Observations of the starting behaviour of a small horizontalaxis wind turbine

This paper describes observations of the starting performance of a small horizontal-axis wind turbine in the context of a simple, quasi-steady analysis of the complex aerodynamics dominated by unsteadiness, high angles of attack, and low Reynolds number. Soon after they begin rotating, the blades can generate unexpectedly high torque. At the same time, the nondimensional pitch rate and reduced frequency are too small to suggest a significant increase of the torque through the effects of unsteadiness. The torque then decreases due to inappropriate blade angles of attack. This leads to a substantial “idle time” at both high and low wind speed, in which the rotating blades are accelerating only slowly and the angles of attack are slowly decreasing. When the angles are reduced to those giving high lift: drag ratios, the blades accelerate rapidly to complete the starting sequence by producing significant amounts of power. At low wind speeds, about 4 m/s, a gust is apparently required to complete the starting sequence.