E-project-032714-164435 - PPM MQP 1342 E-project-032814-091749 - DM3 MQP AAFO E-project-032814-094103 - BJS MQP 1342 Design of an Alternative Hybrid Vertical Axis Wind Turbine A Major Qualifying Report Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE In partial fulfillment of the requirements for the Degree of Bachelor of Science By: Date: March 28, 2014
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Design of an Alternative Hybrid Vertical Axis Wind Turbine
A Major Qualifying Report Submitted to the Faculty of the
WORCESTER POLYTECHNIC INSTITUTE
In partial fulfillment of the requirements for the
Degree of Bachelor of Science
By:
Date: March 28, 2014
i
Abstract
The goal of this project was to design a vertical axis wind turbine for urban use.
Throughout this project, wind velocities were monitoring using anemometers located on
buildings at Worcester Polytechnic Institute. Using the analyses of wind velocities in this
urban location and evaluations of different turbine types with respect to these wind
characteristics, it was determined that a new type of turbine should be created. It was
determined that a turbine that incorporated both lift and drag would be beneficial. The
design of this turbine included airfoils along with a shroud for protection and increased
wind velocities. The overall design was created, manufactured, and tested.
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Capstone Design Experience ABET Requirement
To fulfill the requirements for a Major Qualifying Project (MQP), this project must
meet the requirements for a capstone design experience. The Accreditation Board for
Engineering and Technology (ABET) defines this as an “experience based on the knowledge
and skills acquired in earlier course work and incorporating engineering standards and
realistic constraints that include most of the following considerations: economic;
environmental; sustainability; manufacturability; ethical; health and safety; social; and
political”1. For this project, a vertical axis wind turbine was designed, which included
airfoils, a shroud, a cam track, and a mounting system. The following considerations were
included in the design.
Economic
This project was completed with several economic considerations in mind. The
turbine was made out of inexpensive materials, most of which can be purchased locally.
Since small turbines do not create a large amount of electricity, this turbine must be
inexpensive in order for its electricity generation to offset the purchase cost over time.
This fact heavily influenced design and materials decisions.
Environmental/Sustainability
The burning of fossil fuels is not a sustainable way to generate energy, and it has
been causing great harm to the environment. Any contribution to the field of green energy,
such as wind turbines, can help to shift energy production away from fossil fuels and
toward renewable resources. This turbine is designed for small scale, urban applications,
1 (Worcester Polytechnic Institute n.d.)
iii
which is not a place where they are currently utilized to any significant degree. Expanding
this market would decrease cities’ reliance on traditional energy sources, creating a more
sustainable and environmentally friendly energy environment there.
Manufacturability
Manufacturability was taken into consideration for every aspect of the design. The
ease and cost of manufacturing, as well as the availability and cost of materials, all
influenced design decisions. The turbine has potential to be created by any person with
some degree of mechanical aptitude because of its simplistic design.
Health and Safety
Health and safety were also considered in the design. One reason for the addition of
the shroud was to improve the safety of the turbine by enclosing all of the moving parts.
Decisions on materials included thought of their safety and toxicity, and the less harmful
options were chosen. Also, an airfoil was chosen which would not increase its speed
greatly in high winds, thereby lowering the risk of the turbine breaking during storms.
Fulfillment of Majors
This report represents the work of three WPI undergraduate students submitted to
the faculty as evidence of completion of a degree requirement. The members of this project
consisted of an Environmental Engineer, a Physics/Civil Engineer, and a Mechanical
Engineer. Below is the breakdown of how it satisfied each of the majors.
Civil and Environmental Engineering
The major aspects of this project that related to Civil and Environmental
Engineering included wind analysis and turbine design. The wind analysis consisted of data
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collection from the anemometers and data analysis with Microsoft Excel and WAsP. Wind
patterns were discerned for this urban environment, and were taken into consideration in
the turbine design. In addition, the positive environmental impact of using turbines instead
of fossil fuels goes along with the civil and environmental engineering major. Turbines like
the one designed in this project would help expand the market for renewable wind energy
and help to decrease the need for fossil fuels.
