Darrieus turbines: The physics of self-starting

As the demand for renewable energy grows, the use of small wind turbines becomes increasingly attractive. Turbines using vertical-axis geometries are particularly suited to the urban environment by virtue of their operation being independent of wind direction. However, such designs have received much less attention than the more common ‘propeller type’ designs and the understanding of some aspects of their operation remains weak. This is particularly true of their starting characteristics. Indeed, some authors maintain that they cannot start without external assistance. In this investigation a numerical model is used to simulate the starting of an H-rotor Darrieus turbine under steady wind conditions. Experimental wind-tunnel data for a small prototype is presented, demonstrating unaided start-up of a three-bladed Darrieus in a steady wind. Discrepancy between the modelled and experimental results demonstrate that modelling remains constrained by the quality of data on aerofoil characteristics.