design and analysis of an airfoil for small wind turbines
DESCRIPTION
Designing of a suitable airfoil or aerofoil and winglet for the small wind turbines by using the Computational Fluid Dynamics software. The values are also compared to the realtime expermentation.TRANSCRIPT
DESIGN AND ANALYSIS OF AN AIRFOIL
AND WINGLET FOR SMALL WIND
TURBINES
A PROJECT REPORT
Submitted by
ELANGO.N 090111139011
VIGNESHKUMARAN.C 090111139053
ARAVINDKUMAR.N 100411139001
in partial fulfillment for the award of the degree
of
BACHELOR OF ENGINEERING
in
MECHANICAL ENGINEERING
P. A. COLLEGE OF ENGINEERING AND TECHNOLOGY, POLLACHI - 642 002
ANNA UNIVERSITY: CHENNAI 600 025 APRIL 2013
BONAFIDE CERTIFICATE
Certified that this project report “DESIGN AND ANALYSIS OF AN
AIRFOIL AND WINGLET FOR SMALL WIND TURBINES” is the bonafide
work of N.ELANGO (090111139011), C.VIGNESHKUMARAN (090111139053),
and N.ARAVINDKUMAR (100411139001) who carried out the project work under
my supervision.
SIGNATURE SIGNATURE
HEAD OF THE DEPARTMENT SUPERVISOR
Mr. P.T.SARAVANAKUMAR.M.E.,(Ph.D)., Mr. V.P.SURESHKUMAR.M.E.,M.I.S.T.E.,
Head of the department, Assistant professor,
Department of Mechanical Engineering, Department of Mechanical Engineering,
P. A. College of Engineering & Tech, P.A. College of Engineering & Tech,
Pollachi- 642002. Pollachi - 642002.
INTERNAL EXAMINER EXTERNAL EXAMINER
i
ACKNOWLEDGEMENT
With genuine humility, we are obediently thankful to God Almighty praise and
glory is to Him, for all His uncountable bounties and guidance, without which, this work
would have never been a reality.
We express our profound gratitude to our respected Chairman
Prof.P.Appukutty,M.E.,FIV. for giving this opportunity to pursue this course.
At this pleasing moment of having successfully completed the project work, we
wish to acknowledge our sincere gratitude and heartfelt thanks to our respected Principal
Dr.T.Manigandan,M.E.,Ph.D., for having given us the adequate support and opportunity for
completing this project work successfully.
We express our deep sense of gratitude and sincere thanks to Mr.P.T.Saravana
Kumar,M.E.,(Ph.D)., Head of the Department, who has been a spark for enlightening our
knowledge.
We express our deep and sincere thanks to Dr. V. Ramalingam., M.E.,Ph.D.,
Dean of Mechanical Department, who has been a spark for enlightening our knowledge.
Our profound gratitude to project co coordinators Mr.N.Gnanaseker,M.E.,
Assistant Professor and Mr.K.Manikandan,M.E., Assistant Professor of Mechanical
Department for their valuable guidance and generous help.
We express our deepest, heartiest and sincere thanks to our project guide
Mr.V.P.Suresh Kumar,M.E.,M.I.S.T.E., Assistant Professor of Mechanical Department, for
her valuable guidance throughout my work during the entire course of the work. We extend
our deep thanks to all staff members of Mechanical Department for their help and assistance
during the project.
We express our deepest, heartiest and sincere thanks to Mr. S. K. Shreenivas,
M.E., (Ph.D)., Mr. M.Sathishkumar,B.E., and all the technical persons of KST WIND
ENGINEERING INDIA, for their guidance and motivation in my project work.
Our humble gratitude and heartiest thanks goes to our family members and friends
for their encouragement and support throughout the course of this project.
ii
ABSTRACT
The ultimate objective of the project is to increase the reliability of wind
turbine blades through the development of the airfoil structure and also to reduce
the noise produced during the running period of the wind turbine blades. The
blade plays a pivotal role, because it is the most important part of the energy
absorption system. Consequently, the blade has to be designed carefully to
enable to absorb energy with its greatest efficiency. In this project work, Pro E,
Hypermesh and CFD software has been used to design blades effectively.
NACA 63-215 airfoil profile is considered for analysis of wind turbine blade.
The wind turbine blade is modeled and several sections are created from root to
tip with the variation from the standard design for improving the efficiency. For
the further improvement required in the efficiency of the wind turbine the
winglet is to be included at the tip of the blade which would help in increasing
the efficiency and reducing the noise produced from the blades in working
condition. The existing turbine blade and the modified blade with the winglet
are compared for their results.
iii
TABLE OF CONTENTS
CHAPTER
NO. TITLE
PAGE
NO.
