A combined experimental and numerical analysis of the wake structure and performance of a H-shaped Darrieus wind turbine

The Darrieus concept is increasingly welcome by both researchers and manufacturers of wind turbines, especially in view of small-size installations in the built environment or large-scale offshore rotors mounted on floating platforms. To achieve a more efficient, structurally sound and cost-effective design of Darrieus Vertical Axis Wind Turbines, numerical techniques making use of Computational Fluid Dynamics are considered as the most promising tool, since they provide a detailed and comprehensive representation of the flow, which is instrumental for the understanding of the unsteady aerodynamics of the rotor. In this study, a two-dimensional U-RANS computational model was applied to analyze both the overall performance and, especially, the wake characteristics on the mid plane of a H-shaped Darrieus VAWT for microgeneration. The turbine was studied experimentally in a large-scale, open-jet wind tunnel, including both performance and wake measurements, in the frame of a comprehensive activity oriented to the construction of an experimental benchmark for VAWT simulations. Thanks to the availability of such a unique set of experimental data, systematic comparisons between simulations and experiments were carried out, highlighting the main aerodynamic phenomena and flow macro-structures and discussing the prediction capabilities of the numerical model. On these bases, the present study is considered of interest for the scientific community working in this field, especially as a first support to future analyses aimed at improving the understanding of the unsteady aerodynamics taking place past Darrieus wind turbine blades.