Pre-Swirl Augmented Vertical Axis Wind Turbine

Spencer BoyajianCharles Pecora

Christopher Sullivan

Advisor: Dr. Zha

Table of Contents

Abstract 2

Objectives 3

Background 3

Significance 7

Design & Study Approaches 8

Results & Analysis 10

Conclusions 20

References 21

Appendix I 22

Appendix II 24

Appendix III 29

1

Abstract

The vertical axis wind turbine (VAWT) has historically fallen short in cost effectiveness and performance to the horizontal axis wind turbine (HAWT). Despite some advantages like compactness and simple installation, vertical axis wind turbines have been abandoned in favor of the higher power output and lower relative cost of horizontal axis turbines. The pre-swirl augmented vertical axis wind turbine concept originally envisioned by Dr. Gecheng Zha has achieved a power coefficient of 35% when large prototypes were fabricated and tested at high wind speeds, proving the design to be comparable to a horizontal axis wind turbine. Thus, it can be seen that the innate compactness, lightweight, and simple installation of the vertical axis wind turbine can be utilized without compromising power.

Stages of analysis, assembly, and testing were performed on the wind turbine to establish proof of concept and determine the base performance of the design. Research on past work with vertical axis wind turbines provided insight as how to increase the efficiency of a VAWT while keeping scalability in mind. Mechanical improvements were made to the design to ensure maximum efficiency and reliability prior to investigating the fluid mechanics involved with the physical prototype. The base efficiency of the turbine was experimentally determined to be 14.16%. Using velocity triangles, the relative wind angle incident on the rotor airfoils was estimated. This information, combined with a computational analysis of the airfoil shape utilized in this design, allowed for the determination and implementation of an optimized blade orientation for the prototype. The experimental results showed a 57.15% increase in power output, and an aerodynamic efficiency of 22.25% with the changed blade angles.

An examination of the viability of materials other than the carbon fiber parts used in the prototype revealed that aluminum 3003 sheets offer a much cheaper design with almost identical performance, the only downside being less durability. However, it is important to note that this lesser durability is still enough to withstand normal turbine operations. In order to examine how this design would compete with turbines currently on the market, a cost analysis was conducted using aluminum 3003 as the primary design material. The cost per watt of power was found to be $8.42. The optimized wind turbine design was determined to have a lower cost per unit power and higher efficiency than similarly sized wind turbines.

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Objectives

The objective for this senior design project was to apply the concept of a pre-swirl augmented vertical axis wind turbine and to improve its economic viability. The design was patented by Dr. Gecheng Zha in 2011, and a second-generation prototype model was fabricated and provided for testing, analysis, and optimization.

The main goal of this project was to use this vertical axis wind turbine design to achieve a cost effective and versatile method of harnessing wind energy. In order to achieve this goal, the turbine’s power output needed to be maximized while simultaneously minimizing the cost of the turbine. The completion of this goal was assessed by comparing the resulting design’s power output and cost per watt to similarly sized wind turbines.

Further analysis was then conducted to investigate the ways in which this design can be scaled to a greater size and resulting power output with similar performance, in addition to determining ways in which cost of production can be cut without significant loss in performance.

Background

Increased awareness of the negative environmental impacts of non-renewable energy sources has lead to an increased demand for renewable energy technologies. Wind energy is renewable and essentially infinite source of energy. Unfortunately, the energy available varies with the wind speed. Vertical axis wind turbines have great potential due to their simple and compact design. Currently, the relatively low efficiency and energy output per unit of power of vertical axis wind turbines makes them unattractive as an energy option because they take longer to pay for themselves. However, they can be easily placed on top of existing structures minimizing installation costs. This design project will focus on a newly patented design that is a Darrieus type VAWT.

Figure [1] The three types of VAWTs [1]

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Previous work:

As of late 2012, Sandia National Laboratories is undertaking a project to test the feasibility of vertical-axis wind turbine architecture for large-scale deployment in the offshore environment. This idea is currently being tested at Sandia National Laboratories in New Mexico. The goal is to reduce the biggest barrier to offshore wind development—high cost of energy (COE)—by 20% or more through the application of VAWT rotor technology. The research project will:

Develop innovative VAWT rotor designs that result in cost-effective and easily manufactured rotors for deep-water offshore machines

Demonstrate the potential for greater than 20% reduction in COE for deep-water, floating VAWT systems

Develop specialized manufacturing techniques, certification test methods, and a commercialization plan for offshore VAWT rotors

Test, in a wind tunnel and combined wind-wave tank, a proof-of-concept subscale, deep-water floating offshore wind-turbine generator employing a VAWT rotor [2]

The Department of Mechanical Engineering at Dalhousie University had a project in 2005 on VAWT with concentration on the issue of some VAWTs not being self-starting. Meaning the turbine must be brought to a certain operational speed before it will capture enough wind energy to rotate on its own. Their project involves varying the pitch of the blades (passively and actively) but due to increased complexity, the failure rate, maintenance required, and parts required became cumbersome. Since 2005, self-starting wind turbines have been developed with simpler ideas but again efficiency suffers. This publication is useful for deciding what methods of improvement are worth researching. The publication's results indicate that the benefits of active blade pitch control are negated by high failure rates, maintenance requirements, and overall cost of production, thus indicating that a fixed-blade approach is more appropriate for this design.

