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Seth Bright
Dustin Dvorak
Kurt Joob
March 15, 2013
Wind Turbine Blade Shape
Abstract
This report represents the effects of the blade shape on the efficiency of a turbine. The
experiment tested the efficiency of a wind turbines blade shape by comparing the power from the
wind and the power generated from the turbine. From previous experiments we gathered
understanding that a lower angle of blade pitch produces the maximum blade speed and therefore
the maximum voltage, amperage and power. The range between 10 degrees and 30 degrees
produced the maximum power output for the turbine depending on the load applied to the
turbine. When testing to maximize our wind turbine’s efficiency we used blade pitch as the
independent variable and kept all others constant. With a blade pitch of approximately 12
degrees we achieved an efficiency of 0.63%. After some post-experiment changes we increased
our efficiency to 2.24%.
Introduction
Wind power is just one of the many forms of clean renewable energy that engineers and scientist
are exploring as replacements for our dependency for fossil fuels. This experiment was designed
to test our group’s skills to conceptualize, design, and construct a wind turbine with the highest
efficiency possible. Despite their limitations due to the inconsistency of wind, turbines are
helping the world to harness clean and renewable energy. According to the U.S. Department of
Energy, they want to transition to 20% wind power by 2030. Denmark has already reached 21%
of stationary electric power from wind turbines and produced over 10 TW/h of electricity in
2012. With many countries turning to alternate energy sources as commercial sources of power
the demand for engineers is also increasing in this field. Our experimentation is just a small scale
application of the principles being utilized by professionals. This experiment gave our group a
good understanding of the physical properties that govern how wind turbines work. This
experiment is built off of the previous lab experiments with wind turbines. We took the
knowledge gained from previous experimentation and applied it to our design. This experiment
was performed at Crafton Hills Community College as part of the Introduction to Engineering
course taught by Corey Harden in the Spring Semester 2013. With the goal of efficiency in mind,
our team designed a machine that minimized the turbulence of the blades which we thought
would have the largest effect on efficiency. Our group prediction was that a smooth teardrop
shape would be our best option. The major concern of our design was that the mass moment of
inertia of our blades was too large.
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Procedures
The materials for the test consisted of a KidWind Turbine, plastic and balsa wood blades, a blade
pitch gauge, a Lasko house fan, and a digital multi-meter to measure output in volts and amps.
The fan was placed approximately four and a half feet away from the turbine and was held
approximately one and a half feet in the air by a waste disposal bin. The fan was placed on the
third setting (high) for wind testing. A wind-meter was also used in order to standardize wind
speed. The wind speed used by all teams when testing was approximately 5 mph (miles per
hour). The wind speed was measured using a hand-held wind meter. The measurement was taken
with the wind meter held so that the centers of both the wind meter and the fan were concentric.
The initial stages of testing were already completed in earlier tests and focused on determining
wind turbine performance in reference to blade pitch. This experiment was to focus on blade
shape rather than pitch so we changed the pitch only after the shape was finalized to test for
optimal efficiency. To obtain the efficiency of the wind turbine we used the formula:
Equation 1)
ɳ = Output power (W) / Input Power (W) *100
where ɳ is the efficiency (percentage form)
To calculate the efficiency of our blade design we needed to individually calculate the input
power provided by the fan and the output of the turbine measured by a multi-meter. The input
power from the wind is calculated using the formula:
Equation 2)
Pw = (1/2)ρAv3
where Pw is the power of wind (W)
ρ is the air density (kg/m3)
A is the swept area if blades (m2)
v is the air velocity (m/s)
The output power from the wind turbine can be calculated using the formula:
Equation 3)
P=IV
where P is the power (W)
I is the current (A)
V is the Voltage (V)
A multi-meter was used to collect both the current and voltage while using a 10 Ohm resistor. A
diagram of the two possible blade shapes we came up with is in Figure 1. We choose to complete
the experiment with Design 2. We chose the second design after researching various blade
shapes and deciding that Design 2 would produce less turbulence than Design 1.
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Figure 1
Results/Discussion
The results that we obtained from testing showed a relatively low efficiency but it was still onpar with our peers. We achieved .63% efficiency with our initial design. We calculated a Pw of
4.0 W by using an air density value of 1.112kg/m3, a swept area of .679m2, and a wind velocity
of 2.24m/s. We calculated an output power of 0.025 W by measuring a current of 0.05A and a
voltage of 0.5V. After completing our final test we decided that our initial concern was more
apparent after testing than before. We chose to decrease the radius of each of the 3 blades by
10.5cm which reduced the swept area from 0.679m2 to 0.407m2. By reducing the length of each
blade significantly reduced the mass moment of inertia of the turbine as a whole. The smaller
swept area produces a smaller Pw value of 2.5W, a 37.5% decrease in the power received from
the wind. By reducing the mass moment of inertia we were able to get a higher blade speed and
therefore higher values for current and voltage. We calculated an output power of .056W
compared to the 0.025W at full length, a 124% increase in power output. Using our new values
we achieved an efficiency of 2.24%. This is 250% higher than our original efficiency. Almost
double the efficiency that our peers were obtaining. This shows that a single change can greatly
impact both the input and output power causing an even larger change in efficiency.
Conclusion
Our research team predicted that turbulence of the blades would be a major factor in the overall
efficiency of the turbine. Our class showed a pretty even distribution between 0.25% and 1.5%
efficiency with only a few groups getting above 1.0%. A fairly accurate prediction of efficiency
could be made with a brief overview of each team’s turbine. Comparing our initial results with
those of the class put us somewhere in the middle of the groups. After we made some final
changes we reached almost double the efficiency of the next closest team. Due to the random
selection of what team would be observed first gave some teams more time to make adjustments
and to maximize efficiency. We retested ourselves after reducing the length of our blades for our
own gratification and satisfaction.
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Works Cited
Lund, Henrik et al (2010-02-19). Danish Wind Power Export and Cost. Department of
Development and Planning, Aalborg University. ISBN 978-87-91830-40-2. 13 March
2013.
Zichal, Heather. A Record Year for the American Wind Industry. U.S. Department of energy.
2013. Web. March 13, 2013.