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DESIGN and DEVELOPMENT of a VERTICAL AXIS MICRO WIND TURBINE
A dissertation submitted to the University of Manchester for the degree of
Master of Science in the Faculty of Engineering and Physical Sciences
2010
MURAT ISLAM
SCHOOL OF
MECHANICAL, AEROSPACE AND CIVIL ENGINEERING
2
List of Contents
List of Contents 2
List of Tables 5
List of Figures 6
List of Diagrams 9
List of Photographs 10
List of Abbreviations 11
Abstract 12
Declaration 13
Copyright Statement 13
Acknowledgements 14
Chapter 1. INTRODUCTION 15
1.1. Background 15
1.2. Aims and Objectives 15
1.3. Motivations of the thesis 16
1.4. Outline of the Thesis 16
Chapter 2. LITERATURE REVIEW 17
2.1. Fundamental considerations of Resources of Energy 17
2.2. Energy Contained in the Wind 18
2.3. Aerodynamic problems and rotation rate 18
2.4. Life Time and Payback Time of Wind Energy Converters 19
2.5. Effects of Obstacles in Wind Energy Conversion 20
2.6. Electricity Generation from Wind Energy Using VAWTs 22
3
2.7. Wheel Size and Economy 27
2.8. Possible VAWT Components 27
Chapter 3. CONCEPT DESIGN 35
3.1. Engineering Design 35
3.2. Assembly Considerations in Design 36
3.3. Generation of Concepts 37
3.3.1. Frame Concepts 38
3.3.2. Generator Concepts 46
3.3.2.1. Motorcycle alternators 46
3.3.2.2. 3 Phase Handmade PGM Concept 48
3.3.2.3. Printed DC Motor Concept 50
3.3.3. Slip Ring Concepts 52
3.3.4. Impellers 54
3.4. Bearings 56
3.5. Shafts 57
3.6. Aluminium connection for GPM12 and lower shaft 58
Chapter 4. DETAILED DESIGN and MANUFACTURING 61
4.1. Frame Details 61
4.2. GPM12 Printed DC Motor 64
4.3. Critical speeds of rotating shafts 65
4.4. Linear Tolerances 66
4.5. Shaft tolerances for bearings 67
4.6. Tolerance calculations 68
4.6.1. Bearings and shafts 68
4.6.2. Top shaft hole and DC motor shaft 69
Chapter 5. EXPERIMENT AND TESTING 70
4
5.1. Wind Tunnel 70
5.2. Finished components and assembly sequence of the turbine
70
5.3. Experimental Setup 74
5.4. Gathered Data 77
5.4.1. Case 1: Both impellers were freely rotating 77
Chapter 6. DEVELOPMENT OF THE DESIGN 81
6.1. Calculations for Energy Production 81
6.2. Computer Aided Design of Concepts Using Solidworks 82
6.3. Finite Element Analysis Using Abaqus CAE 83
Chapter 7. DISCUSSIONS, FUTURE WORK AND CONCLUSIONS 87
7.1. Discussions on the outcomes 87
7.2. Future works 88
7.3. Conclusions 89
REFERENCES 91
APPENDIX 93
Final Word Count: 13738
5
List of Tables
Table.1 Preferred locations for different turbine mounting
heights (from Heath et al, 2007) ................................................. 21
Table.2 SPARX Alternator test results - 3 Phase HIGH output
Alternator (6V) ........................................................................... 29
Table.3 45x45H Heavy Aluminium Profile Properties[17] ...... 62
Table.4 Typical linear dimensions in BS EN 22768 standard 67
Table.5 20mm shaft tolerances and limiting speeds for Y-
bearings ................................................................................. 68
Table.6 Both propellers rotating: ........................................... 77
Table.7 Upper impeller rotating (lower propeller restrained): . 78
Table.8 Lower impeller rotating (upper impeller restrained) .. 79
Table.9 First 10 natural frequencies of Abaqus model .......... 84
6
List of Figures
Figure.1 Illustration of the main features of flow around a cubic
building ................................................................................. 21
Figure.2 Shape and dimensions of buildings and locations of
possible wind turbine mounting points (perspective and plan
views) in the study by Heath et al (2007) ................................... 22
Figure.3 Rotor concepts with a vertical axis of rotation .......... 25
Figure.4 Vertical axis wind turbine with articulating rotor patent
drawing ................................................................................. 26
Figure.5 Project Nova V shaped vertical axis wind turbine and a
ship next to it ............................................................................. 27
Figure.6 Forward curved centrifugal TABLOCK Blower Wheel[8]
................................................................................. 28
Figure.7 Shimano Nexus-HB-NX70-QR 6v 3.0w quick release
dynamo front hub ....................................................................... 28
Figure.8 a) RFPM machine, b) AFPM machine ...................... 30
Figure.9 Connection diagram of a three-phase, nine-coil
winding of an AFPM brushless machine. ................................... 32
Figure.10 The simple and complex epicyclic gear trains
presented by Lévai .................................................................... 33
Figure.11 a) Epicyclic gear train of the lower arrangement of
quadrant I in Figure.10, b) 3D view of a planetary gear train ...... 34
Figure.12 Selecting the profile of frame (left to right; solid round
bar[16], round tube[16], square tube[16] and slotted profile[17]) 38
Figure.13 Hand sketch of Dr. Oyadiji for CR-VAMWT idea ...... 39
Figure.14 2nd concept hand sketches of frame with indented
bearings ................................................................................. 40
7
Figure.15 Hand sketch of a simpler frame concept (3rd) for four
bearings ................................................................................. 41
Figure.16 Hand sketches of simple structure of wind turbine ... 42
Figure.17 Solidworks drawings of simple structure of wind turbine
................................................................................. 43
Figure.18 Hand sketch of used frame of CR-VAMWT .............. 44
Figure.19 3D drawing of the frame, brackets with fixings and
bearings assembly ..................................................................... 45
Figure.20 SPARX Motorcycle alternator with a rectifier ............ 47
Figure.21 ROYAL Enfield 3 wire - 6 volts Alternator ................. 47
Figure.22 a) Coils, b) Magnets, for 3 phase 12 coils AFPM
handmade generator ................................................................. 49
Figure.23 simplified a) 2D, and b) 3D view of 3 phase 12 coils
handmade AFPM machine showing circuit connections ............ 49
Figure.24 Handmade AFPM machine used with a slipring on a
CR-VAMWT ............................................................................... 50
Figure.25 a) Catalogue photo, and b) Solidworks model of a
Printed GPM12 DC Motor .......................................................... 50
Figure.26 Elements of Printed DC Motors [19] ......................... 51
Figure.27 a) Through bore, and b) Face type slip rings ............ 52
Figure.28 a) Catalogue view [20], and b) Solidworks model of
SPB12 through bore signal & power transfer units ..................... 53
Figure.29 a) D series, b) DD series brush holders, and c) through
bore slip ring [20] ....................................................................... 53
Figure.30 a) Savonius, b) 2 bladed H-Type, and c) 3 bladed H-
Type VAWT concepts ................................................................ 54
Figure.31 a) H-Type & Savonius blades 3D drawing, and b) CR-
VAMWT with Darrieus and Savonius Hand sketch .................... 55
8
Figure.32 Centrifugal Tablock Blower Wheels by Hi-Tech
Blowers Inc. [22] ........................................................................ 56
Figure.33 a) Pedestal, and b) Pillow SKF Bearing Blocks ........ 57
Figure.34 Stepped shaft concept ............................................. 58
Figure.35 C shape thin plate connection concept ..................... 58
Figure.36 Advanced C shape cross connection concept .......... 59
Figure.37 Round cup holder concept ....................................... 60
Figure.38 Final frame with fixings and brackets with central
distances ................................................................................. 61
Figure.39 Chosen Aluminium frame profile drawing ................. 62
Figure.40 500mm length 45x45H 10mm slotted aluminium profile
3D CAD drawing ........................................................................ 64
Figure.41 GPM12 Printed DC Motor ........................................ 64
Figure.42 Schematic of the assembly ...................................... 73
Figure.43 Wind generator experimental circuit with 100W light
bulb , ammeter (A), and voltmeter (V) ........................................ 74
Figure.44 Final CAD Design ..................................................... 75
Figure.45 a) solid shaft model with bearings, wheels and
generator; b) boundary conditions; c) meshed part .................... 83
Figure.46 Mesh on the wheel models (left) and mesh on the DC
motor models (right) ................................................................... 85
Figure.47 Boundary conditions on meshed bearing place ........ 85
Figure.48 First 10 deformation of mode shapes from top left to
bottom right respectively ............................................................ 86
Figure.49 Golden design of the frame ...................................... 89
9
List of Diagrams
Diagram.1 Distribution of yields for installation of SWIFT 1.5 kW
turbine 20
Diagram.2 Impact of low wind speed events 23
Diagram.3 Performance comparison between RFPM and AFPM
machines due to Torque/moment of inertia 31
Diagram.4 Performance comparison between RFPM and AFPM
machines due to Power/active volume 31
Diagram.5 Generated voltage, ampere and power with respect
to the wind speed for Case1 78
Diagram.6 Generated voltage, ampere and power with respect
to the wind speed for Case2 79
Diagram.7 Generated voltage, ampere and power with respect
to the wind speed for Case3 80
10
List of Photographs
Photograph.1 Left photo is free end, and right photo is motor
and fan part of the experiment wind tunnel 70
Photograph.2 GPM12 Printed DC motor and Aluminium cup
holder. 71
Photograph.3 SY20TF Plummer block bearing and SPB12
through bore 2P3S slipring 71
Photograph.4 Assembly of the turbine 72
Photograph.5 Shaft, centrifugal blower wheel and bearings 72
Photograph.6 CR-VAMWT inside the wind tunnel; model (left)
and real (right) 76
Photograph.7 Ammeter with bulb (left), and voltmeter (right) 76
11
List of Abbreviations
Abbr.1 VAMWT: Vertical Axis Micro Wind Turbine 15
Abbr.2 VAWT: Vertical Axis Wind Turbine 23
Abbr.3 AFPM: Axial Flux Permanent Magnet Generator 29
Abbr.4 RFPM: Radial Flux Permanent Magnet Generator 29
Abbr.5 CR-VAMWT: Counter Rotating Vertical Axis Micro Wind
Turbine 39
Abbr.6 PMG: Permanent Magnet Generator 48
Abbr.7 DIY: Do It Yourself 48
Abbr.8 US: Upper shaft (machined from 1m silver steel shaft) 73
Abbr.9 LS: Lower shaft (machined from 1m silver steel shaft) 73
Abbr.10 BW: Centrifugal blower wheel (280mm Width x 280mm
Height) 73
Abbr.11 BR: SY20TF Bearings 73
Abbr.12 SR: SPB12-2P3S Slipring 73
Abbr.13 DC: GPM12 Printed DC motor 73
12
Abstract
Increasing demand in energy facilitated the need of clean energy
such as wind energy. Residences, buildings and commercial sites
needs more power, but also continuous power. Important facilities
such as wireless or radio sets requires small amount of energy,
but with a continuous supply. This study was done to investigate
the design and development of the vertical axis micro wind
turbines. The contribution of counter rotating impellers with a
freely rotating generator to produce energy was investigated. For
the analysis and design, Solidworks, Mathcad and Abaqus CAE
programmes were used. Possible developments were considered.