The most useful information for our design optimization comes from the WPS International Report written by Dr. Zha [3].  This paper includes information regarding number of blades, both stator and rotor, and their effects on the power coefficient for this turbine style. The wind tunnel testing and analysis that followed indicated that a lower number of larger rotor blades could yield higher efficiencies. In addition, this paper serves as a proof of concept for this stator blade design. Furthermore, it has information regarding the flow interaction with the turbine and where losses are most apparent. For example, the stator blade angles were very high in their initial tests and were found to be too large with respect to the inner blades. Our design will explore and test the effect of a higher rotor chord to stator chord ratio and a decreasing number of internal blades. The CFD work detailed in this paper showcases the high loss areas of the turbine, the center and the rotor blades on return to the front of the turbine. This previous design uses a

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center rotor arrangement where the chords of the blades are perpendicular to the tangential velocity direction. The current design implements CFD research on this angle to optimize the inner blade angle, vastly improving efficiency.    

Past work was also conducted on the rotor design and scalability of VAWTs as part of a student's Master's thesis at Delft University. Information about rotor design and optimization from this publication was used extensively in this project, as data on VAWT became very sparse after research dropped off in the 1980s [4].

Constraints:

1 Economic: The VAWT market has a wide range of turbine designs but it is important to remember that for a design to be useful it has to produce enough power to make the initial investment worth it. This is a hard thing to quantify, but by using existing examples of wind energy systems, it can be determined whether or not this design can compete. In the renewable energy business, the success of the product is a function of how quickly the system can pay off the initial investment. Solar energy, for example, can take up to 10 years to pay off the overhead costs. Increasing the power output of this turbine design will make it more attractive to consumers. However, for military applications, the use of more expensive materials such as carbon fiber to reduce factors such as weight and the radar signature, but will increase these costs. The average cost per kW in wind turbines under 100kW is roughly $3000-$8000 per kilowatt of capacity [5]. Therefore, this turbine must be competitive with these prices in order to be considered practical. Keeping the maintenance costs down is also essential to keeping the design competitive. The initial fabrication and installation of the turbine are the main costs associated with this design.

2 Environmental:  The VAWT poses little environmental impact, as its purpose is to produce clean renewable energy. The materials used in its construction are not hazardous to the environment and its main application would be in locations where horizontal axis wind turbines are impractical, such as the roofs of buildings, on top of skyscrapers, and above other small structures.

3 Social Impact:  There are few social constraints on VAWTs as they are generally accepted as a popular alternative to fossil fuels. Although there is some aversion to large wind energy systems due to their size, noise, and visual disturbance, this design is more compact and versatile, being able to utilize spaces otherwise wasted such as the roofs of tall buildings. These areas are out of sight and should not produce any social impacts.

4 Political:  This project has relevant political constraints, most of which can be seen in a positive light. For example, renewable energy systems are subsidized such that a percentage of their initial cost can be refunded via tax deductions. This makes entering the market easier as the cost of a wind turbine can be subsidized, making it a more attractive option for the consumer. This may change in the future as renewable energy systems become cheaper and the subsidization decreases.

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5 Ethical:  Ethical constraints will not affect this design.

6 Health and Safety:  The safety constraints of this design include design codes and standards for the materials used in the design. Safety issues regarding materials must be taken into account to ensure that the product will be operating with high enough safety factors to prevent failure. Additionally, a problem wind turbines have is bird kills, which occur when birds cannot see the path of the spinning blades of wind turbines and the turbine strikes them. This is a problem for horizontal axis wind turbines, but because this design utilizes stator blades that surround and clearly define the swept area of the rotor blades, it is unlikely that birds will fly into the kill zone.

7 Manufacturability:  This design is subject to manufacturability constraints as it uses many unique parts, such as the custom high-camber airfoils and the plates to which they attach. Carbon fiber is very tricky to implement in a design due to the high risk of brittle fracture at attachment points. Using aluminum can help keep costs low, as using sheets to mold the airfoil shapes is a less expensive process than fabricating a composite material. For military applications, the use of carbon fiber in the design may introduce more difficulty in manufacturing but, by using one mold each for the stator and turbine blades, the feasibility of manufacturing remains optimal. An aluminum design eliminates the need for fasteners, as the sheets will have fold-over tab and slot joints. By using Aluminum 3003, the favorable ductility needed for bending the sheets around the airfoil profiles is retained. This type of aluminum still has favorable erosion resistance properties even before the application of the 3M™ Wind Protection Tape. 

8 Sustainability:  Our design is not affected by sustainability constraints, as wind turbines do not produce harmful by-products.