Engineering Physics
Almost all aspects of this project related to Engineering Physics, including the wind
analysis and the examination of turbine, airfoil and shroud designs. The movement of air in
the atmosphere (wind), as well as around objects like airfoils and shrouds, are all complex
events described by physics. These concepts were combined with engineering tasks such
as shroud design and CFD analysis, airfoil evaluation, and design of the cam track.
Mechanical Engineering
The aspects of this project that related to Mechanical Engineering include the
overall design and construction of the turbine, shroud, and airfoils. The design of the
airfoils was done using fluid mechanics, and the manufacturability of the airfoils was done
using engineering mechanics. The design of the turbine required analyses involving
engineering mechanics, and the design of the shroud required analyses involving fluid
mechanics. Major engineering components included airfoil evaluation and overall
manufacturing of the turbine, along with with the modeling of the turbine and mounting
system for manufacturing purposes.
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Acknowledgements
We would like to thank: Professors Paul Mathisen, Brian Savilonis, and David Medich For their guidance, leadership and involvement throughout this project. Don Pellegrino For his guidance with equipment, data collection, and expertise in the wind lab and how it works. Alessandro Aquadro For all of his hard work and hours spent manufacturing. Francis X. Reilly Sr. For inspiring this project and allowing for us to see his creations.
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Table of Contents Introduction .......................................................................................................................................... 1
1.1 Problem ......................................................................................................................................... 2
1.2 Goal, Objectives, and Approach .................................................................................................... 3
2.3 Wind Power Availability ................................................................................................................ 6
2.4 Current Use of Wind Power .......................................................................................................... 9
2.5 WAsP ........................................................................................................................................... 10
Introduction Traditional energy sources, such as non-renewable coal and oil, are burned to
produce energy. This process creates a negative impact on the environment, primarily
through the release of greenhouse gases and, to a smaller extent, toxic gases. These gases
can affect the climate and the air quality of the Earth. Because these fossil fuels are being
depleted, the principal investigators are exploring the use of green energy as an alternative
to non-renewable energy resources.
Green energy or Eco energy are terms used to describe energy produced or
generated by natural, renewable resources that cause minimal negative impacts to the
environment. Wind, solar, geothermal, hydro, and bio energy are all considered green.
Green energy involves generating power from natural phenomena like wind, sunlight, tides,
plants and geothermal heat generated deep within the earth. For example, wind power can
be harnessed by allowing the wind to rotate turbines, and converting the rotational energy
to electricity. Large turbines can be connected to a system where power is collected, stored
and distributed, in some cases powering entire communities. Sustainable alternatives and
green energy resources account for almost 16 percent of global energy consumption today
and are growing steadily2.
Clean energy resources use the Earth’s natural energy flows, which cause minimum
negative environmental impact. Developing green energy mainly aims at generating power
while creating minimal waste and pollution. The globally changing economic and
environmental conditions have forced some nations and organizations to rearrange their
2 (Green Energy From Natural and Renewable Resources 2013)
2
strategies, moving slowly away from the conventional burning of fossil fuels and working
towards a lower carbon existence. The primary goal of developing and promoting
alternative, renewable sources of energy is to reduce energy costs and greenhouse gas
emissions3.
1.1 Problem
While progress has been made to advance the technology required to create an
efficient large-scale wind turbine, such turbines cannot be used in all locations due to space
and financial limitations. In these areas, more affordable turbines, sized to power
individual homes, are necessary. Urban areas are excellent examples of space-limited
regions; here space is limited to the extent that a turbine must be mounted on roofs of
buildings. Such turbines are currently on the commercial market, however, they generally
are expensive and do not create sufficient power to offset the cost of such a device over its
lifetime. A rooftop turbine designed for an urban environment that is more efficient and
less costly to manufacture would be an excellent energy production option for
consumers. There is a need for such a turbine to be developed to allow residents in urban
areas a better renewable energy option.