In conclusion, it was seen that the counter rotating impellers
provide better power production, an increase of six time that of
single impeller ones.
13
Declaration
No portion of the work referred to in the dissertation has been
submitted in support of an application for another degree or
qualification of this or any other university or other institute of
learning.
Copyright Statement
Copyright in text of this dissertation rests with the author. Copies
(by any process) either in full, or of extracts, may be made only in
accordance with instructions given by the author. Details may be
obtained from the appropriate Graduate Office. This page must
form part of any such copies made. Further copies (by any
process) of copies made in accordance with such instructions may
not be made without the permission (in writing) of the author.
The ownership of any intellectual property rights which may be
described in this dissertation is vested in the University of
Manchester, subject to any prior agreement to the contrary, and
may not be made available for use by third parties without the
written permission of the University, which will prescribe the terms
and conditions of any such agreement.
Further information on the conditions under which disclosures and
exploitation may take place is available from the Head of the
School of Mechanical, Aerospace and Civil Engineering.
14
Acknowledgements
I prepared this paper with high support of my parents, my
supervisor Dr.S.O.Oyadiji, my colleague and friend Aggelos
Papazotos, Dr. Steve Burley, Dr. Michael Carroll, Dr. Andrew
Kenaugh and also my proof reader Miss Susan French who has
spent many hours on this paper.
15
Chapter 1. INTRODUCTION
1.1. Background
After the 19th century the demand for electricity escalated. This
high demand caused development of new electric power
generation facilities such as very large onshore and offshore wind
energy farms, solar power plants, wave power plants and tidal
power plants. The idea behind these large scale generation
facilities is decreasing harmful effects of fossil fuels due to NOx
and COy emissions caused by power plants.
1.2. Aims and Objectives
Recently, there is a growing promotion of installation of micro wind
turbines and solar panels in houses. The aim of this study is to
investigate the design and development of micro wind turbines for
integration into residential, commercial and industrial complexes.
Objectives of the study can be listed as;
Understanding of wind power generation and basics of wind
power conversion systems
Effects of obstacles on wind flow and optimal positions of
wind turbines on buildings or landscapes
Understanding effects of wind turbines on the environment
Suggesting convenient impellers and generators for
(VAMWT)
Designing and testing of a micro wind turbine to suggest
further developments
Abbr.1 VAMWT: Vertical Axis Micro Wind Turbine
16
1.3. Motivations of the thesis
The high energy demand in the world causes new interest in
different energy areas. Instead of the fossil fuels or non-renewable
energy resources, human realised the necessity of renewable
energies to cleanse the world.
Wind turbines are one of the cleanest energy production
machines, as they only require wind energy and maintenance to
produce power. With the increasing wind energy market, in the
close future, there will be many houses mounted with wind
generators are estimated.
Another reason of studying this subject is the disciplines that it
requires to use. With studying this subject, one can learn about
computer aided design, finite element analysis, fluid mechanics,
statics and dynamics, etc. which makes the designers more
experienced as an engineer in what they are doing.
1.4. Outline of the Thesis
This study will start with a through literature review to obtain
enough basic knowledge about wind turbines. After literature
review the basic concepts will be considered, and then the best
concepts will be discussed. The best concepts will be detailed and
then manufacturing problems will be considered. An experiment of
the designed micro wind turbine will be presented and obtained
results of the experiment will be discussed. A simple analysis of
the design will be made using CAD and FEA software such as
Solidworks and Abaqus CAE, also Mathcad will be used to
calculate power requirements and possible productions. After all,
general discussion, future aspects and conclusions will be made.
17
Chapter 2. LITERATURE REVIEW
Before starting any design process, one should have a good
knowledge about the field of study. Today, the main source of
basic and advanced information can be seen as online libraries
rather than library buildings. However, a good literature review
should include many different sources of information. This
literature review is written to shows the understanding of the
author in the field of wind energy as well as the main
considerations about VAMWTs.
2.1. Fundamental considerations of Resources of Energy
The sun's heat on the earth's crust triggers air to have different
pressures causing the wind to blow, which defines the wind as a
renewable energy. One of the best ways to gather wind‟s energy,
and therefore the power, is using high efficiency wind turbines[1].
The reasons behind choosing and using wind energy instead of
other sources are explained in the following paragraphs.
Fossil based resources are becoming exhausted and gradually
getting expensive. Also the diverse distribution of these resources
on the earth causes many problems. In addition, they are polluting
the earth with their high „carbon footprint‟. Thermal power stations
are using high fuel based resources to generate heat and
eventually electricity. As the fuel has to be transported, these
stations require a large labour force and also need maintaining.
On the other hand, we have renewable energy resources such as,
water power, wind power, tides and solar power. Usually these
resources require very high capitals and first construction
expenses. Also, they are mostly dependent on the availability. For
18
example, while United Kingdom does not get much solar energy,
Africa has an abundance of tidal energy which can only be useful
if there is wide connection with the sea. Even though these
problems exist, they are still better than the non-renewable
resources. They require less labour force, therefore less
maintenance and operation costs. They have considerably less
polluting effects and less intrusion on the environment than the
non-renewables.
2.2. Energy Contained in the Wind
The main source of the earth‟s power is from the sun and it is
approximately 1.484x1018 kWh/year [2]. Only 2.5% of this energy
is said to be converted into energy of motion of atmosphere.
Therefore, the total kinetic energy of the air, which is related to
wind, can be estimated as 2.5x1014 kWh. Most of this power is
stored in very high altitudes usually 8km to 14km from the ground
level. While the average wind speed is about 3 to 14 m/s around
the surface of the earth, it is about 18 to 26 m/s above 8km high.
However, because of turbulences in the air, the high wind speeds
can also be seen in the lower layers of atmosphere [2].
2.3. Aerodynamic problems and rotation rate
Rotation rate of a wind turbine rotor is directly related to its blade
aerodynamics. Centrifugal blower wheels have a specific tip
speed ratio which is the tip speed of the wheel proportional to
wind speed. Rotation rate also affects the power output of a wind
turbine as it has been known since the 1970s. In addition, to
obtain a high rotation rate coefficient; while radius is increased,
the width of the blades should be decreased. This phenomenon
19
causes difficulties in maintaining structural strength and also
static/dynamic control of the blades. [2]
2.4. Life Time and Payback Time of Wind Energy Converters
Micro wind turbines are generally used to supply electricity to
buildings, which are also known as small-scale wind energy
sources, rated less than 50 kW. New turbine products are
supported by the Department for Business, Enterprise and
Regulatory Reform (BERR), Low Carbon Buildings Programme
grant scheme made available in the recent market [3].
The manufacturing, installation and operation of every product
produce carbon emission. The lifecycle carbon of small scale wind
energy was widely studied by many researchers. A report from
Edinburgh University cites that a Swift turbine 1.5 kW machine
which is roof mounted and grid connected, has a 13 and 20
months carbon payback time [3]. Furthermore, in 2008, it was
found that under suitable wind conditions small wind turbines
generally pay back their carbon emissions within a few months to
a few years. Diagram.1 illustrates the data obtained from an
Edinburgh paper. This diagram assumes that the whole UK
household population had installed small wind turbines to their
buildings in urban areas. This analysis is only indicative. Many
small roof swift wind turbine installations may not pay back the
carbon emitted during their production and operation.
20
Diagram.1 Distribution of yields for installation of SWIFT 1.5
kW turbine
The UK wind turbine market is growing according to recent
surveys; however fewer turbines have been sold in the UK than
other countries such as the USA and reportedly there were over
150000 machines installed and operated worldwide until 2008.