9 Codes and Standards:  In Miami-Dade County there are no specifications for renewable energy systems such as wind turbines and, therefore, all building codes and regulations apply. The codes affecting this design can be found in the “Miami-Dade Sustainable Development and Building Code: Project Code Diagnosis Report and Priority Recommendations” [6]. “Standards for Wind Energy Systems in Urban/Suburban Areas” also contains details specific to building wind energy systems that apply to this design [7]. Some of these constraints include zoning regulations, noise regulations, height parameters, electrical codes, and turbine appearance codes. This design falls well within the size constraints and noise constraints set forth and the remaining electrical codes rely upon where this turbine will be implemented. The turbine appearance requirements are met as well utilizing the 3M™ Wind Protection Tape, with these requirements being that the blades are a neutral color (gray satisfies this clause).  

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Significance

Improving VAWT technology allows us to make another step closer to breaking dependence on fossil fuels. This project proves the pre-swirl concept is a great method to increase efficiency in Darrieus type VAWTs utilizing high cambered airfoils as blades. Additionally, it provides insight into how the angle of attack of the blades with respect to the radial direction affects performance. Finally, this project leaves a path open for further research and progress in the relatively unexplored field of vertical axis wind turbines.

Vertical axis wind turbines are generally less expensive to manufacture and more versatile than the wind turbine axis turbine. For these reasons, the style of turbine should be more widespread than it is; however, it is hindered by the low efficiencies of common designs. Typical vertical axis wind turbine efficiencies are around 8-10% with well optimized designs around 15%, while for horizontal axis wind turbines efficiencies are roughly 35%. According to a paper recently published by Dr. Zha, the pre-swirl augmented vertical axis wind turbine achieved 35% energy efficiency in preliminary testing. This turbine design is expected to have 20-40% higher power output than the best vertical axis wind turbines on the market [7]. This pre-swirl design shows promise and with further research could lead to great advancement in the stale vertical axis wind turbine market.

If this sort of power output is achieved and the design is made to be cost competitive with similar horizontal axis wind turbines, then the significance of this project would be great. A vertical axis wind turbine is versatile, as it can easily be installed without high poles or masts for elevation. It can also be installed on rooftops and in tight quarters. Its footprint when viewed from above is only a circle versus the footprint a horizontal axis turbine makes, the diameter of the turbine as a whole. For this reason, this design could make wind energy more attainable in urban environments and on smaller scales than the vast wind farms in the countryside. The company working with Dr. Zha on this design previously had hoped to market the turbine to the Department of Defense. For this reason, they have high interest in increasing the efficiency of the turbine to increase the amount of power the turbine is capable of producing.

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Design and Study Approaches

Figure [2] Preliminary design assembly and cross section

The figure above shows the preliminary design for the vertical axis wind turbine with the number of outer stators blades installed varying. The eight small blades around the outside of the turbine are the stator blades. These redirect the flow to maximize the amount of energy that can be absorbed from the wind. The rotor blades are the three internal blades. The specifications for the blades and their airfoils are listed in Table [1]. The orientation angle listed refers to the angle between the radial direction in the turbine and the cord of the airfoil.

Cord Length (mm)Thickness (%) Camber (%) Orientation (°)

Stator 105 20 15 30Rotor 218 20 26 6

Table [1] Given Airfoil Specifications

The airfoils are arranged in the manner shown in Figure [1], resulting in a design with a frontal rectangular cross section. The height of the turbine used for testing is 0.762 meters and the outermost diameter of the turbine is 0.662 m. This gives the turbine a cross section of 0.504 m2.

The prototype model provided for testing and optimization was made using a woven, unfinished carbon fiber for blade construction. Although light, the cost of manufacturing can be quite high. The low weight, and thus moment of inertia should allow for a reduced starting wind speed. The prototype shaft used for driving the

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generator is made of aluminum 6061-T6. The generator itself is a 200-watt low-torque 3-phase generator that was provided by Dr. Zha specifically for the testing of the turbine prototype. The generator is hooked up to a rectifier setup that was wired in order to test the power output through a dummy load. Resistors ranging from 0.47 Ohms to 200 Ohms were used.

The original prototype came with bearings, but these were found to be far too inefficient for use with this design. Because of this, bearings designed for use with low rpm, light load capability, and a sealed bearing chamber for outdoor use were required. The ReliaMark UCF205-16 RM Ball Flange Unit Bearings were selected to replace the old bearings. These replacements have a lower load capacity, but this translates into a lower force required to spin the bearing. A smaller force required to spin the bearings also means a lower cut-in wind speed and less rotational drag for the turbine. The turbine was dismantled and bearings replaced. Unfortunately, due to funding issues only metal-housed bearings could be acquired, as opposed to the thermoplastic housed-bearings included in the original design to reduce radar signature in military applications.

