Energy Ambassador.pdf

7/27/2019 Energy Ambassador.pdf

1/20

Dalhousie University

Mechanical Engineering

Final Year Design Project

Self-Starting Vertical Axis Wind Turbine

Group MembersJon DeCoste

Denise McKayBrian Robinson

Shaun WhiteheadStephen Wright

SupervisorsDr. Murat Koksal

Dr. Larry Hughes

January 16, 2006


2/20

i

EXECUTIVE SUMMARY

With the recent surge in fossil fuel prices, demands for cleaner energy sources, andgovernment funding incentives, wind turbines have become a viable technology for

power generation. In January 2006, Canadas wind power capacity reached 682 MW [2],

and it has been suggested that Canada has the wind resources capable of supplying 20%of Canadas power requirements, translating to 50 000 MW of wind power capacity [2].

Northern Quebec alone has the wind resources to supply 40% of Canadas electricity

requirements [2]. On a larger scale, the global wind power capacity at the end of 2004was more than 47 000 MW, with Europe supplying 72% of the total capacity [3].

Denmark is a world leader in wind energy production, having a capacity of 3542 MW,

from both off and onshore turbines in January 2005 [4], which leads to 20% of

Denmarks electricity being supplied by the wind [5].

These statistics suggest that Canada has the potential for a substantial increase in wind

power capacity. In 2001, Natural Resources Canada introduced a wind power production

incentive (WPPI) in an effort to increase Canadas wind energy production. The WPPIprovides support for 1000 MW of new wind energy capacity installed from 2001 to 2006

[6]. Another advantage of increasing Canadas wind power capacity is the decreasedamounts of greenhouse gas emissions. With Canadas commitment to the Kyoto Protocol,

the country is responsible for reducing greenhouse gas emissions by 6% of the 1990

levels between the years 2008 and 2012 [7]. In an effort to meet the conditions set out by

the Kyoto Protocol, Canada is in a position to gain tremendously from increasing windpower capacity to levels approaching those seen in European countries such as Denmark.

Currently, horizontal axis wind turbines (HAWT) dominate the wind energy market.However, the power a turbine can produce is proportional to the turbines swept area. As a

result, HAWT designs are continuously getting bigger to produce more power, whichmeans that the blades must be made continuously larger. Increasing blade size adds extraweight to the blades, leading to higher centrifugal and inertial forces that the blade must

be able to withstand. Also, increased blade size leads to large bending moments on the

blades at high rotational speeds. For these reasons, it has been suggested that HAWTtechnology will likely peak in the next few years [8], making way for the vertical axis

wind turbine (VAWT) design, which allows for increased sizing without the limitations

incurred by the HAWT.

Vertical axis wind turbines have the potential to produce more power than the common

HAWT based on their structural superiority. There is currently research being conducted

in Canada and the United States surrounding VAWT designs, and one Canadian companyis producing a Darrius turbine rated at 250 kW [8]. Other progress made by European

researchers has led to the introduction of a VAWT design that will be rated from 1 to 10

MW [8], being the first of its kind to generate this amount of power. VAWT capacitiesare comparable to HAWT, and with a possible shift in technology from horizontal to

vertical designs, the potential for VAWT to reach a higher capacity than the HAWT are

plausible. Other advantages of the VAWT are that the mechanical power generationequipment can be located at ground level, which makes for easy maintenance. Also,


3/20

ii

VAWT are omni-directional, meaning they do not need to be pointed into the direction of

the wind to produce power.

Although VAWT technology is very promising due its large power production potential,

there are also important hurdles that prevent the full utilization of this technology.

Firstly, boundary layer affects from the ground influence the air stream incident on theVAWT, which in some cases leads to inconsistent wind patterns. Secondly, VAWT are

not self-starting; an outside power source is required to start turbine rotation until a

certain rotational speed is reached.

The main objective of this project is to design and build an H-type, vertical axis wind

turbine which has the capability of self-starting. The prototype will provide a means fortesting various operating and design parameters that affect the turbine performance so

that the VAWT technology can be furthered and the energy conversion efficiency of

these devices can be substantially improved. This report outlines the efforts made

between September and December 2005 in the design of our full-scale VAWT, which is

to be built in January and February, and with further testing planned for March.

