Start-up behavior of a three-bladed h-Darrieus VAWT: experimental and numerical analysis

Despite increasing attention paid by both the industrial and the academic worlds, an effective diffusion of Darrieus wind turbines is still hindered by productivity lower than that of classical HAWTs, mainly connected to the critical behavior of these machines during the transient phases and in particular, during the start-up transitory, which has not been investigated in depth in the past. In this paper, a numerical code for the evaluation of the transient behavior of H-Darrieus turbines is presented. The time-dependent code was based on a theoretical approach derived from the Momentum Models and completed by several sub-models for the evaluation of the main secondary and parasitic effects. The new software was validated with an extended experimental campaign in a wind tunnel on a three-bladed H-Darrieus turbine, obtaining constant agreement with experimental data. A sensitivity analysis was then performed in order to investigate the start-up behavior of a generic small size three-bladed H-Darrieus rotor. In particular, for a fixed turbine layout, the influence of the airfoil type and the blade shape on the startup capabilities of the rotor was investigated as a function of the initial position of the rotor and the oncoming wind velocity.