Abstract ii
List of figures v
List of abbreviations vi
1 INTRODUCTION 1 - 7
1.1 Introduction 1
1.2 Yesteryear Design 3
1.3 Contemporary Design 4
2 LITERATURE REVIEW 8 – 10
3 AIRFOILS IN WIND TURBINE
APPLICATION 11 - 18
3.1 Introduction 11
3.2 Airfoil Terminology and Classification 11
3.3 Forces acting on Airfoils 13
3.4 Aerodynamics of Airfoils 13
3.5 Airfoil Database 15
3.6 Airfoil cl and cd Data Interpolation and
Extrapolation 17
iv
4 PROBLEM IDENTIFICATION 19
5 OBJECTIVE 20
6 DESIGN CONSIDERATIONS 21 - 38
6.1 Airfoils and Blade Geometry 21
6.2 Winglet Design 22
6.3 Design Components 24
6.4 Theoretical Design 25
6.4.1 Blade Pitch Angle 25
6.4.2 Blade Twist Angle 26
6.4.3 Chord Distribution 26
6.4.4 Proposed initial design 26
6.5 Final Design with Winglet 36
6.5.1 Sizing and Parameters 36
6.5.2 Cant Angle 37
6.5.3 Radius (Percentage of Height) 37
6.5.4 Height 37
6.6 Final CAD Design 37
7 ANALYSIS 39 - 48
7.1 Boundary Conditions 40
7.1.1 Velocity Inlet 40
7.1.2 Pressure Outlet 41
7.1.3 No Slip wall 43
v
7.1.4 Periodic condition 43
7.1.5 Symmetry 43
7.2 Solution Method 43
8 MANUFACTURE OF BLADE 49 - 58
8.1 Overview of Production Procedure 49
8.2 Basic Design 50
8.3 Equipments Required 50
8.4 Materials and Chemicals Required 51
8.4.1 Resin 51
8.4.2 Resin Type ‘R10-03’ 51
8.4.3 Resin Type ‘Polymer 31-441’ 51
8.4.4 Styrene monomer 52
8.4.5 Hardener 52
8.4.6 Dura wax 52
8.4.7 Chopped Strand Fiber glass mat (CSM) 53
8.4.8 Woven Cloth Fiber glass (WC) 53
8.4.9 Thinners 53
8.4.10 Wooden Core Roots 54
8.5 Tools Required 54
8.6 Half Blade Manufacture 55
8.7 Blade Joining 56
8.8 Blade Finishing 56
vi
9 TESTING & VALIDATION 58 - 65
9.1 Testing Conditions 58
9.2 Plane blade testing 59
9.3 Winglet blade testing 60
9.4 Validation 61
9.4.1 Voltage vs. Wind Speed 61
9.4.2 Current vs. Wind Speed 62
9.4.3 Noise Level 64
10 CONCLUSION 66 - 67
PHOTOGRAPHS 68 – 69
APPENDICES 70 - 72
REFERENCES 73 - 74
vii
LIST OF TABLES
TABLE
NO.
TITLE PAGE
NO.
3.1 Airfoil families used in airfoil database 16
6.1 Airfoils for blade design 28
6.2 Position of airfoils along length of the blade 28
6.3 Parameters for blade design 29
6.4 Airfoil Station Distribution for Final Blade Design 39
6.5 Airfoil Configuration 39
6.6 Final Winglet Parameters 39
7.1 Assigned Boundary Conditions 44
9.1 Testing Conditions 59
9.2 Voltage and Current value for Plane blade 60
9.3 Voltage and Current value for Winglet blade 61
viii
LIST OF FIGURES
FIGURE
NO.
TITLE PAGE
NO.
1.1 Coriolis Force 2
1.2 Flow of Wind and Currents across the Globe 2
1.3 Smock Mill Wind Turbines 3
1.4 Rotor Diameters vs. Years 4
1.5 Siemens SWT-6.0 Wind Turbine 6
3.1 Basic airfoil parameters 11
3.2 Example for different thickness distributions in
two airfoils
12
3.3 DU airfoil family 13
3.4 Definition of forces 13
3.5 Airfoil data interpolation for angle of attack results
compared with originals
17
3.6 Airfoil data interpolation for Reynolds number
results compared with originals
17
3.7 Airfoil data interpolation for Reynolds number
results compared with originals
18
6.1 Blade profiles from NACA 63-430 and NACA 63-
215
21
6.2 Parameters describing winglet geometry 23
6.3 Winglets with different sweep angles 23
6.4 Winglets with different height 24
6.5 Sections of blade 29
6.6 2D Airfoil in Pro Engineer 29
ix
6.7 Curves in blade 30
6.8 Airfoil twist in blade 30
6.9 Isometric view of Finalized Normal blade 31
6.10 Winglet design 31
6.11 Winglet geometry in Pro Engineer 32
6.12 Winglet blade final design – Isometric view 32
6.13 Winglet blade with hub 33
6.14 Isometric view of hub 33
6.15 Isometric view of nose 34
6.16 Isometric view of nacelle 34
6.17 Isometric view of tower 35
6.18 Assembled view of Present design 35
6.19 Assembled view of new design (Winglet) 36
7.1 Meshed Wind Turbine Assembly with boundary 39
7.2 Inlet and Outlet of the boundary 40
7.3 Imported parts in Hypermesh 41
7.4 Meshed part in Hypermesh 41
7.5 Meshed Nose and Hub 42
7.6 Meshed Winglet 42
7.7 Iterations for Wind speed 2.0 m/s 44
7.8 Static Pressure for Wind speed 2.0 m/s 45
7.9 Velocity Magnitude for Wind speed 2.0 m/s 45
7.10 Iterations for Wind speed 3.0 m/s 46
7.11 Static Pressure for Wind speed 3.0 m/s 46
7.12 Velocity Magnitude for Wind speed 3.0 m/s 47
7.13 Iterations for Wind speed 4.0 m/s 47
7.14 Static Pressure for Wind speed 4.0 m/s 48
7.15 Velocity Magnitude for Wind speed 4.0 m/s 48
x
8.1 Two equal halves of blade 50
8.2 Resin Type ‘R 10-03’ 51
8.3 Resin Type ‘Polymer 31-441’ 51
8.4 Hardener 52
8.5 Dura wax 52
8.6 Woven Cloth Fiber Glass 53
8.7 Wooden core root 54
8.8 Safety Equipments 54
9.1 Efficiency Calculation for Winglet Blade 61