The self-starting issues surrounding VAWT will be tackled by the use of alternative bladeprofiles and pitching mechanisms. In the beginning of the project, a mathematical model

was developed that simulates the performance of a VAWT. The model incorporates

several design and operating parameters such as wind speed, overall blade and turbinedimensions as inputs and provides the power that can be produced. Using the model, it

was found that the combination of a chambered blade and a pitching mechanism could

potentially solve the self-starting problem and improve the turbine performance.

Using model and prototype testing results from the Dalhousie Wind Tunnel Facility a

full-scale turbine was designed. The production of the turbine is currently ongoing. Thefull-scale VAWT will be approximately 10ft tall, with a blade height of 5ft, and a

diameter of 8ft. Four sets of blades will be made from wood, while the other components

are primarily made from aluminum for its low weight compared to steel. The finalprototype will be tested rigorously under varying operating conditions and design

parameters such as pitch angle, blade chord length, blade profile and the number of

blades.

It is hoped that the test results obtained from the full scale turbine testing will be used to

further research and education surrounding vertical axis wind turbines, and help to

develop a more efficient turbine technology. This is especially crucial since the amountof information on VAWT is limited compared to conventional HAWT technology even

though VAWT offer significant advantages. We hope to change this with the testing to be

conducted with the full-scale turbine. Not only would the test results fuel furtherresearch, they will also be a key factor in our search for alternative energy sources that do

not harm our environment.


4/20

iii

Table of Contents

Executive Summary ............................................................................................................. i

Glossary..............................................................................................................................iv

1.0 Introduction ............................................................................................................. 11.1 Horizontal versus Vertical Axis Wind Turbines ................................................. 1

1.2 Turbine Technology ............................................................................................ 2

1.3 Wind Power......................................................................................................... 31.4 Wind Energy Applications .................................................................................. 4

2.0 Project Objective ........................................................................................................... 6

3.0 Design Process .............................................................................................................. 83.1 Excel Model .............................................................................................................. 8

3.2 Wind Tunnel Testing................................................................................................. 8

3.3 Full Scale Turbine Design....................................................................................... 10

4.0 Conclusion................................................................................................................... 14

References ......................................................................................................................... 15


5/20

iv

GLOSSARY

Angle of Attack Angle between chord of airfoil and apparent (relative) wind.

Blade Pitch Angle between blade chord and blade direction of travel.

Drag In a wind generator, the force exerted on an object by moving

air. Also refers to a type of wind generator or anemometerdesign that uses cups instead of a blade or airfoil.

H-Rotor A Vertical Axis Wind Turbine design with straight blades

(usually vertical blades).

HAWT Horizontal Axis Wind Turbine

Horizontal Axis Wind

Turbine

A "normal" wind turbine design, in which the shaft is parallel

to the ground, and the blades are perpendicular to the ground.

Leading Edge The edge of a blade that faces toward the direction of rotation.

Leeward Away from the direction from which the wind blows.

Lift The force exerted by moving air on asymmetrically-shaped

wind generator blades at right angles to the direction ofrelative movement. Ideally, wind generator blades should

produce high Lift and low Drag.

Load Something physical or electrical that absorbs energy. A wind

generator that is connected to a battery bank is loaded. A

disconnected wind generator is NOT loaded, so the blades are

free to spin at very high speed without absorbing any energy

from the wind, and it is in danger of destruction from over-

speeding.

Rotor The blade and hub assembly of a wind generator.

Shaft The rotating part in the center of a wind generator or motorthat transfers power.

Trailing Edge The edge of a blade that faces away from the direction of

rotation.

TSR Tip Speed Ratio Ratio of blade speed to undisturbed wind

speed.

Undisturbed Wind That which occurs naturally.

VAWT Vertical Axis Wind Turbine

Variable Pitch A type of wind turbine rotor where the attack angle of the

blades can be adjusted either automatically or manually.

Vertical Axis WindTurbine

A wind generator design where the rotating shaft isperpendicular to the ground and the cups or blades rotate

parallel to the ground.

Yaw Rotation parallel to the ground. A wind generator yaws to face

winds coming from different directions.