Previous MQPs have investigated the practicality of shrouded Vertical Axis Wind
Turbines and VAWTs for urban use in general. One past MQP, Vertical Axis Wind Turbine
Evaluation and Design by Deisadze, et al. (2013), focused on the effect of a shroud on the
power output of simple Savonius and Darrieus turbine blades. The project also
investigated vibrations in the turbine and how those would be transmitted to a roof. In
another past MQP, Enclosed Wind Turbines by Brandmaier, et al. (2013), different shroud
3 (Green Energy From Natural and Renewable Resources 2013)
3
designs were compared on a turbine with flat blades. Neither of these MQPs investigated
blade design and both chose basic blades for testing4,5. Since the type, size, and particular
design of turbine blades has a large effect on the efficiency of a turbine, it is an area that
should receive further consideration6.
1.2 Goal, Objectives, and Approach
The goal of this project is to design and develop a vertical axis wind turbine (VAWT)
for urban residential use. The VAWT will be designed to operate in conditions with wind
patterns found in urban settings and will be sufficiently mechanically efficient to be a viable
option for consumers. While optimizing the VAWT for urban settings, special attention will
be paid to the type and design of the blades, since that is the most variable component of
the system. In order to accomplish this goal, the following objectives will be addressed:
1. Analyze wind patterns and characteristics in an urban environment.
2. Evaluate various turbine blade designs to predict which would be best for urban
households based largely on efficiency but also on the following factors:
vibrations, noise, esthetics, reliability, manufacturability and cost to build.
3. Determine the efficiency of the best blade design(s) by manufacturing them,
creating an experimental setup, and performing testing.
The background research on wind power availability, wind turbines, and wind
turbine blade design. The past MQPs were helpful in this regard, as they provided
information on wind patterns, along with general equations that will be used during the
initial investigation of blade types.
4 (Brandmaier, et al. 2013) 5 (Deisadze, et al. 2013) 6 (Ragheb and Ragheb, Wind Turbines Theory - The Betz Equation and Optimal Rotor Tip Speed Ratio 2011)
4
The collection and analysis of data from wind anemometers around the WPI campus
helped in characterizing wind patterns and determining which turbine types were worth
investigating. Since the design did not have to include a shroud, there was a wide range of
possibilities for blade types. Each was evaluated, taking not only efficiency into account
but also vibrations, noise, manufacturability, esthetics, reliability, and other factors. Then,
using this information, the best turbine was chosen and specific blade types were evaluated
for use in that turbine. Finally, the best complete turbine design was chosen, prototyped,
and tested in an outdoor environment to accurately evaluate its efficiency. The wind
analysis, design conclusions, and testing results can be found in Section 4.
5
Background The United States currently relies heavily on coal, oil, and natural gas for energy.
Fossil fuels are non-renewable and are becoming too expensive and environmentally
damaging to retrieve. There are a variety of alternative energy resources which are
renewable, such as wind and solar energy. These other resources are constantly
replenished and will never run out. Wind is a clean source of renewable energy that
produces no air or water pollution. This energy is needed to provide an alternative power
source for everyday life. Since the only major cost involved in producing energy from wind
is the initial construction and installation of the turbine, wind energy has the potential to
lower energy costs while it provides a more sustainable means of producing energy7.
2.1 Types of Renewable Energy
There are five main types of renewable energy: solar, geothermal, biopower, hydro
power, and wind8. These energy types will be the future to a cleaner more energy efficient
world.