Many people and organizations are likely to buy small wind
turbines to install in their houses and commercial buildings after
recognition of climate change due to carbon emissions which will
be considerably reduced by 15% by 2050 [3].
Microgeneration technology assumes that its particular use is
supplying electricity to buildings directly but an important fact is
shape and location effects of buildings as well as demand of
electricity. On the basis of required high wind speeds by common
wind turbines, micro wind turbines are designed to work in also
low wind speeds which are likely to be seen in urban areas.
2.5. Effects of Obstacles in Wind Energy Conversion
The buildings have a big effect on the air flow in the atmospheric
boundary layer which causes urban areas to have lower wind
21
speeds than rural areas whilst approaching to the ground. These
effects have been studied by Hunt et al (1978), Meroney (1982)
and Hosker (1984) [4]. Figure.1 is a simplified view of wind flows
around a cubic obstacle on the ground. Straight air flow creates a
curve while hitting the front top edge of the obstacle and a
recirculation region occurs behind it. This effect plays an immense
role on the boundary layer of air flow and requires some
considerations for the installation locations of micro wind turbines.
Figure.1 Illustration of the main features of flow around a cubic
building
The placement of wind turbines on top of building was studied by
Heath et al (2007) and the results were given in Table.1 and
Figure.2.
Table.1 Preferred locations for different turbine mounting heights (from Heath et al, 2007)
22
Figure.2 Shape and dimensions of buildings and locations of
possible wind turbine mounting points (perspective and plan
views) in the study by Heath et al (2007)
While wind speed goes below 4 m/s large wind turbines may not
produce electricity. Very high inertia of blades and generator
prevents rotation of blades and even though rotation occurs, low
rotational speed causes insufficient production of electricity.
Sometimes across the whole UK, the wind blows below 4 m/s
according to UK Met Office records. However, it is more usual to
see low wind speeds in individual wind sites where ail hours of
wind blow is around 15-20%, while on average 90% of the UK
households are subjected to around one hour low wind speed
conditions per year. And also the summer period has slightly more
ail hours than the winter period. These impacts of low wind speed
amongst areas of the UK are given in Diagram.2 .
2.6. Electricity Generation from Wind Energy Using VAWTs
There are many types of electric generators to convert kinetic
energy of an air stream and many concepts or designs remain
useless because the necessary attention was not given to other
components such as gearbox, generator, control systems and a
variety of auxiliary units as well as wind rotors. Wind energy
converter classifications are determined with respect to
aerodynamic function and constructional design.
23
Diagram.2 Impact of low wind speed events
Abbr.2 VAWT: Vertical Axis Wind Turbine
“Drag-type rotors” uses drag effect of air stream over surfaces and
others use aerodynamic lift effect “rotor which makes use of
aerodynamic lift effect”. “Low-speed and high-speed rotors” are
determined by aerodynamic “tip-speed ratio” of rotors [5].
Constructional design classification is more common than
aerodynamic function classification due to easy recognition.
Position of wind rotor axis of rotation is the most obvious
characteristic of a wind turbine, so they were classified as “vertical
axis” and “horizontal axis” wind turbines. And also “wind energy
concentrators” are used to focus the air stream into turbine blades
to increase the efficiency.
In accordance with investigating design and development of
vertical axis wind turbine for residential, commercial or industrial
use, it is necessary to create some concepts and make some
24
experiments with the designs. To make the design simple, some
basic components needed to be determined in advance. Wind
turbine was suggested as it has counter rotating blades and an
array of this micro turbine will be placed to create the required
electricity. Instead of using complex Darrieus rotors, blower fan
blades and Savonius rotors were considered as alternatives.
Electricity production devices were chosen as alternators,
dynamos or axial flux permanent magnet generators to discuss.
Increasing rotational speed was required to have gears and
planetary gear concept was seen as appropriate. The next stage
of this literature review will discuss benefits and disadvantages of
components and recent wind generator machines.
Vertical axis wind rotors are the first type of wind energy
converters seen in the world. At first they could only use pure
drag-type rotors like the “Savonius rotor”. Ventilators on rail road
carriages or delivery vans, and anemometer rotors are good
examples of vertical axis of rotation. However, later, French
engineer Darrieus built a blade also using aerodynamic lift known
as the “Darrieus rotor”. Darrieus rotor blades have a troposkien
shape (i.e. “turning rope” in Greek) which has vertical axis of
rotation. Due to its complicated shape, manufacturing of Darrieus
rotors are difficult. The benefits of vertical axis wind turbines
(VAWT) can be listed as; its simple design features allows them to
place other components on the ground level, yawing systems are
not needed, functions well in turbulent conditions and constantly
connected to wind without losing power. However, they have low
tip-speed ratios, their self-start ability is weak, and the power
output cannot be controlled by pitching rotor blades. H-rotors
which have straight blades connected to shaft by struts were
25
developed as a variation of Darrieus rotors, and they were made
in the UK, USA and in Germany for commercial use. H-rotors
have better ability of power and speed control than Darrieus
rotors. High manufacturing costs of vertical axis wind turbines
started to decrease but still it is hard to compete with horizontal
axis turbines. However, Darrieus rotors have the potential for
improvement so they might overcome their disadvantages.
Figure.3 Rotor concepts with a vertical axis of rotation
The Savonius design is used for small, simple wind rotors like for
driving small water pumps. The low tip-speed ratio and
comparatively low power coefficient of Savonius prevents it being
used as an electricity generating machine. When it is optimized
then its power coefficient approaches 0.25 which still looks low [5].
Apart from these developments, a tilt rotor wind generator patent
has been claimed by the Blackhawk Company. The inventor of the
patent (US 7,677,862 B2) is Bruce E. Boatner [6]. Figure.4 shows
the recent patent scheme. This patent includes pitch control
systems so, it can manage wind speeds. In this patent there is at
least one mechanical linkage to vary airfoil pitch according to rotor
26
tilt. Also when the engine shuts down airfoils can be closed, so
wind damage can be prevented upon airfoils.
Figure.4 Vertical axis wind turbine with articulating rotor patent
drawing
In addition a large scale V-shaped vertical axis offshore wind
turbine was developed in the name of “Project NOVA (Novel
Offshore Vertical Axis)”. This huge wind generator can produce 5
to 10 MW electricity and there will be new productions by 2020 [7].
27
Figure.5 Project Nova V shaped vertical axis wind turbine and a
ship next to it
2.7. Wheel Size and Economy
Large wind turbines have very high inertias in addition to very high
power transmission requirements. These high powers
(megawatts) bring the need for gear sets to increase the
generator shaft speed in order to get sufficient power output.
Therefore, the weight of the installation increases drastically.
Tower structure becomes bigger and costs more. To reduce the
cost and increase the output of the wind turbine, all inertias and
weights should be reduced. [2]
2.8. Possible VAWT Components
Blower fan blades are used in blower machines as rotational
movements of fans are converted into air flow. In a VAWT, it can
be used in the opposite way to create rotational movement from
air flow. As they are readily built and applicable components, for a
test design they will be used as VAWT rotors. Inertia of a blower
fan blade is considerably high and the efficiency of blades is low
in relation to Savonius blades due to reverse flow effect on blades
28
at both sides of rotation axis. For a micro wind turbine small sizes
of blower fan blades are considerably suitable.
Figure.6 Forward curved centrifugal TABLOCK Blower
Wheel[8]
Initially bicycle dynamos were considered as generators. However
their very low power capacities weren‟t seen as convenient for
wind turbine concept although they have self bearings. Shimano
has produced the HB-NX70-QR model which is shown in Figure.7
[9]. Most of the bicycle dynamos only produce 3 W of electricity
which is enough for a couple of bicycle lamps.
Figure.7 Shimano Nexus-HB-NX70-QR 6v 3.0w quick release
dynamo front hub
Motorcycle alternators were another option for generating
electricity for a micro wind turbine; however they require very high
rotational speed. The amount of power they can produce is
significantly related to their relative angular velocity. Test results
29
of a 3 phase high output alternator is given the below table.
Obtained results show that below 2000 revolutions per minute,
140 W power of electricity can only be produced by alternators
which costs around £150 [10].
Table.2 SPARX Alternator test results - 3 Phase HIGH output Alternator (6V)
RPM STD ALT (AMPS)
STD ALT (WATTS)
SPARX ALT (AMPS)
SPARX ALT (WATTS)
2000 3.75 52.5 10 140 3000 12.5 175 13.25 185.5
New materials, innovations in manufacturing technology and
development in cooling techniques improved the performance of
recent generators. Radial flux permanent magnet (RFPM)
machines have a limited power density due to their bottle-neck
flux path at the root of the rotor tooth regarding induction DC
commutator machines or brushless machines with external
motors. Furthermore, there is very poor heat removal to the frame
of motor. On the other hand, axial flux permanent magnet (AFPM)
machines have a higher power density than RFPM machines and
it is more compact.
Abbr.3 AFPM: Axial Flux Permanent Magnet Generator
Abbr.4 RFPM: Radial Flux Permanent Magnet Generator
30
Figure.8 a) RFPM machine, b) AFPM machine
In accordance with to bigger inner diameter of AFPM machine
than shaft, better cooling is provided. The air gap in AFPM
machines comparatively somewhat adjustable so more core
material can be saved or power-torque requirements are easily
managed. Produced power can be increased using larger outer
diameter of core and higher number of poles which is suitable for
low speed or high frequency operations in AFPM machines.
