Analytical modelling of wind speed deficit in large offshore wind farms

Frandsen, Sten Tronæs; Barthelmie, R.J.; Pryor, Sara C.; Rathmann, Ole; Larsen, Søren Ejling; Højstrup, Jørgen; Thøgersen, M.L.

doi:10.1002/we.189

Cited by 724 publications

(550 citation statements)

References 7 publications

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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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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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“…Several studies have argued that the adjustment of the ABL to the increased drag by the wind turbines is comparable to a surface-roughness transition (Crespo et al 1999;Frandsen et al 2006). Elliott (1958) was the first to study the adaptation of the flow close to the ground to a step change in surface roughness.…”

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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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“…The breakdown voltage is illustrated in Figure 12. The breakdown voltage at γ = 25 g/m 3 is lower than the breakdown voltage at γ = 18 g/m 3 by about 80 kV. This means the higher the air humidity, the earlier the UL is generated and the larger the Rp.…”

Section: Long Gap Breakdown Experiments For a Scaled Wind Turbinementioning

confidence: 88%

“…where H L is the altitude, km; γ 0 is the standard absolute humidity at sea level under standard atmospheric condition with a value of 11 g/m 3 . Equations (15)- (17) are incorporated with Equation (14) to obtain the relationship between the electric field intensity of streamer area E str and the altitude, represented as:…”

Section: Relationship Between D Max and Altitudementioning

confidence: 99%

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An Electro-Geometric Model for Lightning Shielding of Multiple Wind Turbines

et al. 2017

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Wind turbine blades being struck by lightning is one of the most urgent problems facing wind farms. In order to reduce the probability of lightning accidents on wind farms, this paper presents a new electro-geometric model for multiple turbines. In this new model, based on the physical model of lightning leader development, the striking distance range of the blade tip receptor is calculated, taking into account the influence of the charged particles around the blade. Lightning shielding amongst multiple turbines is provided in combination with the traditional electro-geometric model, and a criterion formula is obtained for mutual shielding for multiple turbines. The influence of environmental factors, such as temperature, atmospheric pressure, air humidity, and altitude, on lightning shielding on large-scale wind farms is also analyzed by studying the lightning shielding distance between wind turbines. The calculation shows that the larger the relative air density and the absolute humidity, and the lower the altitude, and the larger the lightning shielding distance between wind turbines. The method proposed in this paper provides a theoretical basis for the lightning protection on wind farms under different environmental conditions.

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Analytical modelling of wind speed deficit in large offshore wind farms

Cited by 724 publications

References 7 publications

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

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

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

An Electro-Geometric Model for Lightning Shielding of Multiple Wind Turbines

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