When wind-tunnel testing for this turbine, a number of measurements were taken. Because the turbine could not fit in the small test chamber of the wind tunnel, the turbine was placed in the exhaust flow section of the tunnel, where wind speed varied substantially. It was therefore imperative that accurate wind speed measurements were conducted for each wind tunnel fan frequency at which the prototype turbine was tested, in order to accurately calculate wind energy. Wind energy can be determined as shown in Equation [1] using wind speed Vw, air density ρ, and cross-sectional area A.

Wind Energy=1/2∗ρ∗A ¿V w3 [1]

The power output of the wind turbine was the main conern of this project, and it was therefore essential to develop a method to precisely and accurately determine the turbine’s power output. To do this, the DC voltage across a dummy load was measured using a multi-meter. The electrical power output was then calculated using the relationship shown in Equation [2], where P is power, V is voltage, and R is resistance. Further, efficiency was found from the ratio of electrical power output and the wind energy.

P=V 2/R [2]

Despite some positive evidence from preliminary testing done by Dr. Zha, the first test for this design was to determine whether the pre-swirl design was effective at all in increasing the wind turbine efficiency. Initial tests examined the power output and efficiency of the turbine with all eight stator blades. Four stator blades were then removed, and the test repeated. Finally, the front blade was taken off, leaving three blades on the side of our turbine facing away from the incoming wind. It was believed that this arrangement would satisfy an effective “no-stator” setup, thus performing similarly to the turbine with no stator blades at all. These efficiencies were compared to

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determine whether including stator airfoils increases power enough to compensate for the added cross-sectional area.

Once the number of stator blades to be included was determined, the next goal was to optimize the rotor blades. In order to produce the most power from our turbine, the lift on the rotor airfoils was examined. First, the relative wind speed and angle of attack to the inner airfoils had to be determined. From the geometry of the stator airfoils, it was approximated that the wind enters the turbine at a 60° angle relative to the radial direction. The wind speed and rotational speed of the rotor blades were measured in the wind tunnel and these numbers were used in a velocity triangle to determine the relative wind speed of the rotor blades.

ANSYS Fluent was used to determine the desired angle of attack of for the high-camber rotor airfoil shape. The standalone shape was used in the program with a range of angles of attack, from -5° to 45°. The results obtained from ANSYS included the forces on the airfoil in the x and y directions.

In order to maximize power output, the force on the airfoil in the direction of rotation was to be optimized. To calculate this tangential force, the orientation of the airfoil had to be determined for each angle of attack using the relative wind velocity calculated from the velocity triangle. Once the orientation of the blade was determined, the x and y components of force were converted into a single value for tangential force. The optimal angle of attack was then determined from the greatest tangential force value.

This optimal angle of attack was then used to guide our repositioning of the rotor airfoils. Once the blades were adjusted, more testing was done to determine the change in power output. As this calculation relies heavily on experimental data from testing under specific conditions, this testing and simulation procedure can be repeated in order to optimize the turbine for any wind speed.

Results & Analysis

Upon receiving the preliminary wind turbine prototype, the severe resistance when spinning the rotor blades was apparent. Tests were run before and after replacing the excessively lubricated bearings. Results from the testing are shown in Table [2]. The testing was conducted at a wind speed of 2.612 meters per second in both cases with eight stator blades and the original rotor blade orientation, which was a 6.5° inclination. The change of bearings resulted in a 165% increase in both power output and efficiency.

Old Bearings New BearingsTurbine Power (W) 0.258 0.684Efficiency 4.69% 12.43%

Table [2] Turbine power and efficiency from bearing change

After determining the baseline efficiency from the preliminary design and the new bearings, testing was done with zero, four, and eight stator blades and the original rotor

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orientation. Due to the decreased structural integrity with reduced number of blades, the wind speed was only set to 2.612 meters per second for testing.

Number of Stators 0 4 8Turbine Power (W) 0.001 0.174 0.684Efficiency 0.02% 3.16% 12.43%

Table [3] Turbine Power and Efficiency for varied number of stator blades

The results from this table indicate that the inclusion of stator airfoils in this design is beneficial to the efficiency. The removal of stator blades from the turbine resulted a 99.84% decrease in efficiency when compared with the eight-stator blade configuration. The four-blade arrangement resulted in a 74.59% decrease in efficiency. The fact that the no blade arrangement fared so poorly is not surprising considering that the rotor airfoils are shaped and oriented in a way that is meant to capture energy from the wind after it has been swirled. From this testing, it was determined that an eight-blade configuration would be the most efficient for our vertical axis wind turbine design.

Once the pre-swirl concept was experimentally proven to increase efficiency, the next aim was to optimize the power output using aerodynamic analysis. In order to understand the relative wind speed to the rotor blades, the wind speed, wind direction, and rotational speed of the blades was measured. These measurements are in Table [4]. Also, Figure [3] depicts a representation of the velocity triangle and vector addition.