6/20

1

1.0 INTRODUCTION

With the recent surge in fossil fuel prices, demands for cleaner energy sources, and

government funding incentives, wind turbines are becoming a more viable technology for

electrical power generation. Fortunately there is an abundance of wind energy to be

harnessed. Currently, horizontal axis wind turbines (HAWT) dominate commercially

over vertical axis wind turbines (VAWT). However, VAWT do have some advantages

over HAWT.

1.1 Horizontal versus Vertical Axis Wind Turbines

The HAWT is the most common turbine configuration. The propellers and turbine

mechanisms are mounted high above the ground on a huge pedestal. It is a matter of taste

as to whether they enhance the landscape; however, there is no denying that the height at

which their mechanisms are located is a disadvantage when servicing is required. Also,

they require a mechanical yaw system to orient them such that their horizontal axis is

perpendicular to and facing the wind. As potential power generation is related to the

swept area (diameter) of the rotor, more power requires a larger diameter. HAWT blades

experience large thrust and torque forces, and as a result, their size is limited by blade

strength. The effects of increased blade size limit the maximum power output of a

HAWT design. Large capital costs, mainly due to the shear size of the turbine and the

height of the support structure, lead to high initial capital costs associated with HAWT.

A VAWT is omni-directional, meaning that it does not need to be oriented such that it

points into the wind. Another advantage to the VAWT is that the power transition

mechanisms can be mounted at ground level for easy access. However, one of the biggest

advantages of the VAWT is that the blade size can be increased to comprise a larger

swept area, without facing the size limitations as seen in the HAWT. The perceived

disadvantage of the VAWT is that they are not self-starting. However, it could be argued

that the HAWT is also not self-starting, since it requires a yaw mechanism for orientation

purposes. Currently, VAWT are usually rotated automatically until they reach the ratio


7/20

2

between blade speed and undisturbed wind speed (Tip Speed Ratio or TSR) that produces

a torque large enough to do useful work. Through the use of drag devices and/or variable

pitch blade designs, it is hoped that a VAWT will be able to reach the required TSR

without the use of a starter.

Figure 1. Major components of the horizontal axis wind turbine (HAWT) and vertical

axis wind turbine (VAWT) [10].

1.2 Turbine Technology

Turbines relying on drag, such as the anemometer and Savonius models, cannot spin

faster than the wind blows and are thus limited to a TSR of less than 1. Other turbines,

such as the Darrieus, rely on lift to produce a positive torque. Lift type wind turbines can

experience TSR as high as 6. This is possible because the natural wind is vector summed

with the wind opposing the forward velocity of the airfoil. This combined velocity is

known as the relative wind.


8/20

3

In the case of a lift type turbine, the wind imposes two driving forces on the blades; lift

and drag. A force is produced when the wind on the leeward side of the airfoil must travel

a greater distance than that on the windward side. The wind traveling on the windward

side must travel at a greater speed than the wind traveling along the leeward side. This

difference in velocity creates a pressure differential. On the leeward side, a low-pressure

area is created, pulling the airfoil in that direction. This is known as the Bernoullis

Principle. Lift and drag are the components of this force vector perpendicular to and

parallel to the apparent or relative wind, respectively. By increasing the angle of attack,

the distance that the leeward air travels is increased. This increases the velocity of the

leeward air and subsequently the lift.

Lift and drag forces can be broken down into components that are perpendicular (thrust)

and parallel (torque) to their path of travel at any instant. The torque is available to do

useful work, while the thrust, or centrifugal force is the force that must be supported by

the turbines structure.

1.3 Wind Power

The power of the wind is proportional to air density, area of the segment of wind being

considered, and the natural wind speed. The relationships between the above variables are

provided in equation 1 below [1].

Pw = Au3

(1)

where

Pw: power of the wind (Watts)

: air density (kg/m3)

A: area of a segment of the wind being considered (m2)

u: undisturbed wind speed (m/s)


9/20

4

The area considered in equation 1 is associated with the design of the turbine blades. A

parameter called solidity is a number defining how much of the turbines disturbed area,

A, is occupied by the turbines blades. Essentially, a low solidity describes a turbine with

small or fewer blades, while a high solidity indicates larger or more blades.