9.2 Wind speed vs. Voltage (3 phase) – Plane blade 61
9.3 Wind speed vs. Voltage (3 phase) – Winglet blade 62
9.4 Wind speed vs. Ampere (3 phase) – Plane blade 63
9.5 Wind speed vs. Ampere (3 phase) – Winglet blade 63
9.6 Waveform for noise in Plane Blade 64
9.7 Noise level graphs for Plane Blade 64
9.8 Waveform for noise in Winglet Blade 65
9.9 Noise level graphs for Winglet Blade 65
xi
LIST OF ABBREVIATIONS
NACA - National Advisory Committee of Aeronautics
BEM - Blade Element Momentum
NREL - National Renewable Energy Laboratory
NASA - National Aeronautics and Space Administration
DU - Delft University
DC - Direct Current
HAWT - Horizontal Axis Wind Turbine
VAWT - Vertical Axis Wind Turbine
RPM - Revolution per Minute
kVA - Kilo Volt-Ampere
MVA - Mega Volt-Ampere
MW - Mega Watt
KW - Kilo Watt
PFC - Power Factor Correction
CAD - Computer Aided Design
CFD - Computation Fluid Dynamics
CSM - Chopped Strand Fiber Glass Mat
WC - Woven Cloth Fiber Glass
2D - Two Dimensional
3D - Three Dimensional
Cl - Co efficient of lift
Cd - Co efficient of drag
db - Decibel
Cm - Moment Coefficient
Tsr - Tip Speed Ratio
SWT - Siemens Wind Turbine
xii
KWh - Kilo Watt Hour
U - Velocity of air
L - Reference length
ρ - Fluid density
µ - Dynamic viscosity
υ - Kinematic viscosity
λr - Local speed ratio
φ - Blade twist angle
α - Angle of attack
B - Number of blades
1
CHAPTER 1
INTRODUCTION
The need for electricity in our generation is of prime importance due to the sort
of evolved life mankind leads. The production of power using traditional methods has
taken its toll on the environment and the earth has been polluted to degrees beyond
imagination. Alternative energy and green energy from natural recourses is the need
of the hour. Technology must be used so as to provide human need and luxuries but
still not affect our planet. With increasing awareness about our needs and priorities
one alternative source where we can draw power would be the wind.
Wind is such a resource available that it just blows everywhere, from large
areas to local winds it just blows. There are various phenomenons that occur that
makes the flow of wind across the globe. Wind blows along the planet due to the
difference in temperatures across the surface of earth, the hot air rises up and cool air
rushes to fill up the void. The equatorial region of the earth gets heated up and in turn
heats the air above it causing the wind to blow higher due to which pressure drops and
the air that’s cooler near to the poles rush towards the equator, called the Geotropic
Wind. This occurs at higher altitudes of the atmosphere. There is a Coriolis force due
to the rotation of the earth, the northern hemisphere the winds move counter
clockwise and the southern hemisphere it rotates clockwise figure 1.1 shows this
effect. Surface winds are affected by the obstacles on the earth up to a height of 100
meters. There are winds called sea breeze and land breeze which can also be a source
of wind power generation.
The local winds are also influenced by the global and local effects, the
landscape of the region. The seasonal winds change take places in South Asia. The
winds around mountain regions due to the pressure differences and the height of the
2
hills make up for these kinds of winds that are strong. Something that is so freely
available in nature is a source where enormous power can be harnessed and used. The
clean, inexhaustible, constant everyday occurrence and green energy part of this
source is the essence why we need to choose as a part of our large consumption of
energy needs.
Figure 1.1 Coriolis Force
Figure 1.2 Flow of Wind and Currents across the Globe
3
The power of wind is harnessed completely can actually power a whole nation,
and if used with other natural alternative energy we can create a pollution free green
environment. This energy is so important to third world countries where basic
electricity is not available. Power of wind turbines has increased 100 times compared
to the wind mills those existed a couple of decades ago.
1.2 YESTERYEAR DESIGN
A brief history goes on to show that harnessing wind energy was done for a
variety of purposes in as early as 7th century. The use of wind energy in getting water
out of wells and grinding was a part where this source was of great significance for
free power. Older wind capturing machines developed in 200 BC is considered to be
the first instance where wind was as a power source for machines. The European
countries had built smock mill type of turbines which was mainly used for drawing
water from wells and for agricultural purpose, figure 1.3.