Research, about the comparison between RFPM and AFPM
machines, shows that AFPM machines are more suitable for wind
turbine designs. Obtained tables show that single gap AFPM
machine provide good results and can be used to produce more
power. [11]
31
Diagram.3 Performance comparison between RFPM and
AFPM machines due to Torque/moment of inertia
Diagram.4 Performance comparison between RFPM and
AFPM machines due to Power/active volume
32
Since electromagnetic torque in RFPM machines is proportional to
the square of the outer diameter times the length, it is cube of the
outer diameter in AFPM machines as shown in (E.1) . [11]
(E.1) Equation of electromagnetic torque for a AFPM
machine
Single layer of trapezoidally shaped evenly placed coils are
accommodated in stator winding for AFPM machine. Epoxy resin
and hardener is used to locate windings which are held together.
Another coil profile is rhomboidal coil for coreless stator AFPM
machines which has shorter end connections than trapezoidal
coils; however torque is reduced in rhomboidal coils. Connection
of 3 phase nine trapezoidal coil winding of an AFPM machine is
shown in Figure.9. [11]
Figure.9 Connection diagram of a three-phase, nine-coil
winding of an AFPM brushless machine.
Increasing rotational speed also increases the power output.
Achieving this goal is related to the use of gears in micro wind
33
machines. Instead of using normal gearbox sets, planetary gears
which are also known as epicyclic gears are considered due to
their compact structures. There are many different modifications
of planetary gear arrangements, and some of them are shown in
Figure.10.
Figure.10 The simple and complex epicyclic gear trains
presented by Lévai
A planetary gear is described as any gear set which includes at
least one gear that rotates about its own axis and also about the
axis of an arm or carrier [12]. Epicyclic trains are classified in
Figure.11 as quadrant I and III are simple epicyclic trains and II
and IV is complex epicyclic trains. However, only one planet
carrier (ring) can be used in any of the arrangements.
For an epicyclic trains system of 20 teeth sun gear, 30 teeth
planet gear and 80 teeth ring gear, while ring gear is fixed and sun
gear is rotating with 1000 rpm and clockwise then direction of
rotation and rotation speed of planetary gears is calculated as 333
rpm counter clockwise and for final drive it is 200 rpm and
clockwise [13]. When sun gear diameter is lower than planet gear,
both shafts turn in the same direction, but if higher, then shafts
turn in opposite direction.
34
a) , b)
Figure.11 a) Epicyclic gear train of the lower arrangement of
quadrant I in Figure.10, b) 3D view of a planetary gear train
According to this literature review, constructing a horizontal axis
micro wind turbine array is possible and may provide the power
that a residential, commercial or industrial complex needs
regarding to good design concepts. In conclusion, micro VAWT
arrays will reduce carbon emissions and fossil fuel consumption.
The array will usually be placed on the corner of a high building‟s
roof and for a basic experiment of a counter rotating VAWT,
Savonius rotors and blower fan blades should be used. Also an
AFPM alternator is more convenient for a counter rotating VAWT
using planetary gears with fixed outer ring and small planet gear
diameter than sun gear diameter to put the gear in between. Thus,
AFPM alternator‟s permanent magnet part will be fixed to planet
gear‟s rotation axes and the coil part will be fixed to the sun gear
shaft. As a result of counter rotation, generated electricity should
be transmitted by a brush on one shaft to an electric accumulator.
To convert created AC current to DC current a rectifier may be
included in the system.
35
Chapter 3. CONCEPT DESIGN
3.1. Engineering Design
In this thesis, heuristic method is used to complete the task of
design of a vertical axis micro wind turbine. It was imagined that
the task has been completed and all the targets were reached
[14]. Design was made step by step moving towards the
beginning. When the beginning is found then the whole design
specifications are achieved.
The main consideration of the wind turbine was its counter
rotating blades that reduce the inertia and increase the relative
speed of the motor shaft. It must have a frame to hold the
bearings and two identical counter rotating blade components
such as Savonius or Darrieus type blades, etc. these two blade
components should be connected to two different shafts. Then,
the torque should be gathered through a generator whose stator is
connected to one of the shafts while the rotor is connected to the
other shaft. As the two separate shafts are connected to the
generator, the power has to be transmitted by a slipring to a
battery tank, the grid or the experimental measurement devices.
Using these basic considerations, design process has been
iterated and finally the best concept was chosen.
“Once you identify a problem, it’s easy to fix it.” Peter Chaconas
[14]
To be able to say all the targets are finished during the heuristic
method approach, the need must be specified. The statement of
the need is actually the beginning and the most significant part of
the solution to the problem. Without a „need statement‟ or
36
providing a complex one, the design can either be restrained too
much or going in a completely wrong and very long way. The
definition of the need for this thesis was defined as; Design and
development of a vertical axis micro wind turbine.
As soon as the need was defined, ideas started to be generated.
Without looking at the literature, possible solutions to the problem
were contemplated. Due to time restrictions, after gathering more
than three concepts the most appropriate one was tried to be
chosen. After choosing this concept, the decision of selecting one
of three possible ways was made; continuing to the final design,
going back/redo the concept design or terminate the project [14].
3.2. Assembly Considerations in Design
In order to design a component, there are some questions
(suggested by M. Myrup Andreasen et al. 1983) to be answered
such as; „Which material should be used?‟, „How should they be
produced?‟ and „How should the assembly be done?‟ [15]. These
questions will be answered in the following sections of the
dissertation. Some of the assembly methods can be listed as
composing by; joining, filling, interference, phase changes,
change of form, means of material, etc. [15]
In the assembly process, there are 7 points of interest to be
concerned with; degrees of freedom (movement), material
differentiation, product and establishment (replace ability)
considerations, differentiation of functions, particular functional
conditions and design considerations. All these points are
examined during the complete concept design process.
37
3.3. Generation of Concepts
For a design engineer, one of the most important abilities is
“creation”. There are many methods to be used to generate ideas
such as brain storming which familiar to many people nowadays.
However, to design a machine, we also suggest making hand
sketches of the basic components and try to link them to each
other on the paper. The links can only be improved, if the principle
connection methods are all known.
The best solution is the one that satisfies the requirements with
minimum cost and time consumption. The wind turbine design
was carefully planned as it will be used for further studies, in order
that the design is made with more than enough strength and
without any requirement to have high efficacy from the blades or
the turbine itself. The main consideration was proving the idea of
counter rotating vertical axis wind turbines have better self start
abilities while they produce a similar or greater amount of energy
output than the normal wind turbines which have the same size of
cross sectional area of blades facing the wind flow. Concepts
have been created by selecting individual components due to the
criteria suggested below;
Mounted bearings will be used
Two identical counter rotating impellers will be used
Minimum total cost and manufacturing time
Maximum flexibility of design as it will be used for further
studies (e.g. PhD degree related experiments)
Improved self-start ability and power generation
38
3.3.1. Frame Concepts
The frame is the basic component to support the essential parts of
the wind turbine. It must be sturdy enough to compensate the
static forces such as the weight of the wind turbine and tightening
forces due to screws or bolts, and particularly dynamic forces
such as vibrations due to rotating elements and fluctuating thrust
force over the turbine due to blowing wind.
The very first idea of the cross section of the frame was chosen as
it could be a round solid bar to provide better structural strength
and less obstruction effect on the wind flow. Then it was thought
that the strength of the solid bar was unnecessarily high, such that
a round tube was suggested. Taking into account ease of
assembly, it was thought that a square cross section hollow tube
would be better to use. However, after searching deeper with
reference to the frames used for some applications, it was
realised that aluminium profiles with slots are very easy to
assemble and also can be very strong. So that, finally, the cross
section of the frame was selected as a slotted profile. The
generation of the profile of the frame was shown in the following
figures which were taken from websites.
Figure.12 Selecting the profile of frame (left to right; solid round
bar[16], round tube[16], square tube[16] and slotted profile[17])
39
While selecting the frame profile, also the shape of the frame was
considered. The idea was suggested by Dr. S. Olutunde Oyadiji
who supervised this dissertation and also sketched the CR-
VAMWT starting idea of this dissertation as shown in Figure.13.
Abbr.5 CR-VAMWT: Counter Rotating Vertical Axis Micro
Wind Turbine
In the Figure.13, it is seen that there are two identical blades
which are turning in opposite directions inside the frame.
Approximate dimensions were also given in millimetres and
suggested that the turbine is in micro scale.
Figure.13 Hand sketch of Dr. Oyadiji for CR-VAMWT idea
The second concept of the frame (Figure.14) was suggested as
the bearings might be pushed in to the blades to increase the
dynamic stability of the shafts which enables us to use less
amount of shaft material. Additionally, this idea leads to having
40
less inertia of total rotating elements, so that the self start ability
could have been improved.
The counter rotating property of the turbine necessitates using a
generator or alternator in between the impellers. Increasing this
space leads to a bigger turbine area whilst having a small size of
impellers. Pertaining to this fact, frame cross section area should
be selected as small as possible, while providing enough strength
values. In addition, putting the frame structure inside the impellers
causes turbulence of air which reduces the expected life time of
the whole wind turbine.
Figure.14 2nd concept hand sketches of frame with indented
bearings
After considering these disadvantages in the 2nd concept, another
concept has been suggested as four bearings which should be
placed on a simple structure as shown in Figure.15, Figure.16 and
Figure.17.
41
While creating the sketches, except for making the idea workable,
there were no other objectives. Therefore the sketches include
many unrelated meaningless scribbles purely for the intention to
stimulate the designer‟s mind, and to enable clarity and vision. An
important factor for designers is to take satisfaction and pleasure
in generating new concepts, in order that they feel their final
design be worthy of their clients.