The main energy advantage realized through wind turbines is that power is proportional

to the wind speed cubed. However, a turbine cannot extract 100% of the winds energy

because some of the winds energy is used in pressure changes occurring across the

turbine blades. This pressure change causes a decrease in velocity and therefore usable

energy. The mechanical power that can be obtained from the wind with an ideal turbine is

given as:

Pm = 0.593 Pw (2)

where

Pm: mechanical power (Watts)

The constant, 0.593, from equation 2 is referred to as the Betz coefficient. The Betz

coefficient tells us that 59.3% of the power in the wind can be extracted in the case of an

ideal turbine. However, an ideal turbine is a theoretical case. Turbine efficiencies in the

range of 35-40% are very good, and this is the case for most large-scale turbines. Other

factors must be taken into account when determining turbine efficiency, including wind

speed, rotational speed of the turbine, and turbine blade parameters such as angle of

attack and pitch angle. Altering these factors changes the efficiency of a turbine.

1.4 Wind Energy Applications

With the current production rates of fossil fuel bi-products, it is not a surprise that

alternative clean energy sources are being heavily researched in an effort to reduce

greenhouse gas emissions. The thought of harnessing energy from the wind is not a far-

fetched idea. Wind turbines are a viable option for providing energy to locations off the


10/20

5

power grid, to small cottages, or for alternative or back up energy sources. They are also

ideal for power generation in remote locations where transportation of fuel may be

difficult and expensive. Although it may seem that this technology is only suitable for

small-scale applications, it is quite the opposite. Large wind farms are an alternative

means of providing power to a large grid. Living in Canada provides Canadians with the

advantage of having a lot of unused land area for wind farm occupancy. This can be seen

currently in Atlantic Canada, with wind farms in both Prince Edward Island and Nova

Scotia. Wind energy can be used anywhere there is wind, and there are no harmful

byproducts associated with this technology.


11/20

6

2.0 PROJECT OBJECTIVE


turbine that has the capability to self-start. The full-scale VAWT will provide a means for

testing various operating and design parameters that affect the turbine performance sothat VAWT technology can be furthered and the energy conversion efficiency of these

devices can be substantially improved. The operating and design parameters that will be

tested are listed below.

Blade Profiles

Currently, two different blade profiles will be used during testing. These are the

cambered NACA 4415 and the symmetrical NACA 0018.

Blade Size

This test will compare the performance of large versus small chord lengths. There

will be two sets of blades for each profile (NACA 001 and 4415); one set with a

chord length of 5, the other set with a chord length of 10.

Blade Pitching

Blade pitching involves the changing of the pitch angle. A spring loaded pitching

mechanism will be designed to change the pitch angle of the turbine. This devicewill allow for both a static pitch angle (constant at all rotational speeds) and a

dynamic pitch angle (changing with rotational speeds).

Two and Three Blades

This test will allow for both 2 and 3 blade configurations to be installed and tested

on the turbine.

Drag DeviceA Savonious-type drag device will be installed in the center of the turbine to study

how it affects turbine performance.

All the above modifications will be tested independently and in combinations to see

which set-up gives the best results. The current test set-up will allow for a torque


12/20

7

transducer to be attached to the turbine, measuring both the torque produced and the

rotational speed. This will also allow for calculation of the power output and turbine

efficiency.

To date, very little information is available regarding the effects of these modifications to

vertical axis wind turbines. Results from the various turbine tests to be carried out may

provide valuable data regarding wind turbine performance under a number of operating

parameters and conditions. Also, it is hoped that this information will promote and

encourage future research at Dalhousie University and in other wind energy associations.

The final turbine will be the property of Dalhousie University upon the groups

completion of the course so that it can be used as a future education and research tool.


13/20

8

3.0 DESIGN PROCESS

As mentioned above, there is limited information surrounding vertical axis wind turbine

technology. As a result, when it came time to design the turbine, there were limited

resources available. To tackle this problem, the group created tools to help in the design

process. First, an Excel model was created to examine the lift and drag forces that airfoils

experience during different turbine rotational speeds, wind speeds, wind angles and

different blade pitch angles. Then, using results from the Excel model, a prototype

turbine was created for testing in the Dalhousie University Wind Tunnel facility. Finally,

using results form both the Excel model and the wind tunnel testing, the full-scale turbine

was designed.