V wind Wind Angle Rotor speed V relative Relative AngleLeading Edge 3.38 m/s 60° 4.59 m/s 2.37 m/s -44.9°Trailing Edge 3.38 m/s 60° 1.22 m/s 2.40 m/s 45.22°

Table [4] Relative wind speed and angle calculations for base design

Figure [3] Velocity triangle for relative wind speed to rotor blade

The results shown in Table [4] suggest that there is a variable angle of attack along the length of the rotor airfoils. The leading edge was found to have a negative relative wind angle and the trailing edge a nearly equal and opposite relative wind angle.

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This is due to the fact that the leading edge rotates faster than the trailing edge. This result was used to estimate that the mean relative wind angle is roughly 0°. Using this information, we conducted analysis assuming that the relative wind incident on the rotor blades travels along the radial direction.

With this information, flow over the rotor airfoil shape was simulated using ANSYS Fluent. Simulations were done with a straight flow of 5 meters per second wind speed at varied angles of attack, shown in Figure [4]. In the figure, the net tangential force is plotted against the angle of attack. The net tangential force was calculated in the direction of rotation from the x and y components of force, which were obtained from the output of the Fluent simulation. The orange data point indicates the preliminary angle of attack data point, and the green data point indicates the ideal angle of attack.

-10 0 10 20 30 40 500

2

4

6

8

10

12

14

16

Angle of Attack (degrees)

Net

Tan

gien

tial

For

ce(N

)

Figure [4] Plot of net tangential force versus angle of attack

Figure [5] shows a contour plot of the static pressure around the airfoil obtained at the ideal angle of attack of 25°. Using this optimized angle of attack, it was determined that the power coefficient of the turbine could be increased by rotating the rotor airfoils. New holes were drilled to align the airfoils at roughly a 25° inclination from the radial direction. Based on the relative velocity calculations, this would allow for a 25° angle of attack and a maximized power output.

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Figure [5] Contour plot of static pressure with a 25° angle of attack and 5 m/s wind speed

The optimized blade orientation was then tested in the same conditions as the preliminary design was tested, with a 3.383 meters per second wind speed. The comparison of power output and efficiency is shown in Table [5].

Rotor Blade Angle 6° 25°Turbine Power (W) 1.693 2.660Efficiency 14.16% 22.25%

Table [5] Turbine power data before and after optimized blade orientation

Results from Table [5] indicate the success of the rotor blade angle optimization. The change resulted in a 57.15% increase in both power and efficiency. Figure [6], below, shows the change in blade angle from the preliminary design to the optimized design. The inner rotor blades were rotated 19°.

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Figure [6] Preliminary 6° orientation (left) and optimized 25° orientation (right)

The final design utilizes two airfoil shapes in the configuration shown above on the right. The specifications of the two airfoils along with their orientations are specified below in Table [6].

BladeCord Length Thickness Camber Orientation

Outer Radius

Blade Length

Stator 0.105 m 20% 15% 30° .381 m 0.742 mRotor 0.218 m 20% 26% 25° .280 m 0.712 m

Table [6] Rotor and stator blade dimensions and positions

Figure [6] Stator (left) and Rotor (right) blade models

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Figure [6] provides a view of the models of both the stator and rotor blades created using the dimensions and specifications presented in Table [6]. The differences in camber of the airfoils is clearly depicted in the figure.

Figure [7] Rotor (left) and Stator (right) baseplate models

The baseplate models of the stator and rotor assemblies are shown in Figure [7]. Two baseplates are required for each set of blades, one oriented above the blades and one below, in order to provide structural support as well as an attachment point between the upper and lower shafts and the turbine’s bearings.

Figure [8] Upper and lower shafts, respectively

Figure [8] provides models of the upper and lower shafts which, when inserted into the turbine’s bearings attached to the stator baseplates, allow for the rotation of the inner rotor blades with respect to the stationary ring of stator blades.

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Figure [9] Outer assembly

The model shown in Figure [9] is that of the outer assembly, formed by eight stator blades and two stator baseplates. The bearings of the turbine are fixed on the outer faces of the baseplates, concentric with the holes at the center of the baseplates.

Figure [10] Inner assembly

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Figure [10] depicts a model of the inner assembly of the turbine design, consisting of three rotor airfoils, two rotor baseplates, and the upper and lower shafts. This assembly fits concentrically inside of the outer assembly shown in Figure [9].

Figure [11] Complete assembly

Figure [11] provides an isometric view of the complete assembly. As can be seen, the rotor assembly is in place within the stator assembly, with the upper and lower shafts in their proper locations for smooth rotation within the bearings.

Figure [12] Connection shaft

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Figure [12] contains a model of the connection shaft that was designed and fabricated to transfer motion from the lower shaft of turbine to the generator centered under the turbine. As can be seen, one side of the shaft utilizes a hex-shaped male head in order to fit into the corresponding female connector required by the generator. The other end of the shaft was fabricated into a D-shape connector in order to be properly fitted to the turbine’s lower shaft.

(Note: Detailed drawings of each design component, along with specifications for material type, dimensions, and resulting weights, can be found in the Appendix III.)

