Abstract
Due to the rapid progress in high-performance computing and the availability of increasingly large computational resources, Navier–Stokes (NS) computational fluid dynamics (CFD) now offers a cost-effective, versatile, and accurate means to improve the understanding of the unsteady aerodynamics of Darrieus wind turbines and deliver more efficient designs. In particular, the possibility of determining a fully resolved flow field past the blades by means of CFD offers the opportunity to both further understand the physics underlying the turbine fluid dynamics and to use this knowledge to validate lower-order models, which can have a wider diffusion in the wind energy sector, particularly for industrial use, in the light of their lower computational burden. In this context, highly spatially and temporally refined time-dependent three-dimensional (3D) NS simulations were carried out using more than 16,000 processor cores per simulation on an IBM BG/Q cluster in order to investigate thoroughly the 3D unsteady aerodynamics of a single blade in Darrieus-like motion. Particular attention was paid to tip losses, dynamic stall, and blade/wake interaction. CFD results are compared with those obtained with an open-source code based on the lifting line free vortex wake model (LLFVW). At present, this approach is the most refined method among the “lower-fidelity” models, and as the wake is explicitly resolved in contrast to blade element momentum (BEM)-based methods, LLFVW analyses provide 3D flow solutions. Extended comparisons between the two approaches are presented and a critical analysis is carried out to identify the benefits and drawbacks of the two approaches.
Highlights
The deployment of Darrieus-type Vertical-Axis WindTurbines (VAWTs) is rapidly growing due to the significant benefits in comparison to more conventional horizontal-axis rotors in applications such as delocalized power production in the urban environment, offshore floating turbines and tidal energy applications
One of the previous studies based on 2D Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) for a 3-blade rotor showed that temporal and spatial grid-independent solutions are obtained provided that grids with at least 400,000 elements are used [9]
CFD results are here used as a benchmark to verify the computationally less expensive Lifting Line Free Vortex Wake Model (LLFVW) method
Summary
The deployment of Darrieus-type Vertical-Axis WindTurbines (VAWTs) is rapidly growing due to the significant benefits in comparison to more conventional horizontal-axis rotors in applications such as delocalized power production in the urban environment, offshore floating turbines and tidal energy applications. One of the previous studies based on 2D RANS CFD for a 3-blade rotor showed that temporal and spatial grid-independent solutions are obtained provided that grids with at least 400,000 elements are used [9]. To preserve the same accuracy level in a 3D simulation of the same turbine (modelling only half of the rotor making use of symmetry boundary conditions on the plane at rotor midspan) the 3D mesh would consist of about 90,000,000 cells, which is almost ten times the size of the finest meshes used in the 3D RANS studies of Darrieus rotor flows published to date.
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