen, Merete Bruun; Hasager, Charlotte Bay

doi:10.1016/j.rse.2005.07.009

Cited by 217 publications

(166 citation statements)

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“…It has previously been documented that coastal wind speed gradients are found near Horns Rev using satellite synthetic aperture radar (SAR) wind maps and modeling [13]. Also in [14] and [15] satellite and airborne SAR wind observations showed wind speed gradients locally in and near the Horns Rev 1 wind farm.…”

Section: Discussionmentioning

confidence: 98%

Wind Farm Wake: The Horns Rev Photo Case

et al. 2013

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Abstract:The aim of the paper is to examine the nowadays well-known wind farm wake photographs taken on 12 February 2008 at the offshore Horns Rev 1 wind farm. The meteorological conditions are described from observations from several satellite sensors quantifying clouds, surface wind vectors and sea surface temperature as well as ground-based information at and near the wind farm, including Supervisory Control and Data Acquisition (SCADA) data. The SCADA data reveal that the case of fog formation occurred 12 February 2008 on the 10:10 UTC. The fog formation is due to very special atmospheric conditions where a layer of cold humid air above a warmer sea surface re-condensates to fog in the wake of the turbines. The process is fed by warm humid air up-drafted from below in the counter-rotating swirl generated by the clock-wise rotating rotors. The condensation appears to take place primarily in the wake regions with relatively high axial velocities and high turbulent kinetic energy. The wind speed is near cut-in and most turbines produce very little power. The rotational pattern of spiraling bands produces the large-scale structure of the wake fog.

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Section: Discussionmentioning

confidence: 98%

Wind Farm Wake: The Horns Rev Photo Case

et al. 2013

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“…Full rotor simulations of wind farms are not common due to the size of the domain that must be considered resulting in an impractical computational cost for little benefit. Actuator-disc/line or analytical methods are more common as are wind tunnel experiments with the choice of method depending on application (Christiansen & Hasager 2005, Frandsen et al 2006. For systems larger than two turbines, analytical models are often used, and while these are adequate for optimising a wind farm layout for power output, they cannot give insight into how the flow structure is affected as each turbine interacts with the combined wakes of the upstream turbines.…”

Section: Wake Structure and Propagationmentioning

confidence: 99%

A discussion of wind turbine interaction and stall contributions to wind farm noise

Laratro

Arjomandi

Kelso

et al. 2014

Journal of Wind Engineering and Industrial Aerodynamics

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Elsevier's Policy: An author may use the preprint for personal use, internal institutional use and for permitted scholarly posting. ... Elsevier's AAM Policy: Authors retain the right to use the accepted author manuscript for personal use, internal institutional use and for permitted scholarly posting provided that these are not for purposes of commercial use or systematic distribution. Elsevier believes that individual authors should be able to distribute their AAMs for their personal voluntary needs and interests, e.g. posting to their websites or their institution's repository, e-mailing to colleagues. However, our policies differ regarding the systematic aggregation or distribution of AAMs to ensure the sustainability of the journals to which AAMs are submitted. Therefore, deposit in, or posting to, subject-oriented or centralized repositories (such as PubMed Central), or institutional repositories with systematic posting mandates is permitted only under specific agreements between Elsevier and the repository, agency or institution, and only consistent with the publisher's policies concerning such repositories. Voluntary posting of AAMs in the arXiv subject repository is permitted. ... Highlights-Rotor-wake interaction plays a role in wind farm noise -More wake data needs to be collected -Dynamic stall noise needs to be characterised AbstractWind farms have recently been reported to produce a noise signature that is described as possessing a "thumping" quality. Measurements of these signatures are limited and their effects are debated but their effect on public opinion and complaints make them a concern for researchers in this field. Proposed reasons for these noise signatures include amplitude modulation, interference patterns and wake-rotor interaction. This paper discusses these effects and concludes that wake-rotor interaction plays a role by causing variations in turbulent-inflow noise and dynamic stall. The current state of research into stall noise and wind turbine wake structure is also reviewed and it is concluded that the available information and collected data on wind turbine wake are insufficient to determine how strong this role is. More information on the velocity and turbulence fields in the wake of horizontal-axis wind turbines as well as a characterisation of the noise produced by an airfoil experiencing dynamic stall is required in order to make a full assessment of rotor-wake contributions to wind farm noise.2

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“…In addition to reduced velocities and enhanced turbulence in the turbine region, large wind farms also induce effects on a regional scale beyond their own boundaries, such as wind farm wakes (Christiansen & Hasager 2005;Fitch et al 2012) and internal boundary layers (Chamorro & Porté-Agel 2011;Newman et al 2013). As an increasing amount of wind power capacity is being installed each year (GWEC 2015), insight into the complex wind farm-ABL system and its non-local effects forms a key instrument in improving state-of-the-art wind farm operation and design.…”

Section: Introductionmentioning

confidence: 99%

Boundary-layer development and gravity waves in conventionally neutral wind farms

2017

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While neutral atmospheric boundary layers are rare over land, they occur frequently over sea. In these cases they are almost always of the conventionally neutral type, in which the neutral boundary layer is capped by a strong inversion layer and a stably stratified atmosphere aloft. In the current study, we use large-eddy simulations (LES) to investigate the interaction between a large wind farm that has a fetch of 15 km and a conventionally neutral boundary layer (CNBL) in typical offshore conditions. At the domain inlet, we consider three different equilibrium CNBLs with heights of approximately 300 m, 500 m and 1000 m that are generated in a separate precursor LES. We find that the height of the inflow boundary layer has a significant impact on the wind farm flow development. First of all, above the farm, an internal boundary layer develops that interacts downwind with the capping inversion for the two lowest CNBL cases. Secondly, the upward displacement of the boundary layer by flow deceleration in the wind farm excites gravity waves in the inversion layer and the free atmosphere above. For the lower CNBL cases, these waves induce significant pressure gradients in the farm (both favourable and unfavourable depending on location and case). A detailed energy budget analysis in the turbine region shows that energy extracted by the wind turbines comes both from flow deceleration and from vertical turbulent entrainment. Though turbulent transport dominates near the end of the farm, flow deceleration remains significant, i.e. up to 35 % of the turbulent flux for the lowest CNBL case. In fact, while the turbulent fluxes are fully developed after eight turbine rows, the mean flow does not reach a stationary regime. A further energy budget analysis over the rest of the CNBL reveals that all energy available at turbine level comes from upwind kinetic energy in the boundary layer. In the lower CNBL cases, the pressure field induced by gravity waves plays an important role in redistributing this energy throughout the farm. Overall, in all cases entrainment at the capping inversion is negligible, and also the work done by the mean background pressure gradient, arising from the geostrophic balance in the free atmosphere, is small.

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Wake effects of large offshore wind farms identified from satellite SAR

Cited by 217 publications

References 24 publications

Wind Farm Wake: The Horns Rev Photo Case

Wind Farm Wake: The Horns Rev Photo Case

A discussion of wind turbine interaction and stall contributions to wind farm noise

Boundary-layer development and gravity waves in conventionally neutral wind farms

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