Development and evaluation of passive variable-pitch vertical axis wind turbines

摘要

Vertical-axis wind turbines do not need to be oriented to the wind direction andoffer direct rotary output to a ground-level load, making them particularly suitablefor water pumping, heating, purification and aeration, as well as stand-aloneelectricity generation. The use of high-efficiency Darrieus turbines for such applicationsis virtually prohibited by their inherent inability to self-start. The provisionof blade-articulation (variable-pitch blades) has been demonstrated by a numberof researchers to make Darrieus turbines self-starting. One aim of this thesisis to evaluate the various concepts manifested in the numerous specific passivevariable-pitch designs appearing in the literature, often without theoretical analysis.In the present work, two separate mathematical models have been producedto predict the performance of passive variable-pitch Darrieus-type turbines. Ablade-element/momentum theory model has been used to investigate the relationshipsbetween the key parameter values and turbine steady-state performance. Astrategy for parameter selection has been developed on the basis of these results.A free vortex wake model for passive variable-pitch turbines has been developed,allowing the study of unsteady performance. Significant reduction of average ef-ficiency in a turbulent wind is predicted for a Darrieus turbine. The improvedlow-speed torque of passive variable-pitch turbines is predicted to significantlyimprove turbulent wind performance.Two new design concepts for passive variable-pitch turbines are presented thatare intended to allow greater control of blade pitch behaviour and improved turbulent wind performance. A prototype turbine featuring these design conceptshas been designed, constructed and tested in the wind tunnel. As part of thistesting, a technique has been developed for measuring the pitch angle response ofone of the turbine blades in operation. This allows comparison of predicted andmeasured pitch histories and gives insight into the performance of turbines of thistype. Results have demonstrated the usefulness of the mathematical models asdesign tools and have indicated the potential of one of the new design concepts inparticular to make a vertical axis wind turbine self-starting.