The important quantity that was calculated during this design and testing was the aerodynamic efficiency of the turbine. This value can generally be used to determine the quality of a turbine design. While 22.25% efficiency is quite impressive for a vertical axis wind turbine design, it is important to note that the wind used during testing was the exhaust section of a wind tunnel rather than the test section. For this reason, the wind speed measurements were not uniform and contained high variance. Table [7] below shows the error analysis and a 95% confidence interval for the turbine power output, the wind energy, and the efficiency calculations. It is important to note that this error analysis reflects that despite the high variation wind energy, and thus aerodynamic efficiency, the power output was accurately measured. This suggests that the results reflecting the change in power and efficiency between designs are meaningful, although more accurate testing is required to obtain a reliable value for efficiency.

Power Output (W) Wind Energy (W) EfficiencyMean 2.660 11.959 22.25%Standard Error 0.064 3.032 5.67%

95% Confidence 2.524 5.530 10.23%2.797 18.387 34.26%

Table [7] 95% confidence interval for turbine power output and efficiency

To properly gauge how our turbine competes with the rest of the wind energy market we have calculated an estimated cost for our design utilizing cheaper aluminum construction versus the military-needed specific carbon fiber design. This drives down the cost of manufacturing significantly and reveals how this design is indeed a competitive option for wind energy.

Based on the availability of raw 1/8”, 4x10ft aluminum 3003 sheets priced at $227.62 per sheet, it was determined that the total cost requirement for the 47 square feet needed for the design is $267.45 [10]. Only one sheet is required with minimal extra material. The ¾” aluminum 6061 shaft was obtained and cut to length at C&R Metals for $7. The metal work for the blades and the end plates can be sourced to Doudney Sheet Metal Works’ south Miami location. A verbal estimate was given for manufacturing cost of $15 for the end plate stamping, and a further $70 to have all of the airfoil shapes manufactured. The two ReliaMark UCF205-16 RM Ball Flange Unit bearings were obtained from Florida Bearings Miami, a Kaman company, for $64.38. The generator is a Permanent Magnet Generator for a Wind Turbine rated for 200W. It can be obtained

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directly from the company website for $249 [11]. A ten-piece set of Uxcell M10x20mm Thread 304 Stainless Steel Hex Socket Bolts and associated ten-piece set of M10x1.5mm 304 Stainless Steel Nylock Nylon Insert Hex Lock Nuts, both of which are required for assembly of the turbine, can be acquired for $8.05 and $7.70, respectively. Finally, to satisfy aforementioned code restrictions, the turbine must have a neutral gray color. 3M manufactures a wind protection tape specially designed for wind turbine blades and offers great performance and erosion prevention [12]. This product is available by special order only and ranges in price with the average cost for the protection tape required being $30 (See Appendix I for full commercial pricing information and calculations used in determining material costs).

Item/Service Price1/8" Aluminum 3003 Sheet, 47 ft^2 $267.453/4" Aluminum 6061 Shaft $7Metal Bending/Cuts $85Bearings $64.38Generator, 200W $249Wind Protection Tape $30Hex Socket Bolts $8.05Hex Lock Nuts $7.70Total Cost: $718.58

Table [8] Price list of materials and manufacturing

As can be seen in Table [8], the total manufacturing cost of the wind turbine is $718.58. Placing the turbine at a market price of $1000 results in a gross profit margin of 28.14%. Table [9] provides further cost analysis by comparing this turbine design to other turbines of similar size. Data for both a 100-Watt horizontal axis wind turbine made by MOLA Energy Technology Co. [8] and a 100-Watt vertical axis wind turbine made by Qindao Bofeng Wind Power Generator Co. [9] are used for comparison. These turbines were chosen for their comparable dimensions to our design, as cost per watt of a turbine decreases substantially when a design is scaled up. The power output listed for the project design is an estimate based on the experimentally obtained efficiency, as we were unable to test above 3.383 meters per second.

Project Design Competing HAWT Competing VAWTSwept Area (m^2) 0.5044 0.8659 0.6400Wind Speed (m/s) 12 12 12Wind Energy (W) 533.86 916.47 677.376Turbine Power (W) 118.76 100 108Turbine Efficiency 22.25% 10.91% 15.94%Cost $1000.00 $1,000.00 $1,000.00Cost per Watt $8.42 $10.00 $9.26

Table [9] Power and cost comparison with existing small wind turbines [8] [9]

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The comparison shown in Table [9] implies that the project design turbine is capable of producing more power than existing wind turbines at a lower cost per watt and a smaller swept area.

Conclusions

Evidence that the inclusion of stator pre-swirl blades in a vertical axis wind turbine design increases efficiency was obtained experimentally, and further optimization was performed using fluid mechanics principles and computational analysis. After optimization, the turbine’s power output and efficiency were increased by 57.15% when compared to those of the base model. It was also determined that the aerodynamic efficiency of the optimized wind turbine design was 22.25%, which suggests that the turbine could outperform similarly sized existing wind turbines currently on the market, both in efficiency and cost per unit power ($8.42 per watt).

