The majority of present-day horizontal axis wind turbine blade tips are simple
designs based on historical trends. There is, however, some evidence that varying the
design of the tip can result in significant changes in performance characteristics such
as power output, noise, and structural loading. Very few studies have tested this idea
on an actual rotating blade and there is much to be investigated. Thus, a project was
devised to examine experimentally the effect of various tip designs on an operational
rotating wind turbine rotor.
A tapered, twisted blade 1.6 m in length was custom designed for use in the UW
Wind Energy Research Facility using the blade element momentum (BEM) method.
A coupling mechanism was designed such that the outer 10% of each blade could be
exchanged to evaluate the effect of different tip designs. A set of three blades was
fabricated out of fibre-reinforced plastic, while the tips were machined out of maple
wood on a CNC milling machine.
The blade was evaluated with a standard rectangular tip to establish baseline
performance against which to compare the alternative tip configurations. The three-bladed
rotor was tested at shaft speeds from 100 rpm to 240 rpm in wind speeds
up to the facility maximum of 11.1 m/s. The rotor was found to have a maximum
power coefficient of 0.42 at a tip speed ratio of 5.3 and a 1.45 kW rated power at a
wind speed of 11 m/s. The performance was compared to predictions made using the
BEM method with airfoil data generated using a modified Viterna method and the
Aerodas method. While the Aerodas data was capable of predicting the power fairly
accurately from 5 m/s to 10 m/s, the modified Viterna method predicted the entire
curve much more accurately.
Two winglet designs were also tested. The first (called Maniaci) was designed
by David Maniaci of Pennsylvania State University and the other (called Gertz) was
designed by the author. Both winglets were found to augment the power by roughly
5% at wind speeds between 6.5 m/s and 9.5 m/s, while performance was decreased
above and below this speed range. It was calculated that the annual energy production
could be increased using the Maniaci and Gertz winglets by 2.3% and 3%, respectively.
Considering the preliminary nature of the study the results are encouraging and it is
likely that more optimal winglet designs could be designed and evaluated using the
same method. More generally, this study proved that the blades with interchangeable
tips are capable of being used as an evaluation testbed for alternative wind turbine
blade tip designs.
| Identifer | oai:union.ndltd.org:WATERLOO/oai:uwspace.uwaterloo.ca:10012/5941 |
| Date | January 2011 |
| Creators | Gertz, Drew Patrick |
| Source Sets | University of Waterloo Electronic Theses Repository |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
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