The 3rd concept consists of four horizontal profiles supported by
two vertical ones which were placed on two other horizontal
profiles which can easily be seen in Figure.16 with the 3D
drawing. In this drawing also bearings were put on the profiles
with 2 different shafts which have a common generator or
alternator in between.
Figure.15 Hand sketch of a simpler frame concept (3rd) for four
bearings
42
Turbine impellers were also included in the drawing. This concept
was considered as the one which should be developed and
designed in detail for the frame, shafts, impellers and bearings.
Created Solidworks sketches were printed to enable the designer
to create better ideas on them by doing some scribbles or giving
the approximate dimensions. Also these hard copies were used to
discuss the ideas with different people from any background. They
could be supervisors or even a housewife. The best designs are
the ones which are the simplest ones doing the same job as
others.
Figure.16 Hand sketches of simple structure of wind turbine
43
The 3D CAD programs enables the designers see their design‟s
exact dimensions in 3D which makes the feasibility of the machine
clearer. Possible interceptions, assembly difficulties or even
movements of the elements can be seen clearly. And also, saving
these files as pictures creates images in designers‟ minds and
new ideas can be developed by recollecting and combining all of
these images.
Figure.17 Solidworks drawings of simple structure of wind
turbine
44
After the general shape of the wind turbine had been decided,
hand sketch of the real frame which is shown in Figure.18 was
created.
Figure.18 Hand sketch of used frame of CR-VAMWT
The frame is supported by brackets with fixings which are
suggested by kjn Aluminium Profile & Accessories Ltd. Company
[17]. After having this sketch done, a 3D drawing shown in
Figure.19 was created in Solidworks platform. In this drawing
components were coloured individually and it can be seen that
having different colours of elements have made the design more
logical.
45
Figure.19 3D drawing of the frame, brackets with fixings and
bearings assembly
This concept was chosen as the best one for this thesis because;
it is very easy to adjust for different purpose of studies, such as
assembling it in a different way in an hour without any other
manufacturing process. It has slots to put other bolts and nuts
which enable using other components on the structure such as
guide vanes for wind flow. In addition, the slots could be covered
with plastic caps to lessen the turbulence of the air flow. Moreover
power or signal input/output wires can be put in these covered
slots. The frame is very stable against loads due to its strong
profiles and brackets.
46
3.3.2. Generator Concepts
Generators or alternators are used in all wind turbines to produce
the electricity as DC or AC output. However, batteries can only
store DC current and those results in AC generators or alternators
being used with a rectifier to change the current into DC. In this
thesis, to produce the electricity; motorcycle alternators, bicycle
dynamos, DC electric motors and handmade permanent magnet
alternator concepts were considered.
Apart from current type as DC or AC, the generator type also has
an important effect on generating electricity. AFPM or RFPM
machines should be analysed for their characteristics.
According to shaft, which has smaller diameter than the AFPM
machine itself, better cooling is provided. Air gaps in AFPM
machines are comparatively somewhat adjustable, so that more
core material can be saved and power-torque requirements can
easily be managed. Produced power can be increased using
larger outer diameter of core and higher number of poles which is
suitable for low speed or high frequency operations in AFPM
machines. Research, about the comparison between RFPM and
AFPM machines, shows that AFPM machines are more
convenient for wind turbine designs. Obtained tables show that
single gap AFPM machine provides good results and can be used
to produce more power. [11]
3.3.2.1. Motorcycle alternators
Motorcycles have an RFPM machine which is the alternator, to
convert motor power into electricity to supply its lights and
electronic parts such as displays. Although the necessity of power
depends on the size of the motorcycle, generally they have a
47
power output of 70W to 215W with a voltage of 6 volts or 12 volts
while they are being used with 2000 to 8000 RPM [10].
The model SPX003, SPARX 3 phase alternator kit with 210W
(regulated at 14 volts) of power output has a price of about £170
in the current market.
Figure.20 SPARX Motorcycle alternator with a rectifier
The model ROYAL Enfield 3 wire 6 volts alternator sets for old
models cost about £70 in the market, however, it produce far less
electricity than SPX003 [18].
Figure.21 ROYAL Enfield 3 wire - 6 volts Alternator
Dimensions of motorcycle alternators are very comparable to
each other. Differences can be seen as a few centimetres. Royal
Enfield alternator has an outside diameter of 12.6cm and a width
of 3.7cm. These dimensions show that, ready-made motorcycle
48
alternators are good dimensionally to fit in a micro wind turbine as
they only have a few meters of height.
For CR-VAMWTs it is always better to use a light generator
because of the fact that it needs to be rotate totally. Increasing
weight increases the necessary wind speed required to self start,
due to higher inertia. Motorcycle alternators are built with a very
strong structure designed for the occurrence of high vibrations
and dynamic forces of the motorcycles. This strong structure
requires heavy materials and increases the weight of the
alternator. On the other hand, bicycle dynamos are really light and
would be considered as the second option for generators but they
do not produce much power.
Motorcycle alternators were not chosen as the generator, as they
require a rectifier but more importantly they require high rotational
speeds to alternate current in order to produce power. Gear sets
are likely to be used in wind turbines with motorcycle alternators.
3.3.2.2. 3 Phase Handmade PGM Concept
There a lot of DIY wind generators which can be found on the
internet through many websites just using the keywords of DIY,
wind and turbine. Most of these websites contain some
instructions about how to build a 3 phase PMG which is an AFPM
machine.
Abbr.6 PMG: Permanent Magnet Generator
Abbr.7 DIY: Do It Yourself
Handmade PMGs can be designed for the specific purposes such
as power requirements or space requirements. They are very
small in width and broad in diameter which makes them very
49
useful for CR-VAMWTs. Although the small air gap between
facing surfaces of magnets and coils might cause problems due to
vibrations, the wide diameter causes them to have high relative
speed and thus more power output. Handmade PGMs would have
been chosen as the generator, but the manufacturing time of
these components is quite long for this thesis.
a) b)
Figure.22 a) Coils, b) Magnets, for 3 phase 12 coils AFPM
handmade generator
a) b)
Figure.23 simplified a) 2D, and b) 3D view of 3 phase 12 coils
handmade AFPM machine showing circuit connections
Power output of these machines depends on the magnetic field
strength of magnets, wire resistance, diameter of the magnets &
coils, number of rotations and length of wire in each coil and also
the air gap in between coils and magnets apart from relative
rotational speed of magnets and coils. In Figure.22 and Figure.23
50
it can be seen that these machines have very big outside diameter
to width ratios.
Figure.24 Handmade AFPM machine used with a slipring on a
CR-VAMWT
A good design can be produced only with a good experience and
knowledge of these components and characteristics of them.
Again this dissertation had a very limited time to produce such a
good design, so that it was not chosen as the final concept.
3.3.2.3. Printed DC Motor Concept
a) b)
Figure.25 a) Catalogue photo, and b) Solidworks model of a
Printed GPM12 DC Motor
51
Printed DC motors are a kind of improved AFPM machines. They
are also known as Printed Circuit (PCB) or "Pancake" Motors [19].
Printed DC motors have very thin structure because the wires are
placed on a thin disk and the magnets are relatively small.
Figure.26 Elements of Printed DC Motors [19]
As shown in the Figure.26 rotation of the motor is directing the
current through the printed wires by a magnetic field of permanent
magnets. The printed motor has guided magnetic fields so that the
power produced is very efficient. Like all DC motors this machine
has a commutator to take the current out through two wires.
These motors can produce about the same amount of electricity
as motorcycle alternators with similar rotational speeds, while they
have far less inertia due to small weight. Because of their small
dimensions and small inertias which are less than motorcycle
alternators and also their highly efficient power output, this
52
concept was chosen for being detailed in design in the next
chapter.
3.3.3. Slip Ring Concepts
Sliprings can transmit electricity for the purpose of power or signal
transmission over a rotating component to another fixed or
rotating component. Sliprings have brushes which contact with
copper rings during which time any of them or both are rotating. In
this thesis to take power out of the rotating generator, it was
necessary to use a slipring. Although there are many types of
sliprings, only through bore and face type sliprings were
considered for use as shown in Figure.27.
a) b)
Figure.27 a) Through bore, and b) Face type slip rings
Face type slipring would have been used in connection with the
generator. Therefore more space would have been saved due to
their thin structure. However, manufacturing difficulties for this
small study governed the use of a through bore slipring, which is
easier to assemble and has no important manufacturing
necessity. Sliprings were chosen due to their capabilities as they
53
should withstand the required rotation speeds. Moreover, their
sizes and inertias should be comparatively small. Figure.28 shows
SPB12 through bore slipring catalogue view from BGB
Engineering Ltd and also its 3D CAD drawing in solidworks.
a) b)
Figure.28 a) Catalogue view [20], and b) Solidworks model of
SPB12 through bore signal & power transfer units
Apart from these ready-made sliprings, also customised sliprings
would have been used. Figure.29 indicates the main components
of a through bore slipring that one can put in to any assembly as
required. Nevertheless, they require trained personnel to make
the assembly and also high security precautions. A risk
assessment form is also included in the appendix. This kind of
customised slipring is also depicted in Figure.24 using a DD
series brush holder.
a) b) c)
Figure.29 a) D series, b) DD series brush holders, and c)
through bore slip ring [20]
54
3.3.4. Impellers
The first improvement in vertical axis wind turbines was started
after the invention of Savonius blades. The low rotational speeds
and efficiency of Savonius blades caused low power productions
so that new interest in improved blade shapes such as Darrieus
blades came into account as shown in Figure.30.
a) b) c)
Figure.30 a) Savonius, b) 2 bladed H-Type, and c) 3 bladed H-
Type VAWT concepts
Another configuration of Darrieus blades is suggested as H-Type
blades, which are lift also based blades, having a higher efficiency
than Savonius blades. However, H-Type or Darrieus blades do
not self start as easily as Savonius blades, so that they usually
require another actuator.