Figure 1.3 Smock Mill Wind Turbines
4
In order to harness the wind effectively and for the low costs, the advancement
of technology over the last few decades has given rise to not individual turbines but
wind farms in general. Advances in materials and composites used for construction of
turbines, the analysis for efficiency of aerodynamics and structures, accurate
prediction of winds and their direction have provided for cost effective production of
power. As technology in every area is advancing the turbines go higher and grow
powerful. As Greenpeace international puts it, “Behind the tall, slender towers and
steadily turning blades lays a complex interplay of lightweight materials, aerodynamic
design and computer controlled electronics”.
1.3 CONTEMPORARY DESIGN
As wind turbines go higher and wider, these can be used only at certain places.
The usage of wind turbine in wind farms are of each producing 1.5 MW and around
60-80 meters in length. Figure 1.4 gives an approximate rotor diameter and years in
production.
Figure 1.4 Rotor Diameters vs. Years
5
The modern type wind turbine was produced by Siemens, figure 1.5 was the
first built 6.0 MW in the year 2010. HAWT are of various types depending on the
number of blades ranging from one blade to any odd number of blades. The three
bladed rotors are the most industry accepted design and version. The largest wind
turbine today is the ‘Siemens SWT-6.0’ figure 1.5, which produces an excess of 6.0
MW of power producing about 20 million KWh per year.
The aerodynamic efficiency is lower on a two bladed rotor compared to a three
bladed rotor, the rotation speed needs to be higher so as to achieve the same power as
that of the three bladed rotor. The two and single bladed rotors need a special kind of
arrangement that is hinged or teetering hub. Each time the rotor passes the tower and
in order to avoid heavy shocks the rotor is to tilt away. Also the arrangement can have
balance issues and in time the blades are bound to hit the tower during operation. The
three bladed rotors are effective to use the yawing mechanism in them.
Analysis of blades using wind tunnel would be possible for small scale rotors,
but the increase in diameters has called for the use of Computational Fluid Dynamics
for fluid flow over blades and prediction of loads.
The current energy needs of man are dependent on carbon based fuels that are
cheap and easily accessible, but the limitation and the environmental effects it has
staggeringly improvised the need for alternate cleaner energy. The advancement of
technology and the greener energy needed for the luxuries of mankind are the prime
reason for this report and also the advancements as seen from figure 1.5.
6
Figure 1.5 Siemens SWT-6.0 Wind Turbine
For the use of alternative sources of energy, we need to bring in more laws and
the promotion of this is definitely an added advantage considering what natural
calamities can do to power plants that are dangerous as in the case of nuclear energy
or the dangers of burning coal and exhausting the reserves of carbon based fuel. It
takes commitment and action on part of all of human kind for promoting these
energies.
In order to produce larger wind turbines the efficiency of the blades designed
must be optimum. Since turbines growing larger in diameter, the rotation speed is
slow and hence power production is dependent on high performing aerodynamic
design, a rigid structure, advanced composite materials and optimization techniques to
maximize power minimize cost of production are of importance and to be
scientifically studied and implemented.
7
There is no perfect rotor design, the choice of parameters are just optimized to
obtain one of a kind of rotor, the different airfoils and the choice of material with the
speed of rotation and the wind speeds for which the turbine is designed just leads an
understanding that optimization is critical in the design phase of the wind turbine
rotors.
In order to produce power efficiently medium scale turbines that are of 1 MW
to 5 MW capacities are designed. In order to be efficient in drawing power from the
wind optimization techniques are needed at various stages in design of the rotors to
the arrangement of the turbines in the wind farms is of importance.
A survey of literatures for this thesis has yielded that result for blades of
lengths of well between 1 to 3 meters has been optimized for maximizing power and
decreasing the weight of the blades. The blades of length greater than 2 meters has a
different design concept and the usage of CFD is needed for optimizing
aerodynamically and the structures of the blades are very different. In most cases the
small turbines are scaled dimensionally for designing medium scale turbines, hence
an initial estimate of how designing and optimizing of a medium scale turbine from
beginning forms the basics of the small wind turbine blades which is carried out in
this work.
8
CHAPTER -2
LITERATURE REVIEW
A significant amount of exhaustive research has been done in the area of
small and medium scale wind turbine blades and most of them have used the
classical blade element momentum theory for designing the blades and calculating
the forces acting on it. Lot of research on finding the optimum chord lengths has
been made using a variety of evolutionary optimizing techniques. Some work that
forms the background for this research is as follows.
Jackson, et.al made a preliminary design of a 50 meters long blade, two
versions one of fiber glass and one with carbon composite was used to test the cost
and thickness of cross sections was changed in order to improve structural
efficiency. The aerodynamic performance was made using computational techniques
and the computations were predicted using clean and soiled surface.
Karam and Hani optimized using the variables as cross section area, radius of
gyration and the chord length, the optimal design is for maximum natural frequency.
The optimization is done using multi dimensional search techniques. The results had
shown the technique was efficient.
K.J. Johansen, and Sørensen, N.N modified the tip of the rotors to winglet to
improve the aerodynamic performance of turbine rotors and to make them less
sensitive to wind gusts.
Maughmer, M.D tilted the blade tip to the effect of winglets which decreases
the induced drag of the blade by changing the downwash distribution, hence
increasing the power production.
9
Mickael Edon had designed a blade for 38 meters for a 1.5MW power using
the BEM theory, and had suggested in his future work the chord distribution formula
which I have implemented. Since his blade was close to my design I choose the
same airfoil profile.