This project has given new insights on vertical axis wind turbines and could potentially lead to further improvements in this field. Future work can be done to improve the results of this project. Perhaps most importantly, the reliability of testing can be improved by using a wind tunnel with a test section that is large enough to house the entire turbine, thus providing sustained, evenly distributed wind speeds. This would likely lead to more accurate efficiency calculations and better overall performance. This would also allow for testing at higher wind speeds, whereas current results were hindered by wind tunnel limitations.

Furthermore, the testing and optimization methods used in this project can be replicated for a similarly designed wind turbine of any size and any wind speed. A larger wind turbine that utilizes the same pre-swirl concept can be optimized for high wind speeds. In scaling up, the cost per unit power could be lowered and the cost effectiveness of this wind turbine concept could be further improved.

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References

[1] "Wind Energy Overview," Belarusian web portal on renewable energy, http://re.energybel.by/en/renewable-energy-technologies/wind/

[2] Sutherland, H.J., Berg, D.E., and Ashwill, T.D., “A Retrospective of VAWT Technology,” Sandia National Laboratories Technical Report, SAND2012-0304, January 2012.

[3] Zha, Gecheng, A Novel Concept of Pre-Swirled Augmented Vertical Axis Wind Turbine, WPS International Report, June 30, 2015.

[4] M. Schelbergen B., "Structural Optimization of Multi-Megawatt, Offshore Vertical Axis Wind Turbine Rotors. Identifying Structural Design Drivers and Scaling up of Vertical Axis Wind Turbine Rotors", 2013, Delft University

[5] "How Much do Wind Turbines Cost?" Windustry.org http://www.windustry.org/how_much_do_wind_turbines_cost

[6] "Miami-Dade Sustainable Development and Building Code Project. Code Diagnosis Report and Priority Recommendations", Clarion Associates, August 2011.

[7] "Standards for Wind Energy Systems in Urban/Suburban Areas", Municipal Code, 2011.

[8] "H-100W Direct Drive Permanent Magnetic Wind Turbine 2," http://qdbofeng.en.alibaba.com/product/284869947-209790256/H_100W_Direct_Drive_Permanent_Magnetic_Wind_Turbine_2.html

[9] "Hot selling Portable Easy To Install Mini HAWT 50W 100w diy wind power generator," http://www.alibaba.com/product-detail/Hot-selling-Portable-Easy-To-Install_60173084022.html?spm=a2700.7724838.0.0.DJiRHo

[10] Aluminum 3003 Sheet, Cut 2 Size Metalshttp://www.cut2sizemetals.com/aluminum/sheet/ash/?_kk=aluminum%20sheeting&_kt=cb7e6ba6-57b6-4b37-8406-db6a5a0b1107&gclid=CjwKEAjw_7y4BRDykp3Hjqyt_y0SJACome3Tkl5_U17obhyaRCbyoRc7oQwMmPWnFUKYdBXUqbXimhoC8Ffw_wcB

[11] Permanent Magnet Generator for Wind Turbine 200Whttp://small-generator.com/buy/index.php?main_page=product_info&cPath=1&products_id=42

[12] 3M™ Wind Protection Tapehttp://solutions.3m.com/wps/portal/3M/en_US/Wind/Energy/Products/Wind_Protection_Tapes/

21

Appendix I

Materials and fabrication costs

1/8” thick 4x10ft aluminum 3003 sheet, $227.62.http://www.cut2sizemetals.com/aluminum/sheet/ash/?_kk=aluminum%20sheeting&_kt=cb7e6ba6-57b6-4b37-8406-db6a5a0b1107&gclid=CjwKEAjw_7y4BRDykp3Hjqyt_y0SJACome3Tkl5_U17obhyaRCbyoRc7oQwMmPWnFUKYdBXUqbXimhoC8Ffw_wcB

Aluminum Cost CalculationsComponent (#) stator (8) rotator (3) disk 1 (2) disk 2 (2)Surface Area (single) 0.18 0.38 0.3136 0.5776Surface Area (total) 1.44 1.14 0.6272 1.1552

sum: 4.3624 m^246.96 ft^2

Rate: $227.62 40 ft^2Final Cost: $267.45 47 ft^2

Aluminum 3/4" shaft cut to length $7C&R Metals2991 NW North River Dr, Miami, FL 33142

Metal bending and cuts/stamps performed at Doudney Sheet Metal Works’ South Miami location. 3020 S.W. 38th Ave. Miami, FL 33146Verbal estimate from Adam of $85.00 ($15 for end plates stamped, $70 for airfoils).