55
In the study of Elmabrok, it was suggested that using a Darrieus
blade together with a Savonius blade has better performance than
using them individually according to self-start ability and efficiency
of the turbine [21]. We can develop this idea with suggesting a
more efficient H-Type blade used with a Savonius blade, and
moreover using them in a counter rotating way to improve the
performance as shown in Figure.31.
a) b)
Figure.31 a) H-Type & Savonius blades 3D drawing, and b) CR-
VAMWT with Darrieus and Savonius Hand sketch
On the other hand, to reduce the manufacturing and also
assembly time none of these concepts were used in the
experiment of this thesis. Instead of these, ready-made forward
curved centrifugal blower wheels were suggested which are
shown in Figure.32.
56
Figure.32 Centrifugal Tablock Blower Wheels by Hi-Tech
Blowers Inc. [22]
Normally these components are used to push the air through air
ducts to condition the air of buildings. Their efficiency is generally
about 65% for blowing purposes; however this is not known when
they are used for converting wind energy into electricity. They will
be used in this thesis due to their strong structure and ease of
assembly and in addition they will be needed in further studies in
the university. Due to their forward curved shape, they are
working with both drag and lift forces and to improve their
efficiency as a wind turbine, they are recommended to be used
with guide vanes.
Using a single inlet blower wheel shown in Figure.32 as first and
second ones on the left side, causes more dynamic forces on
rotating shafts because of their eccentric centre of mass to the
connection point. On the other hand, double inlet centrifugal
blower wheels indicated in the right of the Figure.32 have almost
no eccentricity in the centre of mass. Therefore, double inlet
forward curved wheels were chosen as the ideal concept.
3.4. Bearings
Figure.19 indicates the shape of the final concept of the frame, so
that bearings need to be placed as shown. The best way to do it is
57
using pillow block bearings or mounted bearings which have self
mounting abilities on the frames.
a) b)
Figure.33 a) Pedestal, and b) Pillow SKF Bearing Blocks
Figure.33 shows catalogue views of SKF Pedestal and Pillow
bearing blocks. Pedestal block bearings have cast metal housings
while pillow bock bearings only have pressed metal housings. As
the wind turbines have high vibrations and dynamic forces on
them, according high loading and rotational speed capacity of
pedestal bearings, they have been chosen for use in the final
design.
3.5. Shafts
Shafts are the easiest components to manufacture and design, so
that they were required to be designed in connection with other
components such as impellers, sliprings, frames etc. However,
their basic cross sections need to be chosen. As all the
components have inner diameter to fit on a shaft, the outer shape
of the shaft was chosen as round. Possible round shapes for
shafts can be suggested as; solid shaft and hollow shaft.
58
Figure.34 Stepped shaft concept
However, using a hollow shaft limits the possibilities of
connections and fits, so that a solid shaft which will also have
higher inertia but also higher strength will be used in the final
design. In addition, solid shaft will be machined to create steps as
shown in Figure.34 so that the bearings will be fitted easily to the
ends.
3.6. Aluminium connection for GPM12 and lower shaft
Printed DC motors were normally operated as the body fixed and
shaft was freely rotating. However, CR-VAMWT requires a freely
rotating motor body as well. Motors have some fixing holes on
them so that these holes were used to fasten them to the lower
shaft. First idea was using a C shaped thin plate as shown in
Figure.35 as red and magenta coloured parts.
Figure.35 C shape thin plate connection concept
59
C shape concept was suggested for using the least material to
reduce the weight of the connector. After suggesting C shaped
thin plate concept, the idea used with an advanced component
shown in Figure.36. In this figure, it can be seen that each C plate
had an extrusion bit to prevent relative rotation while they were
connected to the shaft which had square shape end. In addition to
this, components had holes on them for a M8 bolt with washer
which would provide tight fastening.
Figure.36 Advanced C shape cross connection concept
60
However, none of C shape concepts were used because of the
lack of manufacturing time. So that, very basic but robust concept
which was shown in Figure.37 was suggested.
Figure.37 Round cup holder concept
The material for this concept was decided as aluminium to reduce
the weight while keeping the strength at much. Also,
manufacturing of a cup was far easier than a C shaped plate as
instead of milling and drilling only turning on a lathe and drilling
would have been required.
The connection on DC motor which was shown in Figure.36 as
shaded pink colour was applied for this concept only with an
addition of dowel pin on the shaft. Due to very strong structure of
this concept, without any detailed design, technical drawing was
created on the whole wind turbine as necessary and was added to
the appendix.
61
Chapter 4. DETAILED DESIGN and
MANUFACTURING
4.1. Frame Details
Frame shape has been decided in Chapter 3 as shown in
Figure.19 however the proper dimensions had to be given
regarding the strength of the structure. Main loading cases in wind
turbine were seen as wind trust forces, weights and also rotational
dynamic loads. Moreover, the thickness of the frame should be
small to prevent high turbulent effects on wind flow as well as
occupying less space.
Figure.38 Final frame with fixings and brackets with central
distances
62
The chosen frame with fixing and brackets is given in Figure.38
has two different length of slotted profiles. Two pieces of 825mm
length and 6 pieces of 500mm length heavy aluminium profiles
with 45x45mm square cross section and 10mm slot were decided
to be used. Bracket cover caps and profile end caps were also
used to obtain better air flow but also to hide sharp ends. 45
degree brackets with fixings were suggested by the manufacturer
to be used with this profile which provides better strength for static
and dynamic loads such as bending and torsion. However, the
wind does not cause any important torsion forces over beams so
that beam calculations were done only in relation to bending
forces.
Figure.39 Chosen Aluminium frame profile drawing
Table.3 45x45H Heavy Aluminium Profile Properties[17]
Part No KJN 990 520 Profile 45x45 H
Slot Size 10 mm Mass 1.9 kg/m Moment of Inertia Ix=Iy 17.7 cm4
Section Modulus Wx =Wy 6.9 cm3 Profile Surface Area 9.2 cm2
63
Properties of the aluminium profile were given in the Table.3
which is cited from kjn aluminium profile and accessories
company website.
Maximum bending deflection of an end loaded aluminium profile
of a length of can be found by the formula suggested by Childs
were given in as follows [13] [23].
(E.2) Maximum Deflection (m),
Sym.1 F: acting static force (N)
Sym.2 L: twice the length of aluminium profile (m)
Sym.3 : Young‟s Modulus of aluminium profile (70 N/m2)
Sym.4 I: Second (area) moment of inertia (m4)
Using given properties in Table.3 for the longer aluminium profile
which had a length of 825mm, to find the required minimum force
under a maximum deflection of 1 mm, calculation was made as
following.
530N
This calculation indicates that for as small as 1mm deflection of
the end loaded longest beam requires a force of almost 530
Newton which means almost the average weight of a woman
Therefore it can easily be said that the deflection due to static
loads on the well supported beams are negligible. Normally the
forces acting over the frame and impellers due to wind are
required to be calculated, to calculate the optimal area moment of
64
inertia of the beams for individual beam parts, so that the least
material would have been used as choosing the smallest profile
cross-section.
Figure.40 500mm length 45x45H 10mm slotted aluminium profile
3D CAD drawing
4.2. GPM12 Printed DC Motor
Printed DC motors were selected from RS Components Ltd.
Company regarding their average operation speeds, dimensions
and rated power outputs which are given in PML GP Series data
sheet in the appendix. GPM12 Printed DC motor was chosen to
be used and purchased from RS Components Ltd. Company [24].
.
Figure.41 GPM12 Printed DC Motor
65
4.3. Critical speeds of rotating shafts
Eccentricity of the centre of the mass and the static deflections of
a rotating shaft creates high vibrations which can cause
catastrophic failures. „Critical speed‟ is a characteristic of any
shaft at which the high vibrations are developed. The lowest
critical speed is the main decisive property of a shaft with weights
on, which is calculated as follows [25].
(E.3)
Sym.5 etc.: weights of the rotating bodies (kg)
Sym.6 etc.: static deflections of the weights (m)
Sym.7 gravitational constant
Sym.8 critical speed (Hz)
On the other hand, a simplified approach to critical speeds of
shafts which are embedded with bearings at each end has been
given in the following equations [26].
(E.4)
Sym.9 : whirling speed
Sym.10 : 22.4 and 61.7 respectively
Sym.11 : Young‟s modulus of steel (200 GN/m2)
Sym.12 : distance between the two bearings
Sym.13 : cross sectional area (m2)
66
Sym.14 : density of the shaft (8000 kg/m3)
Sym.15 : second (area) moment of inertia of the uniform shaft
First two whirling speeds of 400mm long 25mm diameter two
bearings supported shaft was calculated as following.
Sym.16 : critical rotating speeds
As it was calculated above, critical speeds of the shaft, which
cause failure, are very high and these speeds are very unlikely to
be seen in wind turbine applications. Therefore, the shafts used
with this wind turbine were considerably fitting. Technical
drawings of shafts were given in the appendix.