M. Jureczko, M. Pawlak, A. Mezyk used the BEM theory to design and used
ANSYS for calculation of natural frequencies. They had found out the mode shape
of the blades by using the Timoshenko twisted tapered beam element theory. The
genetic algorithm was used to minimize blade vibration, maximize output, minimize
blade cost and increase stability.
Philippe Giguere and Selig had described blade geometry optimization for
the design of wind turbine rotors, pre-programmed software was used to optimize
structures and cost model.
Tingting Guo, Dianwen Wu, Jihui Xu, Shaohua Li developed a 1.5 MW
turbine rotor of 35 meters blade length, using Matlab programming for designing
and concluded the feasibility of Matlab for designing large wind turbines, further
they had also compared with CFD results and the found out Matlab was economical
in artificial design and optimizing for efficiency.
Wang Xudong, et al used three different wind turbine sizes in order to
optimize the cost based on maximizing the annual energy production for particular
turbines at a general site. In their research using a refined BEM theory, an
optimization model for wind turbines based on structural dynamics of blades and
minimizes the cost of energy. Effective reduction of the optimization was
documented.
Z.L. Mahri and Rouabah had calculated the dynamic stresses on a blade
which was designed using the blade element theory. The rotor diameter was 10
10
meters and the dynamic analysis was made using the beam theory and the modal
analysis is made using the finite element modeling and also using the blade motion
equation.
This present work is done in designing a wind turbine blade using the Blade
Element Theory for a length of 1.5 meters which is suitable for 2.0 KW small wind
turbine. The chord lengths are calculated and the chord distributions, flow angles,
the differential power, thrust and torque are all at discrete intervals of the blade are
plotted. The blade is then assumed to be a tapered hollow beam. The natural
frequency is found out by solving the Eigen value problem. The blade efficiency can
be increased by attaching a winglet to the end of the blade. The winglets are
normally used in the aerospace vehicle designs.
11
CHAPTER 3
AIRFOILS IN WIND TURBINE APPLICATION
3.1 INTRODUCTION
Airfoils generate the aerodynamic forces on a wind turbine blade. Power of a
wind turbine is related to aerodynamic and geometrical properties of its airfoils.
Airfoil properties such as aerodynamic forces which are lift and drag produced by
airfoils of a wind turbine blade has to be known in order to achieve desired
performance. In this chapter, main characteristics and properties of airfoils will be
revisited.
3.2 AIRFOIL TERMINOLOGY AND CLASSIFICATION
Geometrical parameters defining an airfoil are shown in Figure 3.1 below.
Figure 3.1 Basic airfoil parameters
Most of the time, dimensions related with airfoils are given as referenced to
the chord length. Thickness of an airfoil is usually represented with maximum
12
thickness percentage of the airfoil related to chord. Camber of an airfoil also has a
similar definition: it is represented by maximum camber percentage related to chord.
From structural point of view, thickness and camber distribution is very
important. Airfoils may have the same thickness or camber values but different
distributions. This is shown in Figure 3.2. Both airfoils have similar thickness and
camber values. However, since the distributions are different, these airfoils cannot
be used at the same time for the same wind turbine blade. Therefore, different
airfoils have to have some common characteristics in order to be used together on a
wind turbine blade.
Figure 3.2 Example for different thickness distributions in two airfoils.
Airfoils that have similar thickness or camber characteristics are produced for
this purpose. These airfoils are called airfoil families or airfoil series. Most famous
airfoil families are produced by NACA. The examples of NACA airfoil families
which are used also in wind turbine applications are NACA 63, NACA 64 and
NACA 65 airfoil families. In addition to NACA airfoils, there are several airfoil
families developed by European and US research institutes for wind turbine
applications. For example, Risoe-A1, A2 or Risoe-B1 airfoil families which are
designed by Risoe National Laboratory in Denmark. Other famous airfoil families
are developed by Delft University in Netherlands which are called as DU airfoil
families. An example of DU airfoil families is shown in Figure 3.3.
13
Figure 3.3 DU airfoil family
NREL (National Renewable Energy Laboratory) in US also developed airfoil
families which are called as NREL S-series airfoils. There are several other airfoils
developed and used in wind turbine applications. In almost all of the airfoil families
produced for wind turbines, structural concerns are included in airfoil design .
3.3 FORCES ACTING ON AIRFOILS
Figure 3.4 Definition of forces
The reacting force F from the flow is decomposed into a direction
perpendicular to the velocity of fluid and to a direction parallel to fluid. The former
component is known as the lift, L; the latter is called the drag, D
3.4 AERODYNAMICS OF AIRFOILS
Flow over an airfoil creates distributed force on the airfoil. When the flow
passes over the upper or convex side of the airfoil, flow velocity increases which
14
decreases the pressure acting on the surface. On the other hand, flow velocity
decreases when it is passing on the lower (generally concave) surface of airfoil and
as a result, pressure on this surface increases. Moreover, friction between air and
airfoil surface exists and air flow velocity decreases when it reaches to airfoil
surface. These pressure differences and friction create a net force and moment on the
airfoil.
The net force acting on an airfoil is divided into two components as lift force
and drag force. Lift force is the component of the net force on an airfoil
perpendicular to flow direction. Drag force is the component of the net force on an
airfoil parallel to flow direction. Moment which is acting on quarter chord is called
as pitching moment.