Wind power captures the wind in the atmosphere and converts it into mechanical
energy then into electricity. There are three main types of wind power; utility-scale wind,
distributed or small wind, and offshore wind. Utility-scale wind describes wind turbines
larger than 100 kilowatts. The electricity from these turbines is delivered to a power grid
and distributed to the user by electric utilities or power system operators. Distributed wind
is wind which uses turbines of 100 kilowatts or smaller to directly power a home, farm or
7 (Wind 101: The Basics of Wind Energy 2013) 8 (Green Energy From Natural and Renewable Resources 2013)
6
small business for its primary use. Last, offshore wind is wind power that consists of wind
turbines that are set up in bodies of water around that world9.
2.2 Wind Farming
A wind farm is a group of wind turbines located in the same area and that are used
to produce energy. A large wind farm may consist of hundreds of individual wind turbines
and may cover hundreds of square miles, but the land between the turbines may be used
for agricultural or other purposes. Compared to the environmental impact of traditional
energy sources, the impact of wind power is relatively minor. Wind power consumes no
fuel and emits no air pollution. The energy needed to manufacture and transport the
materials required to build a wind farm is equivalent to the energy produced by the farm
after just a few months.
2.3 Wind Power Availability
New installations place the U.S. on a trajectory to generate 20 percent of the nation’s
electricity by 2030 solely from wind energy. Growth in 2008 put $17 billion into the
economy, positioning wind power as one of the leading sources of new power generation.
Wind projects completed in 2008 also accounted for about 42 percent of the entire new
power-producing capacity added in the U.S. during the year. Wind power in the U.S.
provides enough electricity to power the equivalent of nearly 9 million homes, avoids the
emissions of 57 million tons of carbon each year, and reducing expected carbon emissions
from the electricity sector by 2.5 percent10.
9 (RenewableEnergyWorld.com 2013) 10 (Wind 101: The Basics of Wind Energy 2013)
7
Figure 1 shows the predicted average annual wind speeds at a 30 meter height.
Areas with good exposure to prevailing winds and annual average wind speeds around 4
meters per second or greater at a 30 meter height are generally considered to have a
suitable wind resource for small wind projects. Small wind turbines are typically installed
between 15 and 40 meters high11.
Figure 1: United States Annual Average Wind Speed (30 Meters)12
Figure 2 shows the predicted average annual wind speeds at a height of 80 meters.
Areas with annual average wind speeds around 6.5 meters per second and greater at an 80
meter height are generally considered to have a wind resource suitable for wind
Table 2: Variables and Definitions for the CAM Track
Variable Definition
(x,y) = (0,0) The center of the turbine’s rotational axis Rrod The distance from the center of the turbine to the center of
the rod which attaches the blade to the turbine θ The angle of the Rrod vector L The radius of the follower α The ideal angle of attack for lift (angle between the blade and
the incident wind)
The drag and lift equations were inputted into Creo in order to begin creating the
complete path. The equation for the drag path was adjusted slightly in order to keep the
angle just below 90 degrees. This is because at 90 degrees, a blade could get stuck in a
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statically indeterminate state which would cause extra stress in the system that could lead
to failure. Once both of these tracks, seen in Figures Figure 28 Figure 29, were in Creo, a
complete track needed to be created based on them. This path would need to follow the lift
path while the blades travel into the wind, and then follow the drag path away from the
wind. On both the front and back of the turbine, there would be transition sections which
brought the follower smoothly from one path to the other. Figure 30 shows the full path
which was created, with the wind entering from above.
Figure 28: Lift Path
Figure 29: Drag Path
Air flow Air flow
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Figure 30: Full Path
As the follower travels around the track in Figure 30, the angle of the blade changes
from α to 90° and back again. Figure 31 shows the blade’s angle for one full rotation. The
solid blue line labeled AoA represents the angle of attack of the blade, or the angle of the
blade with respect to an outside non-rotating coordinate system. The lift angle dashed line
and the drag angle dashed line represent the ideal angle of the blade during the lift phase
and the drag phase respectively. The sloped sections of the AoA show where the blade is
transitioning from one phase to the other, which occurs along the front and the back of the
turbine.
