Studies on Horizontal Axis Wind Turbine with Passive Teetered Brake and Damper Mechanism : (Relationship between Braking Effect of Rotor Blade and Flow Patterns around Rotor)

Abstract

This paper describes the development of passive system to control the output of horizontal axis wind turbine with teeter and feather mechanism of the blade. When the power generation system with variable speed is applied to the horizontal axis wind turbine, the rotaion speed of rotor increases with the wind speed. This mechanism can suppress the excessive input power in case of excessive wind speed more than the rated wind speed. This mechanism has two kinds of blade motions which are the teetering and the feathering motions. Both motions are coupled together by the special parts. When the blade is teetered downstream, the pitch angle of the blade (feathering angle) is changed to increase the attack angle. Also, these two kind of motions are supported by the spring and the damper which are attached to the mechanism. In this paper the relationships between the ratio of teetering and feathering angles and the braking effect of wind turbine are investigated experimentally. As the result, it is found that the braking effect for rotor is more excellent when the ratio of feathering and teetering is large. Also, the flow pattern around wind turbine is measured by LDV with two dimensions and visualized by tuft grid method and fog method using Laser sheet. It is found that the suppress phenomena of excessive rotation speed is caused by a couple of ring vortices, which are appeared on the area of blade tip side.