Abstract
In order to improve the reliability of megawatt wind turbines, the passive teetered brake & damper mechanism is applied. Its two unique effects, as its name implies, are braking and damping. The passive brake & damper mechanism is useful for variable speed control of the large wind turbine. It is comprised of teetering and feathering mechanisms. When the wind speed exceeds the rated wind speed, the blade is passively teetered in a downwind direction and, at the same time, a feathering mechanism, linked to toe teetering mechanism through a connecting rod is activated. In this study, two kinds of blades, a twisted tapered blade and a non-twisted rectangular one, are used with this passive mechanism. Testing of the model horizontal axis wind turbine in a wind tunnel showed that the passive mechanism can suppress the over-rotational speed of the rotor. The velocity distribution around the rotating blade is measured by a two-dimensional laser Doppler velocity meter. It is found that the passive teetered brake & damper mechanism can suppress the over-rotational speed of the rotor, and the braking effect is caused by the reduction of the angle of inflow for the blade.