Air flow
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Figure 31: Graph of the angle of attack of the blade through one rotation
4.2.2 Airfoil Design
After completing the analysis described in section 3.3, a table of candidate airfoils
was produced. Explanations of the different result categories were given in section 3.3, and
here, the results are discussed in the context of deciding between the top airfoils. The top
six airfoils (bacj, du86137, e874, giiid, giiig, and naca 64209) were disqualified due to
abnormalities in their results (such as having an artificial peak, or a divide by zero error
resulting in an infinite L/D value). The remaining top 10 airfoils as indicated by the
program are displayed in Table 3.
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Table 3: QFils Top 10 Airfoils
Foil Name Overall Results
Angle Results
Ratio Results
Bucket Results
Deviation Results
e63 42.7 5.4 46.3 39.1 0.97
arad6 42.2 5.7 43.3 41.2 0.32
as5045 42.2 5.7 43.3 41.2 0.32
as5046 42.2 5.7 43.3 41.2 0.32
as5048 42.2 5.7 43.3 41.2 0.32
e62 41.8 6.2 44.8 38.8 0.49
s1091 41.2 5.4 41.7 40.6 1.08
a18sm 41.0 6.1 42.8 39.1 0.23
oaf095 40.5 6.1 42.2 38.8 0.21
ma409sm 40.3 5.6 42.0 38.5 0.21
As the ratio results were relatively close to each other, other factors were taken into
account over the ratio and bucket results. The e63 airfoil was attractive due to its higher
L/D ratio, but it was very thin (with a thickness of only 4.27 percent of its chord length)
and had a very small bucket, meaning any manufacturing defects, or if the wind did not hit
it correctly to achieve an angle of attack of 5.4 it could perform poorly. Out of the
remaining airfoils, oaf095 was chosen. This was due to the fact that it had a very small
deviation, but most importantly it was very thick compared to the others (with a thickness
of 9.48 percent of the chord length) meaning it would be easier to manufacture, and would
be stronger than the other airfoils. The final airfoil was a modification of oaf095, which is
shown in Figure 32. The original oaf095 was smoothed, and the trailing edge was closed.
To close the trailing edge, nineteen different airfoils were generated with varying positions
of initial taper. After looking at the drag polars for the 19 airfoils, the best candidate was
chosen for manufacturing.
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Figure 32: Modified OAF095 airfoil used
4.2.3 Shroud Design
Some shroud designs that were considered included:
1- A cylinder with 2 inlets and 2 outlets
2- A cylinder with 2 inlets and 1 outlet; the thought being that air would curve along
the drag side
3- A cylinder with 2 inlets and 3 outlets in order to released air that gets stuck
4- A cylinder with 2 inlets and walls only on the sides (1 very large outlet)
5- A funnel toward 2 inlets with varying outlet configurations
6- A funnel toward 2 angled inlets with various outlets
7- A funnel with varying angles and lengths toward 2 inlets and 2 outlets
After looking at simple cylindrical shrouds with two inlets and two outlets, and at
the flow fields produced by these type of shrouds, such as the one in Figure 33, it was
decided that a funnel should be added to the inlet to increase the wind velocity inside the
shroud. The flow field produced by one of the funneled designs can be seen in Figure 34.
By adding the funnel, the air velocity contacting the blades can be increased by almost 200
percent from the incident wind velocity.
Once it was decided that a funneled shroud would be most beneficial to the
performance of the turbine, several different models were created (as seen in the
appendix). The sizes and positions of the openings were varied along with the angles and
lengths of the funnel.
To analyze the different shrouds, the computational fluid dynamics package Fluent
was used. Operating conditions were assumed to be air at standard temperature and
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pressure (STP), with an inlet velocity of 2.46𝑚
𝑠. To speed up computation and allow for
more shrouds to be analyzed, some simplifications were made to the model. The model
was assumed to be 2-D, as the blades would not span the entire height of the airflow, so the
vertical boundaries were not of concern. The model was also assumed to be steady state,
and was not modeled with the turbine in the center of it. If each turbine was modeled in a
transient state with moving airfoils, it would not be feasible to analyze the number of
shrouds that needed to be analyzed in the time provided. As the design of the turbine was
not finished by the time that the shroud analysis was started (as necessitated by time
constraints), it was decided to not include a turbine in the middle of the shroud in case that
including an incorrect design could later invalidate some or all of our analysis.