3.1 Excel Model

An Excel Model was created to understand the effects on turbine performance based on a

number of different variables. Model inputs included wind speed, turbine rotational

speed, the angle of attack with respect to the turbine blade and the incoming wind, the

blade size, the number of blades, and the pitch angle of the blades. The model outputs

included centrifugal and inertial forces created for various rotational speeds, performance

results based on 1, 2, and 3 blade designs, and the effects on performance from different

pitch angles. The model was able to provide useful theoretical material to help make

design decisions about the full-scale turbine. However, the group felt it would be wise to

test the model results on a small scale before building a large turbine based on these

theoretical results. This led to prototype testing in the wind tunnel at Dalhousie

University.

3.2 Wind Tunnel Testing

A scale model prototype turbine was constructed and tested in the Dalhousie University

Wind Tunnel Facility. A previous design project set-up was used, as it already allowed

for a torque transducer to measure the torque produced by the turbine, and the turbines

rotational speed. The original testing configuration for the wind tunnel only allowed for


14/20

9

one set of blades to be tested, the NACA 0012 profile. Also, the set-up did not allow for

blade pitching. Our group altered the testing setup to allow for three blade profiles,

NACA 0012, 0018 and 4415, as well as the ability to pitch the blades to a range of

angles. In addition, two sets of arms were made that connect the blades to the central

shaft. One set of arms was made from plywood, and the second set was made from thin

aluminum.

These three sets of blades and two radial arms were tested in a comparative manner to

determine which blades and arms provided the best results. The following observations

were noted:

The thickness of the radial arms affects the maximum rotational speed reached.

With the same wind speed, the aluminum arms (1/8 thick) rotated twice as fast as

the plywood arms (1/2 thick). Subsequently, it was decided for the final product

that the radial connecting arms should be a thin as possible.

The NACA 0018 and 4415 blade profiles provide the best results. Thus, for the

final design, these two profiles will be used, and the NACA 0012 profile will be

abandoned.

Static pitching gave the best results for the NACA 0018 blades. No pitching gave the best results for the NACA 4415 blades.

The prototype turbine blades proved to be easy to make and performed well, and

as a result, the same fabrication process will be used to make the blades for the

full-scale turbine.

Figure 2 shows the prototype turbine arrangement in the Dalhousie University Wind

Tunnel Facility. Also shown in figure 2 is the torque transducer used to measure the

rotational speed and torque from the prototype turbine.


15/20

10

Figure 2. Prototype turbine assembled in the wind tunnel.

3.3 Full Scale Turbine Design

All components of the full-scale turbine have been designed to be as light as possible, but

also withstand the stresses incurred during turbine operation. The full-scale turbine will

stand approximately 10ft tall, with an 8ft diameter. A figure of the final turbine is

provided in figure 3, with each component labeled. The following is a brief description of

each component.


16/20

11

Figure 3. Vertical axis wind turbine assembly [11].

Blades

Base

Roller

Bearings

Shaft

Pitching

Device

Radial

Arms

Drag

Device

CenterMount

Blade Caps

and Pins

One Way

Bearings


17/20

12

Base

The base, made from steel, will hold the turbine upwards. The steel base has been

extended with plywood in an effort to increase turbine stability at high rotational speeds.

The plywood can be covered with sandbags for extra weight if necessary.

Shaft

The shaft will be purchased as 1 solid aluminum. The bottom and top will be milled

down to 1, and the center portion will be milled to 1 1/8. The total shaft height will be

10

Bearings

Two roller bearings will be used in the base to support the shaft. Also, two one-way

bearings will be used where the Savonius drag device is mounted to the shaft. All

bearings will be of high quality to achieve the lowest possible coefficient of friction.

Center Mounts

Two sets of center mounts will be made; one to hold two blades and the other to hold

three blades. These will be CNC machined from aluminum, ensuring a strong yet

lightweight design.

Radial Arms

The radial arms will be made from carbon fiber, due to its favorable strength to weight

ratio. The arms will be 4 in length, with a cross section of x 1. Holes will be drilled

to allow connection to the center mounts and blade caps.

Blades

Four sets of blades will be made from wood. These will consist of two NACA 0018

blades with chord lengths of 5 and 10, and two NACA 4415 blades with chord lengths

of 5 and 10. Each blade will be 5ft long.