4.4. Linear Tolerances
Shafts and holes usually have précised tolerances for their
diameters while their lengths have rough dimensions. This fact
occurs in order to secure the functionality of components while
reducing the cost of manufacture together with avoiding tolerance
clashes. Small tolerances result in the use of more expensive
67
tools and also increased manufacturing times. In general, during
the design of a component or even a machine, only some of the
dimensions are required to be toleranced. The rest could have a
“general tolerance” which is mostly given as ±0.5mm that
additionally decreases the time of producing the technical
drawings or sketches. The British Standard BS EN 22768
standard can be used as reference for linear dimension
tolerancing that is given in the following table. [27]
Table.4 Typical linear dimensions in BS EN 22768 standard
Dimension Tolerance
0.6 mm – 6.0 mm ± 0.1 mm
6 mm – 36 mm ± 0.2 mm
36 mm – 120 mm ± 0.3 mm
120 mm – 315 mm ± 0.5 mm
315 mm – 1000 mm ± 0.8 mm
4.5. Shaft tolerances for bearings
As it was discussed previously, holes and shafts have clear
tolerances to provide a specified function which is suggested in
BS 4500 / BS EN 20286 „ISO limits and fits‟. In this dissertation,
only necessary limits and fits tolerances are the connections of
„shafts to bearings‟ and „top shaft to DC motor shaft‟. Shaft
tolerances to be used with Y-bearings are specified by SKF
product catalogue as shown in the Table.5 . [28]
68
Table.5 20mm shaft tolerances and limiting speeds for Y-bearings
Tolerance
Grade h6 h7 h8 h9 h11
tolerances
[µm]
-13
0
0
-21
0
-33
0
-52
0
-130
Speeds
[r/min] 8500 5300 3800 1300 850
Metric equivalents of tolerance grades are given in the table as h6
for heavy loads and/or high speeds (P ≥ 0.06 C), h7 for normal
loads (P < 0.06 C), h8 for light loads and/or light speeds (P <
0.035 C), h9 and h11 for (P < 0.02 C) as shaft tolerances (P is
actual load rating and C is basic dynamic load rating which is
12.7kN for 20mm bore diameter) [28].
4.6. Tolerance calculations
4.6.1. Bearings and shafts
The tolerance for a 20mm shaft with H7 code for hole and h8 code
for shaft can be expressed as an ISO symbol with 20H7/h8 [29].
To find the exact dimensions of toleranced shafts or holes upper
and lower deviations have to be calculated. As the only
requirement for bearings is shaft tolerances to specify the correct
function, only they will be calculated in this section.
For h8 coded 20mm-diameter-shaft (20h8), maximum and
minimum basic diameter (dmax and dmin respectively) of the shaft
are calculated as follows; [29]
dmax = basic size + upper deviation
69
dmax, shaft = 20mm + 0.000mm = 20.000 mm
dmin = basic size + lower deviation
dmin, shaft = 20mm - 0.033mm = 19.967 mm
4.6.2. Top shaft hole and DC motor shaft
For 10mm shaft of the motor the hole is specified as it has an
upper deviation of 0.064mm and a lower deviation of 0.000mm
which will produce a close running fit. [29]
dmax, hole = 10mm + 0.064mm = 10.064 mm
dmin, hole = 10mm – 0.000mm = 10.000 mm
70
Chapter 5. EXPERIMENT AND TESTING
5.1. Wind Tunnel
Photograph.1 Left photo is free end, and right photo is motor
and fan part of the experiment wind tunnel
This wind tunnel shown in Photograph.1 was one of the biggest
three low speed wind tunnels in the George Begg Building wind
tunnel laboratory of the University of Manchester which could
operate up to 27 m/s of wind speed without any obstacle inside.
The air was flowing through an about 1m2 area of square shaped
corridor. The wind tunnel has a door in each side to be able to
position the experimental components. Any gaps over the corridor
were sealed to prevent air leakages which causes air pressure to
drop, so that the flowing wind‟s speed.
5.2. Finished components and assembly sequence of the
turbine
71
Photograph.2 GPM12 Printed DC motor and Aluminium cup
holder.
Photograph.3 SY20TF Plummer block bearing and SPB12
through bore 2P3S slipring
72
Photograph.4 Assembly of the turbine
Photograph.5 Shaft, centrifugal blower wheel and bearings
73
Assembly of the components was started when the frame
materials had been arrived. At first, frame was assembled with
brackets and fixings, and end covers and caps was put the slots
and gaps. Once the frame was ready, upper part of the turbine
was started to be assembled. Upper shaft was fixed to the middle
of the wheel height, and then 2 bearings were placed. After that,
the lower part was started to be assembled and before the
bearings, the slipring was assembled in place. Shaft of the DC
motor was connected to the upper shaft. While lower shaft
connected with a M8 bolt and washers, DC motor‟s cables was
pierced the aluminium cup, and then aluminium cup was fastened
to the lower shaft, and afterwards, to the DC motor, so that the
whole assembly was completed. Shafts, slipring and centrifugal
wheels had grub screws; therefore the assembly was very easy.
US+BW+BR+DC
DC motor cable through Al Cup holder CR-VAMWT
LS+BW+SR+BR+DC
Figure.42 Schematic of the assembly
Abbr.8 US: Upper shaft (machined from 1m silver steel shaft)
Abbr.9 LS: Lower shaft (machined from 1m silver steel shaft)
Abbr.10 BW: Centrifugal blower wheel (280mm Width x
280mm Height)
Abbr.11 BR: SY20TF Bearings
Abbr.12 SR: SPB12-2P3S Slipring
Abbr.13 DC: GPM12 Printed DC motor
74
5.3. Experimental Setup
Experimental rig were designed as shown in Figure.43 that we
were able to record the generated amperes and voltages over the
wind turbine. The light bulb needed to be used to complete the
circuit as a resistor (or load) which creates the voltage difference.
Figure.43 Wind generator experimental circuit with 100W light
bulb , ammeter (A), and voltmeter (V)
After designing all the circuits and wind generator, the CR-
VAMWT was placed inside the wind tunnel and placed in the
middle of the cross-section of the corridor. The machine was
about 32kg so that the friction between the wood of the base of
the tunnel was thought enough to hold the turbine in place which
is shown in Photograph.6 , therefore, no bolt connection was
necessary to fix it. Also, the power cables were taken out of the
tunnel through circular hole on the wooden basement. Slipring
was fixed to the frame using plastic locking straps which were also
used to fix impellers.
75
Figure.44 Final CAD Design
Voltmeter and ammeter was placed on a table next to the wind
tunnel and very close to the wind turbine to reduce the length of
the cables. Additionally, a piezometer which estimates the wind
pressure shown in a pressure gauge was placed on the wind
76
tunnel. This component was also recording the wind speed inside
the tunnel.
Photograph.6 CR-VAMWT inside the wind tunnel; model (left)
and real (right)
Photograph.7 Ammeter with bulb (left), and voltmeter (right)
77
Experiment was done to show the benefits of using a counter
rotating wind turbine which has freely rotating generator. Tests
were done in three different cases, such as;
Case1: Both impellers were freely rotating
Case2: Lower impeller was fixed
Case3: Upper impeller was fixed
5.4. Gathered Data
5.4.1. Case 1: Both impellers were freely rotating
In this case, impellers were rotating freely with the printed DC
motor‟s body and its shaft. Power generation was started to
record at 10m/s wind speed as shown in Table.6
Table.6 Both propellers rotating:
Speed (m/s)
Voltage (V)
Current (A)
Power (W)
10 2.6 0.452 1.1752
11 2.95 0.465 1.37175
12 4 0.52 2.08
12.5 4.23 0.537 2.27151
13.5 5 0.567 2.835
13.8 5.42 0.592 3.20864
From the Table.6 and Diagram.5 it can be seen that while the
generated amperes increasing very slightly, the generated voltage
increases with wind speed. While during 10m/s wind speed only
1.18W power generated, for 13.8m/s it was seen as 3.2W. Almost
a quarter much increase in wind speed caused to produce almost
trebled power output from the wind turbine.
78
Diagram.5 Generated voltage, ampere and power with
respect to the wind speed for Case1
Table.7 Upper impeller rotating (lower propeller restrained):
Speed (m/s)
Voltage (V)
Current (A)
Power (W)
8 0.23 0.172 0.03956
10 0.54 0.255 0.1377
10.5 0.69 0.27 0.1863
11 0.83 0.3 0.249
11.6 1.05 0.322 0.3381
12.2 1.34 0.348 0.46632
12.8 1.58 0.365 0.5767
Table.7 and Diagram.6 represents the data obtained from only
free upper impeller. As the upper shaft was only carrying tone of
the impeller and GPM12 motor‟s shaft, its inertia was very less
than the lower shaft which was also carrying slipring, GPM12
Motor‟s body and the aluminium cup holder.
00.5
11.5
22.5
33.5
44.5
55.5
6
10 10.5 11 11.5 12 12.5 13 13.5 14
Wind Speed (m/s)
Both impellers rotating
Voltage (V) Current (A) Power (W)
79
Diagram.6 Generated voltage, ampere and power with
respect to the wind speed for Case2
If 10m/s wind speed was taken as a comparison speed, power
output was almost dropped to 12% of both impellers‟ power
output.
