Abstract
Small Darrieus Vertical-Axis Wind Turbines (VAWTs) are presently seen as a relevant research topic for the wind energy community, since they are thought to perform better than horizontal-axis rotors in the complex and highly-turbulent flow typical of the urban environment. Indeed, a preliminary wind tunnel test campaign on a H-Darrieus VAWT showed a significant increase of the performance for high turbulence levels. The present study analyses in detail the near wake of the turbine in the same turbulent conditions, enabling a better insight on the reasons of this power increase, and on the means to take advantage of it. Near-wake measurements are also benchmarked with a CFD simulation of the entire wake, in order to match the experimental wake measurements with the detachment of flow structures observed in CFD simulations. By doing so, a deeper and useful insight on the reasons why VAWTs perform better in turbulent environments is gained.
Highlights
Even though the majority of studies in wind energy are presently being devoted at designing larger and larger rotors (e.g. [1]), there is a significant interest arising on very small rotors for decentralized power production in the urban environment [2]
Small Darrieus Vertical-Axis Wind Turbines (VAWTs) are presently seen as a relevant research topic for the wind energy community, since they are thought to perform better than horizontal-axis rotors in the complex and highly-turbulent flow typical of the urban environment
The results are compared with the values coming from computational fluid dynamics (CFD) simulations described in subsection 2.2
Summary
Even though the majority of studies in wind energy are presently being devoted at designing larger and larger rotors (e.g. [1]), there is a significant interest arising on very small rotors for decentralized power production in the urban environment [2]. New focus must be put on a better understanding of the physics of wind turbines under the complex inflow conditions (especially in terms of flow misalignment and turbulence levels) that are typical of similar installations [3]. Small Vertical-Axis Wind Turbines (VAWTs) are considered probably the most promising solution for the urban environment [4]. Despite their lower peak performance, some specific features like omnidirectionality, lower noise emissions and pleasant aesthetic appearance [5] have made them a valuable alternative to conventional Horizontal-Axis Wind Turbines (HAWTs) in urban applications [6,7]. A careful analysis of these conditions is mandatory for this technology to reach maturity and economic viability within an acceptable time horizon
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