Combined experimental and numerical study on the near wake of a Darrieus VAWT under turbulent flows

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.