Lift = l = Cl . ½ . ρ. U2 . c
Drag = d = Cd . ½ . ρ. U2 . c
Moment = m = Cm . ½ . ρ. U2 . cr
In this equation,
Cl is airfoil lift co efficient,
Cd is airfoil drag co efficient,
Cm is airfoil moment co efficient,
c is the chord length.
Flow passing on the surface of an airfoil is not always the same. Related to
the effects such as velocity, temperature, air ambient pressure, viscosity, the length
of airfoil etc., flow has different characteristics. As a result, forces and moments on
an airfoil are different. Most of these effects are represented by a non dimensional
number which is called as Reynolds Number. Reynolds number is the ratio of the
inertia forces over viscous forces.
15
In this formulation,
U velocity of air,
L reference length,
ρ is fluid density,
µ is dynamic viscosity and
υ is kinematic viscosity.
Reynolds number basically represents character of the flow and it has direct
effects on the force co efficient.
In aircraft applications, Reynolds numbers are usually high, much more than
a few millions. However, in wind turbine applications Reynolds numbers are usually
low (except huge wind turbines), less than a million or only a few millions, since the
wind velocities are very low. This means that airfoils designed for high Reynolds
numbers may not be suitable for low Reynolds number applications. In order to
design a wind turbine, real characteristics of the airfoil has to be known and decision
should be done by considering these effects.
3.5 AIRFOIL DATABASE
In the BEM analysis and optimization performed in this thesis, airfoil force co
efficient information from different airfoils is needed. In the optimization studies,
different airfoils and airfoil families are included into the optimization process. An
airfoil database is set up for this purpose. This airfoil database consists of many
airfoils or airfoil families designed for wind turbines or used in wind turbine
applications. In the database, lift and drag co efficient for a range of angle of attack
values and for different Reynolds numbers are used. The main goal of this criterion
16
is to perform BEM theory analysis more accurately. By keeping 2D section data
accuracy of a wind turbine blade as close to real as possible, wind turbine
performances are predicted as accurate as possible.
There are two groups in the database. First group consists of airfoils belongs
to an airfoil family. There are single airfoils not belong to any airfoil family but still
kept in the data base for single airfoil applications along a wind turbine blade. 11
airfoil families found in the literature are used in the database. These families are
shown in Table 3.1.
Table 3.1 Airfoil families used in airfoil database
Name of Family Number of Airfoils
in the Family
Thickness Range
(percent of chord) Re Number Range
NACA 63-2xx 3 15 to 21 1.0E6 - 9.0E6
NACA 63-4xx 4 15 to 30 1.0E6 – 9.0E6
NACA 64-4xx 2 15 to 21 3.0E6 – 9.0E6
NACA 65-4xx 2 15 to 21 3.0E6 – 9.0E6
Risoe A1 3 18 to 24 1.6E6
FX-61 4 14.7 to 18.4 1.0E6 – 3.0E6
DU 2 21 to 25 1.0E6
FFA-W3 3 21 to 30 1.4E6 – 1.8E6
FX-60 3 12.6 to 17.7 1.0E6 – 3.0E6
FX S 2 15.8 to 19.6 1.0E6 – 3.0E6
FX-66 4 16.1 to 19.6 1.0E6 – 3.0E6
17
3.6 AIRFOIL Cl , Cd DATA INTERPOLATION & EXTRAPOLATION
Figure 3.5 Airfoil data interpolation for angle of attack results compared with
originals.
Airfoil database includes Cl and Cd data of many airfoils for various
Reynolds number data. To apply this airfoil information to the iteration procedure in
BEM analysis code, an interpolation method is chosen. 3D surface. With this
method, airfoil coefficients are stored as surfaces according to changing angle of
attack and Reynolds number. Interpolation examples are shown in Figures 3.5 and
3.6.
Figure 3.6 Airfoil data interpolation for Reynolds number results compared with
originals.
18
In the Figure 3.7 extrapolated airfoil data by using Airfoil Prep v2.2 are
shown and compared with original limited angle of attack values. Before a new
airfoil is added to the airfoil database, its coefficients have to be pre-processed with
Airfoil Prep for high angles of attack values. Then, BEM analysis code is able to
analyze wind turbines in very high and low angles of attack within the limits of this
extrapolation accuracy.
Figure 3.7 Airfoil data interpolation for Reynolds number results compared with
originals.
19
CHAPTER 4
PROBLEM IDENTIFICATION
One of the major challenges in this century is the efficient use of energy
resources as well as the growing production of energy from renewable sources.
There are several alternative forms of energy that have been explored and developed
such as geothermal, solar, wind and hydroelectric power. The affordability and
performance of renewable energy technologies is the key to ensure the availability
to the mass market.
The present wind turbines blades are carried out with sharp trailing edge
which leads to the damage of the blades at the trailing edge end of the blade. This
damage will lead to the reduction of the efficiency of the blade to a certain limit.
The tip damage of the blade is the most common type of damages seen in the
present blades which can be avoided by increasing the thickness of the trailing edge
of the blade.
Furthermore, the turbine "blade thump" noise causes a health problem known
as Wind Turbine Syndrome. Other major problems for the human due to the noise
produced by the wind turbines are sleep disturbance headache, Eardrum damage,
Dizziness, Vertigo, Nausea, Visual blurring, Rapid Heart rate, Concentration
Problems.
