Download files
Abstract
Vertical-axis wind turbines do not need to be oriented to the wind direction and
offer direct rotary output to a ground-level load, making them particularly suitable
for water pumping, heating, purification and aeration, as well as stand-alone
electricity generation. The use of high-efficiency Darrieus turbines for such applications
is virtually prohibited by their inherent inability to self-start. The provision
of blade-articulation (variable-pitch blades) has been demonstrated by a number
of researchers to make Darrieus turbines self-starting. One aim of this thesis
is to evaluate the various concepts manifested in the numerous specific passive
variable-pitch designs appearing in the literature, often without theoretical analysis.
In the present work, two separate mathematical models have been produced
to predict the performance of passive variable-pitch Darrieus-type turbines. A
blade-element/momentum theory model has been used to investigate the relationships
between the key parameter values and turbine steady-state performance. A
strategy 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 improved
low-speed torque of passive variable-pitch turbines is predicted to significantly
improve turbulent wind performance.
Two new design concepts for passive variable-pitch turbines are presented that
are intended to allow greater control of blade pitch behaviour and improved turbulent wind performance. A prototype turbine featuring these design concepts
has been designed, constructed and tested in the wind tunnel. As part of this
testing, a technique has been developed for measuring the pitch angle response of
one of the turbine blades in operation. This allows comparison of predicted and
measured pitch histories and gives insight into the performance of turbines of this
type. Results have demonstrated the usefulness of the mathematical models as
design tools and have indicated the potential of one of the new design concepts in
particular to make a vertical axis wind turbine self-starting.