18/20

13

Blade Caps and Pins

The blade caps, made from steel, will be used to reinforce the connection pin between the

blade and the radial arm. A cap made from 1/8 steel will be made to the shape of each

blade profile. A 3/8 pin will be inserted through the steel and into the wood blade, with

some of the pin left extruded for connection to the radial arm. The pin will be welded to

limit shear movement, and the whole cap assembly will be bonded to the blade using a

coating of fiberglass.

Pitching Device

The pitching device, which is located on the lower radial arm of each blade, will allow

for static or dynamic pitching. The device consists of a rod connecting the blade to the

radial arm. The rod can be held in place by nuts (static pitching), or the rod can be free to

move, allowing the pitch angle of the blade to change (dynamic pitching). In the case of

dynamic pitching, a spring located at one end of the rod restricts the pitch angles the

blade can achieve, so as to prevent undesired pitch angles or damage to the blades.

Drag Device

A Savonious-type drag device will be made from a lightweight plastic and mounted to the

main shaft via one-way bearings. These bearings will restrict the motion of the device, so

that the drag forces will not hinder the motion of the turbine.


19/20

14

4.0 CONCLUSION


turbine that has the capability to self-start. In addition, this turbine will be designed to

allow a variety of modifications such as blade profile and pitching to be tested.

The first part of the design process, which included research, brainstorming, engineering

analysis, turbine design selection, and prototype testing has been completed. Using these

results, the final full-scale turbine has been designed. Construction of the turbine will

begin in early January, with the goal of finishing the final product by the end of February.

This will allow for a month of testing and data analysis, as well as provide time for

making any design alterations that arise during testing. As a course requirement, thedesign project must be finished and tested by April, so that presentations and final reports

can be completed.

The group is excited about the effects that test results could have on vertical axis wind

turbine technology. There is vast potential for improvements in the vertical turbine field,

and test results will no doubt impact the industry in a positive manner. Efficient

performance of our VAWT could lead to a change in the standard thinking of how wind

energy is harnessed, and may spur future VAWT design and research. As the popular

wind harnessing technology used today is the horizontal axis turbine, the vertical design

offers many advantages and is a cost effective option for capturing larger amounts of

environmentally friendly energy.


20/20

15

REFERENCES

1. Johnson, Dr. Gary L. (November 21, 2001) Wind Turbine Power Ch 4. Wind

Turbine Power, Energy and Torque. Retrieved from

www.eece.ksu.edu/~gjohnson/wind4.pdf in October 2005.

2. Canadian Wind Energy Association. Wind Energy Quick Facts. Retrieved

from http://www.canwea.ca/en/QuickFacts.html in January 2006.

3. Global Wind Energy Council, (2005). A Global Power Source. Retrieved from

www.gewc.net in January 2006.

4. Danish Energy Authority, (Dec 2005). Windturbines Introduction and Basic

Facts. Retrieved from http://www.ens.dk/sw14294.asp in January 2006.

5. Brown, Lester R., (April 2004). Earth Policy Institute - Europe Leading World

Into Age of Wind Energy. Retrieved from www.earth-policy.org/Updates/Update37.htm in January 2006.

6. Natural Resources Canada, (Sept 2005). Wind Power Production Incentive

(WPPI). Retrieved from www.canren.gc.ca in January 2006.

7. CBC News Online, (Nov 25, 2005). Indepth: Kyoto and Beyond, Canada-Kyoto

timeline. Retrieved from www.cbc.ca/news/background/kyoto/timeline.html inJanuary 2006.

8. Peace, Steven, (2004). The American Society of Mechanical Engineers, Feature

Focus: Advanced Energy Systems. Another Approach to Wind. Retrieved fromhttp://www.memagazine.org/backissues/jun04/features/apptowind/apptowind.htm

l in January 2006.

9. Group 2, (December 2005). MECH 4010 Design Project Report: Self-Starting

Vertical Axis Wind Turbine.

10. Natural Resources Canada, (Sept 2002). Wind Energy Technologies and

Applications: Electricity from Turbines. Retrieved from

www.canren.gc.ca/wind/index.asp in January 2006.

11. Group 2, (January 2006). MECH 4020 Design Project - Revised Build Report:Self-Starting Vertical Axis Wind Turbine.

Documents

Energy Ambassador.pdf