By carrying out the project in modifying the airfoil design and introducing the
winglet to blade design the noise of the wind turbine blades can be reduced and
efficiency is improved. The profile of the blade will change post flow of the air that
will reduce the above mentioned problems up to a certain level.
20
CHAPTER 5
OBJECTIVE
1. To increase the reliability of wind turbine blades through the development of the
airfoil structure.
2. To modify the contemporary blade design to the new altered design for the better
performance of the wind turbine.
3. To implement the winglet to the blade design to reduce the wind turbine noise for the
same wind condition and atmospheric situations.
4. To compare the output of both the type of blades by carrying out the Experimental
method of testing under same conditions.
21
CHAPTER 6
DESIGN CONSIDERATIONS
6.1 AIRFOILS AND BLADE GEOMETRY
In order to select a main blade to conduct the most extensive part of the
optimization, 2 random winglet configurations are taken from the design parameters
range table. A blade is selected to perform more extensive optimization experiments
after implementing a winglet. Selecting a single blade avoids having to implement
the winglet in three different blades, reducing the experiment time outrageously.
There are many different types of airfoils used for wind turbine rotor blades.
Some researchers have used blended wings using two different types of
airfoils in order to achieve the desired design. Such a design is shown in Figure 6.1.
Figure 6.1 Blade profiles from NACA 63-430 and NACA 63-215.
As it can be observed, the NACA series airfoils are quite popular in this type
of application. However, it has been shown that these airfoils have noticeable
performance degradation from roughness effects resulting from leading-edge
22
contamination. This leads to energy losses which can be of great importance for
stall-regulated rotors. The National Renewable Energy Laboratory (NREL) began its
development of new airfoils specific for wind turbine application. The annual
energy improvements from the NREL airfoil families are projected to be 23% to
35% for stall-regulated turbines, 8% to 20% for variable-pitch turbines and 8% to
10% for variable-rpm turbines.
6.2 WINGLET DESIGN
The geometry of a winglet is defined by six parameters
Height
Sweep angle
Cant angle
Curvature radius
Toe angle
Twist angle
The geometry of winglets has been extensively investigated for the
aeronautical industry and specifically for high performance sailplanes. Since it has
been shown that winglets decrease drag and improve aerodynamic performance of
wind turbine rotor blades, it is important to understand and analyze the design and
performance improvement process that these researchers used for this application.
This gives a good overview and provides with ideas on how to manage the design
process for the wind turbine application.
23
Figure 6.2 Parameters describing winglet geometry.
These geometric parameters can serve as the variables for input to the
optimization algorithm in order to find the optimal shape given the aerodynamic
constraints and goals.
Figure 6.3 Winglets with different sweep angles
24
Figure 6.4 Winglets with different height
6.3 DESIGN COMPONENTS
In order to completely test any winglet design and notice to prove any
improvements delivered from winglet design alternatives, the design must be tested
on an existing wind turbine configuration for which power output, aerodynamic and
operational data are known or can be found.
The proposed wind turbine to conduct all aerodynamics and structural studies
consists of an upwind tri-blade horizontal axis turbine, with a rotor diameter
D=3.2m, rotor height h= 7.62 m, power output of approximately 2 kW, tip speed
ratio of 4-10, at a wind speed of 0-5 m/s. Based on this design, the blades are
changed and tested, and winglets are implemented and tested.
To attain maximum power generation from a wind turbine, the correct and
optimized design of the blades is necessary. An optimal blade features a maximum
lift coefficient for which roughness has no effect. It is also a goal of the airfoil
family to reach the minimum Cd/Cl possible. Through the length of an optimal
25
blade, different airfoil shapes are present. Usually, 3 to 5 different airfoil shapes are
distributed along a blade, and the distance between them depends on the behavior of
the flow around each individual airfoil at a radial position from the rotor center.
In the extent of this project, three different families of airfoils are tested for
best performance, with and without a winglet. From a specified rotor diameter, wind
speed and range of tip speed ratio, and a random selection of two winglet
configurations, the three blade configurations are tested for maximum Cl . The best
performing blade featuring a winglet is to be used for further winglet design
optimization; however, final optimized designs are to be tested in all three blades.
The airfoil families to be used in this project have been extracted from various
sources, including a paper from the National Renewable Energy Laboratory (NREL)
and Airfoils Inc., and the RISO DTU National Laboratory for Sustainable Energy.
6.4 THEORETICAL DESIGN
6.4.1 BLADE PITCH ANGLE
A critical part of the rotor design includes the selection of either a variable
speed ratio or a fixed speed ratio, and this is determined by either implementing a
variable blade pitch system or selecting a fixed blade pitch angle. For the purpose of
this project, a fixed blade pitch angle is chosen.
Recalling previous definitions, the tip speed ratio is defined as the ratio
between the blade tip speed and the wind speed. Since the wind speed in a regular
environment is a variable phenomenon, it is physically right to say that having a
fixed blade pitch angle produces a variable tip speed ratio. An optimal blade pitch
angle is attained by means of BEM and later optimized through CFD.
