Investigation of Passive Blade Cyclic Pitch Variation Using an Automatic Yaw Control System: A Subcontract Report

The purpose of this study was to determine by analysis and full-scale experiments, whether a two-bladed wind turbine rotor with passive cyclic pitch variation, automatically yawed for rotor torque and speed control, is potentially cost-effective for wind energy conversion. A simple mechanism for obtaining passive cyclic pitch variation, adapted from rotorcraft technology, eliminates transfer ofgyroscopic moments from simultaneous blade coning and flapping. Thus, as a result of the suppression of blade flapping by passive cyclic pitch variation rapid yaw rates without vibratory hub moments or appreciable out-of-plane blade excursions are feasible for two-bladed rotors with substantial blade elastic coning. A 7.6-m diameter vane-stabilized wind turbine rotor of low solidity was testedwith both passive and active automatic furl control systems and with both a variable speed alternator and a constant speed induction generator. The tests were support by a yaw dynamics analysis. Within the tested performance envelope, the rotor ran smoothly with good performance and without excessive vibrations or loads even at high yaw angles and yaw rates. The passive automatic furl controlappeared to be the more desirable configuration for both variable speed alternators and constant speed induction.