ReliaMark UCF205-16 RM Ball Flange Unit2X$32.19=64.38Florida Bearings Miami (a Kaman company)10050 NW 116th Way, Ste 1Miami, FL 33178

Permanent Magnet Generator for Wind Turbine 200W. $249.00Listed on http://small-generator.com/buy/index.php?main_page=product_info&cPath=1&products_id=42Model: YAF-200Rated power: 200WMax power: 220WRated voltage: 12/24VMax start resisting torque: 0.35N.MRated speed: 450r/m

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Max speed: 500r/mType: Three-phase permanent magnet generatorWorking temperature: -40℃-80℃Protection: IP54Net weight: 3.0kg

3M™ Wind Protection tape, ~$30. Special order only.available at http://solutions.3m.com/wps/portal/3M/en_US/Wind/Energy/Products/Wind_Protection_Tapes/Product number: W8640Color: GrayThickness: 0.38mmTensile Strength @ Break lb/in (N/100 mm): 87 (1542)Elongation at Break (%): 500Service temperature: -40 to 200 degrees Fahrenheit

Item/Service Price1/8" Aluminum 3003 Sheet, 47 ft^2 $267.453/4" Aluminum 6061 Shaft $7Metal Bending/Cuts $85Bearings $64.38Generator, 200W $249Wind Protection Tape $30Hex Socket Bolts $8.05Hex Lock Nuts $7.70Total Cost: $718.58

23

Appendix II

Excel Calculations

ConstantsLoad (Ohms) 0.47rho (kg/m^3) 1.225Area (m^2) 0.5044No Stator Area (m^2 0.38862

Wind Speed Measurements (m/s)30Hz 35Hz

1 1.57 2.892 2.01 3.063 2.89 2.184 1.05 4.35 1.46 3.066 3.24 3.947 2.89 2.688 3.42 2.369 3.42 5

10 2.54 3.0611 4.24 4.68

mean 2.612 3.383SD 0.297 0.286

Pre-Bearing Change

Old Bearings New BearingsVoltage (V) 0.348333333 0.567Wind Energy (W) 5.504400092 5.504400092Turbine Power (W) 0.258161939 0.684019149Efficiency 4.69% 12.43%

Voltage Measurements (V)

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Blade Arrangment 0 4 (6°) 4 (6°) 8 (6°) 8 (6°) 8 (25°)Tunnel Frequency (Hz) 30 30 35 30 35 35

1 0.0143 0.292 0.552 0.561 0.901 1.1242 0.0136 0.258 0.586 0.578 0.904 1.0983 0.0198 0.333 0.518 0.569 0.887 1.1274 0.0238 0.271 0.534 0.559 0.875 1.1315 0.0285 0.275 0.551 0.566 0.895 1.111

mean 0.020 0.286 0.548 0.567 0.892 1.118SD 0.006 0.029 0.025 0.008 0.012 0.014

Blade Arrangment 0 4 (6°) 4 (6°) 8 (6°) 8 (6°) 8 (25°)Tunnel Frequency (Hz) 30 30 35 30 35 35Wind Speed (m/s) 2.612 2.612 3.383 2.612 3.383 3.383Voltage (V) 0.02 0.2858 0.5482 0.567 0.892 1.1182Wind Energy (W) 4.241 5.504 11.959 5.504 11.959 11.959Turbine Power (W) 0.001 0.174 0.639 0.684 1.693 2.660Efficiency 0.02% 3.16% 5.35% 12.43% 14.16% 22.25%

CFD Analysis5 m/s wind speedAngle (deg) Vwindx (m/s) Vwindy (m/s) Fy (N) Fx (N)

-35 0.819152044 -0.573576436 6.6772367 4.8291441-30 0.866025404 -0.5 8.4859605 5.1302931-25 0.906307787 -0.422618262 10.550234 5.1790353-20 0.939692621 -0.342020143 12.288527 4.7787545-15 0.965925826 -0.258819045 13.438554 3.9717039-10 0.984807753 -0.173648178 13.989815 2.9108142

-5 0.996194698 -0.087155743 14.168544 1.78774310 1 0 14.260908 0.599991925 0.996194698 0.087155743 13.022937 -0.30507365

10 0.984807753 0.173648178 11.364019 -0.9090585815 0.965925826 0.258819045 9.9562366 -1.2077993

Angle (deg) Actual Angle Angle to Radial Normal Force

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of Attack Direction from x-35 -5 -35 8.239555357-30 0 -30 9.914203919-25 5 -25 11.75051413 Original-20 10 -20 13.18186844-15 15 -15 14.00859899-10 20 -10 14.28273586 Optimal

-5 25 -5 14.27044049 Optimal0 30 0 14.260908 Optimal5 35 5 12.99996971

10 40 10 11.3492303815 45 15 9.929587526

Our Design Competing HAWT Competing VAWTSwept Area (m^2) 0.5044 0.8659 0.6400Wind Speed (m/s) 12 12 12Wind Energy (W) 533.86 916.47 677.376Turbine Power (W) 118.76 100 108Turbine Efficiency 22.25% 10.91% 15.94%Cost $995.00 $1,000.00 $1,000.00Cost per Watt $8.38 $10.00 $9.26

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Appendix III

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