OBSERVATIONS OF THE STARTING BEHAVIOR OF A SMALL HORIZONTAL-AXIS WINDTURBINE

This paper describes observations of the starting performance of a sma ll horizontal-axis wind turbine in the context of a simple, quasi-stea dy analysis of the complex aerodynamics dominated by unsteadiness, hig h angles of attack, and low Reynolds number. Soon after they begin rot ating, the blades can generate unexpectedly high torque. At the same t ime, the non-dimensional pitch rate and reduced frequency are too smal l 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 hi gh and low wind speed, in which the rotating blades are accelerating o nly slowly and the angles of attack are slowly decreasing. When the an gles are reduced to those giving high lift:drag ratios, the blades acc elerate rapidly to complete the starting sequence by producing signifi cant amounts of power. At low wind speeds, about 4 m/s, a gust is appa rently required to complete the starting sequence. (C) 1997 Elsevier S cience Ltd.