Environmental Engineering Reference
In-Depth Information
CHAPTER 8
wind turbines
Paul Cooper
School of Mechanical, Materials and Mechatronic Engineering,
University of Wollongong, NSW, Australia.
Vertical-axis wind turbines (VAWTs) have been demonstrated to be effective
devices for extracting useful energy from the wind. VAWTs have been used to
generate mechanical and electrical energy at a range of scales, from small-scale
domestic applications through to large-scale electricity production for utilities. This
chapter summarises the development of the main types of VAWT, including the
Savonius, Darrieus and Giromill designs. A summary of the multiple-streamtube
analysis of VAWTs is also provided to illustrate how the complex aerodynamics of
these devices may be analysed using relatively straightforward techniques. Results
from a double-multiple-streamtube analysis are used to illustrate the details of the
performance of VAWTs in terms of turbine blade loads and rotor power output as
a function of fundamental parameters such as tip speed ratio. The implications for
VAWT design are discussed.
1 Introduction
Vertical-axis wind turbines (VAWTs) come in a wide and interesting variety of
physical confi gurations and they involve a range of complex aerodynamic char-
acteristics. Not only were VAWTs the fi rst wind turbines to be developed but they
have also been built and operated at a scale matching some of the biggest wind
turbines ever made. VAWTs in principle can attain coeffi cients of performance,
C
p ,max
, that are comparable to those for horizontal-axis wind turbines (HAWTs)
and they have several potentially signifi cant advantages over the HAWTs.
These advantages include the fact that VAWTs are cross-fl ow devices and
therefore accept wind from any direction. Thus, in principle, they do not need a
yaw mechanism to ensure that they are aligned to the wind as is the case with all
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