Figure 33: Preliminary Shroud Design
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Figure 34: Funneled Shroud Design
The final shroud used was Shroud #26, as seen in Figure 35. This shroud used two
outlets, with two funneled inlets, one of which (the lift side) was angled.
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Figure 35: Drawing of the final shroud design
58
Figure 36: CFD results for the final shroud design (shroud #26)
Shroud #26 was chosen for a few reasons. Looking at the Fluent analysis for it,
shown in Figure 36, one can see that it provides a good stream for the drag side (it breaks
off towards the end, but the blade is also rotating at that point so it does not make as big of
an impact), and more importantly a good stream for the lift side. As the actual turbine
resides in the middle of the shroud and was not modeled in Fluent, this analysis is not
exact. This design was chosen in hopes that the presence of the turbine will decrease the
interference the drag side stream has on the lift side stream, as seen towards the trailing
end of the lift side stream.
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4.2.4 Final Assembly
After the turbine type, airfoil profile, and shroud design had been determined, the
turbine was then designed for manufacturing and assembly. This design was completed in
Solidworks, and it included a combination of custom parts and stock bearings. The
complete design is shown in Figure 37. This figure, like all of the others in this section, is
shown without the shroud so that the components are visible.
Figure 37: Complete turbine model
The exploded view in Figure 38 shows how the turbine and shaft rotate within the
base. The blades are supported by two x shaped plates above and below, which are welded
onto the shaft. The shaft, x plates, and blades, are supported vertically by a thrust bearing
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between the bottom x plate and the large plate with the cam track in it. They are kept
straight and allowed to rotate due to the two large bearings; one in the cam plate and one
in a support plate welded to the bottom tube of the base frame.
Figure 38: Exploded view of the mounting system
In addition to the rotation of the shaft, the blades also needed to rotate within the x
plates and follow the cam track. The rotation was achieved by placing small cylinders at
the center of the top and bottom of the blade, and placing them in bearings in the x plates.
61
The cylinders were welded on the blade holders and were threaded on the other end so
they could be secured in the bearings with bolts. Thrust bearings were placed between the
blade holders and the x plates to ease rotation and keep the blades at consistent heights.
The cam follower was constructed from the same cylindrical aluminum stock and steel ball
bearings as the components just described. Figure 39 shows how all of these parts fit
together.
Figure 39: Exploded view of the components for blade rotation
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Important dimensions of the components in Figure 39 are shown in the drawing in
Figure 40. The most notable of these are the height of the blades, which was about 15
inches, and the height of the blade holders. About 1 inch of the total 1.2 inch height of the
holders was milled out to contact the blade.
Figure 40: Drawing of parts relating to blade rotation
The entire system, including the base frame, was 26 inches tall and about 26 inches
in diameter. Figure 41 and Figure 42 show these dimensions and others that may be of
interest.
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Figure 41: Profile view of the turbine showing height
Figure 42: Plan view of the turbine with dimensions
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4.2.5 Manufacturing
Since this turbine was much larger than those built by previous MQPs, different
materials and manufacturing methods were used. Most of the manufactured parts were
machined from raw aluminum using CNC machines. One exception to this was the airfoils,
which were the most complicated part to manufacture. Table 4 below details the
manufacturing options considered for the blades. The foam and fiberglass method was
chosen because it was inexpensive and it allowed for a relatively thin and therefore more
efficient blade to be made. The other exception to the machining method was the shroud,
which was constructed from aluminum sheets by the method explained in section 3.4.1.