AVATAR: AdVanced Aerodynamic Tools of  lArge Rotors

Schepers, J.C.; Ceyhan, O.; Savenije, Feike; Stettner, M.; Kooijman, H.J.; Chaviarapoulos, P.; Sieros, Giorgos; Ferreira, Carlos; Sørensen, Niels N.; Wächter, Matthias; Stoevesandt, Bernhard; Lutz, Thorsten; González, Ana Marta; Barakos, George N.; Voutsinas, Artemios; Croce, Alessandro; Madsen, Jesper

doi:10.2514/6.2015-0497

Cited by 15 publications

(9 citation statements)

References 12 publications

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“…For consistency, we used the Vestas V80 turbine for all of the square-shaped hypothetical wind farms, although modern offshore wind farms are often equipped with larger and more energy producing turbines (EWEA 2016) and have optimised layouts. In the future it will be interesting to investigate how the wind farm efficiency in different regions behaves for larger wind turbines and for new turbine technologies, such as low induction turbines (Schepers et al 2015).…”

Section: Discussionmentioning

confidence: 99%

Prospects for generating electricity by large onshore and offshore wind farms

Volker

Hahmann

Badger

et al. 2017

Environ. Res. Lett.

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The decarbonisation of energy sources requires additional investments in renewable technologies, including the installation of onshore and offshore wind farms. For wind energy to remain competitive, wind farms must continue to provide low-cost power even when covering larger areas. Inside very large wind farms, winds can decrease considerably from their free-stream values to a point where an equilibrium wind speed is reached. The magnitude of this equilibrium wind speed is primarily dependent on the balance between turbine drag force and the downward momentum influx from above the wind farm. We have simulated for neutral atmospheric conditions, the wind speed field inside different wind farms that range from small (25 km 2 ) to very large (10 5 km 2 ) in three regions with distinct wind speed and roughness conditions. Our results show that the power density of very large wind farms depends on the local free-stream wind speed, the surface characteristics, and the turbine density. In onshore regions with moderate winds the power density of very large wind farms reaches 1 W m −2 , whereas in offshore regions with very strong winds it exceeds 3 W m −2 . Despite a relatively low power density, onshore regions with moderate winds offer potential locations for very large wind farms. In offshore regions, clusters of smaller wind farms are generally preferable; under very strong winds also very large offshore wind farms become efficient.

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Section: Discussionmentioning

confidence: 99%

Prospects for generating electricity by large onshore and offshore wind farms

Volker

Hahmann

Badger

et al. 2017

Environ. Res. Lett.

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“…Technology development has focused on cost reductions based on technological innovations, operation and maintenance optimization, mass production, and grid integration . Commercial wind turbines with 6 to 7 MW rated capacity are available that have 156‐m rotor diameter, while designs of 10 MW turbines with >200‐m rotor diameter have been presented . These turbines are specifically designed to optimize energy yield at offshore locations .…”

Section: Introductionmentioning

confidence: 94%

Do we really need rotor equivalent wind speed?

Sark

Velde

Coelingh³

et al. 2019

Wind Energy

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The use of the rotor equivalent wind speed for determination of power curves and annual energy production for wind turbines is advocated in the second edition of the IEC 61400-12-1 standard. This requires the measurements of wind speeds at different heights, for which remote sensing equipment is recommended in addition to meteorological masts. In this paper, we present a theoretical analysis that shows that the relevance of the rotor equivalent wind speed method depends on turbine dimensions and wind shear regime. For situations where the ratio of rotor diameter and hub height is smaller than 1.8, the rotor equivalent wind speed method is not needed if the wind shear coefficient at the location of the wind turbine has a constant value between −0.05 and 0.4: in these cases, the rotor equivalent wind speed and the wind speed at hub height are within 1%. For complex terrains with high wind shear deviations are larger. The effect of non-constant wind shear exponent, ie, different wind shear coefficients for lower and upper half of the rotor swept area especially at offshore conditions is limited to also about 1%. KEYWORDSLiDAR, power curve, remote sensing, rotor equivalent wind speed, wind shear of the turbines, the ratio of rotor diameter and hub height is smaller than 1.5. ---This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

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“…It is therefore necessary to develop higher‐fidelity tools to simulate such cases and use the obtained knowledge to improve/calibrate the fast engineering tools. This necessity has been highlighted by the wind energy community in recent years . Fully resolved CFD applied to wind turbine rotors has been developed for many years now, becoming a mature and trusted tool.…”

Section: Introductionmentioning

confidence: 99%

Vortex simulations of wind turbines operating in atmospheric conditions using a prescribed velocity‐vorticity boundary layer model

et al. 2018

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A prescribed velocity-vorticity boundary layer model for the vorticity transport equation is proposed, which corrects the unphysical upward deflection of the wake seen in a simpler prescribed velocity shear approach. A Lagrangian implementation of the boundary layer model has been investigated using our in-house vortex solver MIRAS. The MIRAS code contains both an aerodynamic part and a structural-mechanical part taking into account aeroelastic phenomena. The solver is employed to simulate flows around wind turbines and uses a combination of filaments and particles in order to mimic the vorticity released by the wind turbine blades. The vorticity is interpolated onto a uniform Cartesian mesh, where the interaction is efficiently calculated by an fast Fourier transform-based method. Simulations of wind turbines operating in an atmospheric boundary layer flow are carried out and analysed in detail for a range of scenarios. The manuscript focuses on studying the influence of wind shear and turbulence, which is varied to mimic natural atmospheric conditions. A traverse virtual probe up to 30 diameters downstream of the rotor plane is used to investigate the properties of the turbulent wake flow for the different cases.This includes mean and standard deviation of the streamwise velocity component, wake deficit, Reynolds stresses, and power spectral density of the velocity signal. The results show that combining a prescribed boundary layer approach with a vortex method gives consistent and physically correct results if properly implemented. KEYWORDS aeroelasticity, atmospheric boundary layer, turbulence, vortex method, wind shear, wind turbine INTRODUCTIONVortex methods initially entered the wind energy community as a more physically accurate alternative to the basic Blade Element Momentum method (BEM) technique, which is based on 1-dimensional momentum theory and aimed to be used for rotor design. However, vortex methods have quickly developed in recent years and now can be seen as an advanced and matured tool capable of performing high-fidelity simulations of 1 or more turbines. Vortex methods are not only of interest during the actual rotor design process but also as analysis tool to investigate more complex scenarios, including aeroelastic, turbulent inflow, and shear effects. [1][2][3][4][5][6] Vortex solvers can be combined with different aerodynamic models depending on the degree of complexity required. Enumerated in ascending complexity, they can be classified as lifting line (LL) vortex lattice, potential panel method, and viscous-inviscid panel method. The latter class being the more physically correct, since it resolves the actual geometry of the blade accounting for the viscous effects enclosed inside the boundary layer.The present paper focuses on the lower degree of fidelity in terms of aerodynamic modeling of the wind turbine blades, using the LL approach. With the LL model, the rotor blades are represented by discrete filaments, which account for the bound vortex strength and release vorticity into the ...

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AVATAR: AdVanced Aerodynamic Tools of lArge Rotors

Cited by 15 publications

References 12 publications

Prospects for generating electricity by large onshore and offshore wind farms

Prospects for generating electricity by large onshore and offshore wind farms

Do we really need rotor equivalent wind speed?

Vortex simulations of wind turbines operating in atmospheric conditions using a prescribed velocity‐vorticity boundary layer model

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