Table.8 Lower impeller rotating (upper impeller restrained)
Speed (m/s)
Voltage (V)
Current (A)
Power (W)
6 0.04 0.03 0.0012
7 0.06 0.047 0.00282
8 0.12 0.078 0.00936
8.5 0.14 0.092 0.01288
9 0.18 0.11 0.0198
9.5 0.23 0.135 0.03105
10 0.29 0.166 0.04814
10.5 0.38 0.199 0.07562
10.8 0.46 0.22 0.1012
11 0.52 0.234 0.12168
0
0.5
1
1.5
2
8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13
Wind Speed (m/s)
Lower impeller fixed
Voltage (V) Current (A) Power (W)
80
In Case 3, upper impeller was fixed, so that only lower impeller
could contribute to the power production. Again according to
10m/s wind speed, power output was seen as 0.048W which is
about 35% of the power output for the same wind speed in Case2.
Diagram.7 Generated voltage, ampere and power with
respect to the wind speed for Case3
When we summed the two separate power outputs for 10m/s wind
speed it was seen that total power production was 0.18584W.
However, when both of the impellers were free to rotate in Case1,
the power output was recorded as 1.1752W which was about 6
times higher than the total power output of Case2 and Case3.
0
0.1
0.2
0.3
0.4
0.5
0.6
6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11
Wind Speed (m/s)
Upper impeller fixed
Voltage (V) Current (A) Power (W)
81
Chapter 6. DEVELOPMENT OF THE DESIGN
6.1. Calculations for Energy Production
Air Density Blade Height
Wind Speed
Blade Width
Number of Turbines
Turbine Swept Area
Theoretical Power
Efficiency
Theoretical Generated Power
Annual Production Estimation for a Recent Design
Annual Production Requirement Estimation
Power Generation Requirement Estimation
Area Required
HAWT Rotor diameter
VAWT Rotor width and height
1.2kg
m3
b 280mm 0.28 m
Vw 24mph 10.729m
s
d 650mm 0.65 m
n 1
At n d
2
2
0.332m2
P1
2 Vw
3 At 245.89W
ef16
2755 % 32.593 %
Px ef P 80.142 W
Pr 2572kW hr
yr293.413W
Preq Pr 4 1.029 104
kW hr
yr
Preqa Preq 1.174 103
W
Vs 7m
s Areq Preq 2
1
ef Vs3
17.497m2
rdAreq
m5.57m
rw3
Areq m 2.596m
rhAreq
rw6.74 m
82
Previous Mathcad codes were generated to calculate and
estimate the required area of a horizontal and vertical axis wind
turbine to provide enough annual power for a single house.
Ideally while there was 24mph wind speed, a horizontal axis wind
turbine with a diameter of 0,65m can generate up to 246W.
However, due to Betz Limit and the frictions, the efficiency of the
turbine was estimated as 32.593% so that the maximum
generated power can be up to 80W.
In addition, if the annual production requirement was estimated as
1.174kW, and the average wind speed of the area was 7m/s, then
the required area can be calculated as 17.479m2. Horizontal axis
wind turbines have only a circular area to cover this area which
results a rotor diameter of 5.57m. And if a vertical axis wind
turbine was suggested to use a width of cubic root of that area,
then the width and height of the required cross section of impeller
can be found as 2.596m and 6.74m respectively.
6.2. Computer Aided Design of Concepts Using Solidworks
While designing in Solidworks platform, one can start with a really
basic shape such as a circle or rectangle. One of the best parts of
CAD designing is the ability to play with the numbers and get the
results in seconds. Using 3D views one can see the most
unpredictable interceptions but also to produce new design ideas.
The ability to see section views, dimensions, mass properties or
even calculation of the center of mass provides valuable
information to create new concepts. Also using toolboxes or
downloading CAD drawings of the products makes the design
easier. Using different colours on different parts increases the
83
perception and discretion so that explaining the ideas to any other
person becomes much easier.
6.3. Finite Element Analysis Using Abaqus CAE
ABAQUS CAE programme was used to estimate the critical
speeds of the shafts considering they were one. Dimensions of
the model were the same as the real components dimensions
which can be found in the Appendix.
a) b) c)
Figure.45 a) solid shaft model with bearings, wheels and
generator; b) boundary conditions; c) meshed part
84
Boundary was applied over extruded bearing places as pinned
(U1=U2=U3=0) boundaries. Properties of the steel was chosen as
density 7850 kg/m3, Young‟s Modulus E=205x109 N/m2, and
Poisson‟s ratio 0.29.
Part was designed in Solidworks and imported into Abaqus CAE
platform to perform the analysis. After importing the file, material
properties were added and an independent assembly was used.
Under the step module, a standard general step was created and
procedure type was chosen as “linear perturbation” to find out
natural frequencies. “U, translations and rotations” was chosen as
field output. Under load module, a pinned (U1=U2=U3=0)
boundary condition was created without any load. Mesh model
was selected and mesh controls were applies as; Element type:
Tet, Technique: Free, Algorithm: Default. C3D10M type element
was used from standard element library and with a quadratic
geometric order. From the performed analysis, the following data
was recorded in Table.9 .
Table.9 First 10 natural frequencies of Abaqus model
MODE FREQ [Hz]
RPM
1 14.6824 880.944 2 14.6911 881.466
3 14.8158 888.948
4 14.8209 889.254
5 19.2202 1153.212
6 19.2209 1153.254 7 40.3999 2423.994
8 51.0281 3061.686 9 51.0465 3062.79
10 51.3087 3078.522
85
These frequencies were needed to be passed fast during the
operation of the wind turbine to prevent failure of the shaft.
Figure.46 Mesh on the wheel models (left) and mesh on the DC
motor models (right)
It can be said that failures due to shafts were unlikely if operating
speeds of the turbine were different to those in Table.9
Figure.47 Boundary conditions on meshed bearing place
86
Figure.48 First 10 deformation of mode shapes from top left to
bottom right respectively
87
Chapter 7. DISCUSSIONS, FUTURE WORK AND
CONCLUSIONS
7.1. Discussions on the outcomes
The experiment results showed that, using a counter rotating wind
turbine with a freely rotating generator can produce higher
amounts of power than common wind generators. Even though
the power output of CR-VAMWT was 6 times higher than the total
of the two separate wheels‟ power outputs it has to be due to the
power curve of the generator which indicates that increasing
rotation speeds the output increases drastically in the beginning.
However, we couldn‟t reach the design speed of the generator
which would have given us better information as it was assumed
that the speed increase in the motor with counter rotating ability
would be only two times less than if we had had single ones.
Therefore the power output could be estimated proportional to that
ratio.
The power output of the wind turbine was seen as too low. This
result could have been caused by wrongly applying impellers
which normally work to create centrifugal forces on the air to push
it through ducts. Perhaps providing guide vanes would improve
the outcome of this wind generator.
Abacus CAE programme results indicated the possible loading
shapes and also the critical loading areas on shafts, wheels,
generator and also bearings. A more detailed design of the shaft
according to these loading shapes would have been created to
choose the cheapest but sufficiently strong structure of the shafts.
88
Solidworks programme provided the designer with a high vision of
the concepts, so that, every time the concepts were taken to an
advanced stage. To manage the time of the project, when the
necessary parts were obtained, the concept design was
concluded. In addition, it was understood that, each concept
should have been saved completely in separate folders, and also
each component should have been presented in different colours
in each concept.
Bending load calculations for the frame indicated that the chosen
frame was too strong. In addition, the aluminium cup was
designed as to be unnecessarily sturdy to eliminate any assembly
errors. The blower wheels were made of galvanized steel which
has a huge amount of inertia with respect to composite materials
or even the aluminium.
7.2. Future works
We hope this study would lead to further research on the subject
of counter rotating wind turbines. The effects of counter rotating
impellers over motor bodies should be investigated as they will be
subject to high vibrations. In addition, the necessity of gear sets to
increase the relative shaft speed should be taken into account.
Maybe planetary gear sets with a fixed ring gear with sun and at
least three planet gears could be suggested to increase the
speeds. Also if the planet gear could be correctly mounted, then
the two middle bearing would be eliminated, which would
decrease the cost. As it was suggested in Figure.31 the benefits
of articulated vertical axis blades with small Savonius blade
concept should be tested in a counter rotating wind turbine
concept using planet gears. Also, golden ratio (1.618) rules could
89
be applied to generate better looking counter rotating wind
turbines which was shown in Figure.49.
Figure.49 Golden design of the frame
However, instead of this very robust frame a basic frame which
would not interfere with the wind flow should be generated to
reduce the turbulence.
Furthermore, an analysis for integrating micro wind turbines to the
buildings should be made.
7.3. Conclusions
In this study, a counter rotating vertical axis wind turbine was
designed using Solidworks, Mathcad and Abaqus CAE programs.
The importance of using CAD software for the aim of designing a
90
machine was experienced. The importance of tolerancing in
manufacture is experienced with the help of CAD software. The
benefits of CR-VAMWTs over single rotating impeller wind
turbines were found as high as six times of the output for low
efficiencies. It should also be investigated for motors and
impellers which are operating in optimal speeds.
Siting of the micro wind turbines, is one of the most important
factors in obtaining better power outputs due to changing wind
flow over obstacles. So that a micro wind turbine should be put on
the roof of a building with an enough height of tower. Also to
acquire enough source of power to a residence or a building,
Because of the small power generation of the micro wind turbines,
an array of them should be considered to use. Moreover,
according to increasing demand in electricity, new building should
have been built regarding to possible micro wind turbine
integration facilities such as suitable concrete structures or self
towers.
91
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APPENDIX
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