26
6.4.2 BLADE TWIST ANGLE
A variable angle of attack through the length of the blade is given by a
specified twist angle. The distribution of the twist angle is based on the aerodynamic
behavior (Cd/Cl and other parameters) of each individual airfoil at a certain angle of
attack. This angle of attack is then translated to the angle of relative wind by adding
the initial twist angle of the blade. Equation yields to the angle of relative wind φ.
Where,
λr is the local speed ratio,
φ is the blade twist angle.
The distribution of the twist angle is given in the proposed design, and it is equal to
φ minus the angle of attack α.
6.4.3 CHORD DISTRIBUTION
The chord length of each airfoil in a blade is also variable, and it is obtained
with Equation
Where,
B is the number of blades .
The distribution of the chord length is given in the proposed design.
6.4.4 PROPOSED INITIAL DESIGN
The design of the blade has been preliminarily performed using Q-blade,
available wind turbine blade design software which works together with X-foil in
order to design and analyze a blade with different airfoils for each cross section as
well as twist angle along the length of the blade.
The parameters for the design of the blade were taken from a student design
optimization in which a wind turbine blade was optimized using several
27
methodologies including design of experiments (DOE), gradient-based sequential
quadratic programming optimization and a multi objective genetic algorithm. The
objective functions of this optimization project are to maximize the power output
while minimizing the blade volume and structural stress. The chosen blade radius is
1.6 m, and in the airfoil used is 63 series especially 63-215, 63-215 (Modified), 63 -
415.
Given that the purpose of this B.E. thesis is the design, analysis and testing of
airfoil and winglets, the blade design will be based upon the findings of this real
time project. In order to have an original blade design for this project, the following
NACA airfoil family was used for the blade geometry. Table 6.1 shows the
configuration for a medium to large blade length recommended by NACA.
Unlike typical airfoils used in aeronautics, these airfoils have been
specifically designed for wind turbines. The camber in these airfoils is higher than
others the thickness of the blade is higher at its root, and decreases along its length,
until the thinnest airfoil is used at the tip.
Table 6.1 Airfoils for blade design
Blade Length
(m)
Generator (kW)
Thickness
Airfoil family (root to tip)
1 – 3 1.5- 5 15-21 Rectangle 63- 215 63-215
(modified)
63-
415
The location of the airfoil family along the length of the blade is described in Table
6.2, where x is the position from the root to the tip of the blade and R is the radius of
the blade (1.6 m).
28
Table 6.2 Position of airfoils along length of the blade
Airfoil x/R x(m)
63 - 215 0.3 0.48
63 – 215 (Modified) 0.4 0.64
63-415 0.75 1.2
The twist angle, defined as the angle between the airfoil chord line and the
plane of the blade rotation, is shown in Table 6.3. Also, another parameter that is
detailed in this table is the chord length of the airfoil. It can be observed that the
chore length decreases along the length of the blade. This design technique is called
tapering.
Table 6.3 Parameters for blade design
X (m) x/R Twist angle (deg)
Chord length (m)
0 0 0 0.192
0.18 0.474 2.5 0.172
0.36 0.643 5.0 0.151
0.54 0.730 7.5 0.131
0.72 0.783 10.0 0.111
0.90 0.818 12.5 0.091
1.08 0.844 15. 0.070
The design is given as a list of X, Y and Z coordinates of the section airfoil
at each x/R. This enables the user to import each cross section as a curve in a CAD
29
program, a spline is used to connect the point cloud and the part can be created by
means of a blend option, such as in Pro Engineer.
Figure 6.5 Sections of blade
Figure 6.6 2D Airfoil in Pro Engineer
30
Figure 6.7 Curves in blade
Figure 6.8 Airfoil twist in blade
31
Figure 6.9 Isometric view of Finalized Normal blade
Figure 6.10 Winglet design
32
Figure 6.11 Winglet geometry in Pro Engineer
Figure 6.12 Winglet blade final design – Isometric view
33
Figure 6.13 Winglet blades with hub
Figure 6.14 Isometric view of hub
34
Figure 6.15 Isometric view of nose
Figure 6.16 Isometric view of nacelle
35
Figure 6.17 Isometric view of tower
Figure 6.18 Assembled view of Present design
36
Figure 6.20 Assembled view of new design (Winglet)
6.5 FINAL DESIGN WITH WINGLET
6.5.1 SIZING AND PARAMETERS
There are several sizing aspects involved in the design of a wind turbine,
specifically a wind turbine blade. Based on previous designs and research, an
optimal blade design has been used in this project, involving airfoils, twisting, setup,
and scaling factors.
The rotor diameter for the wind turbine is 3.0 meters, and the winglet
configuration selected will add approximately 0.2 meter to this dimension,
37
depending on the configuration used. This dimension could be altered by changes in
one or more characteristics of the winglet.
The design parameters of the winglet that this project involves are height, radius and
cant angle.
6.5.2 CANT ANGLE
The cant angle of a winglet has been previously defined in this report. The
range of variation for the cant angle for the purpose of this project is from 10° to
90°.
6.5.3 RADIUS (Percentage of Height)
The radius between the turbine blade and the winglet varies as a function of
the winglet height; therefore the parameter setup for this case is a multiple of the
height. The radius varies from 10% to 100% of the height of the winglet,.
6.5.4 HEIGHT
The height of the winglet fluctuates in relation with the turbine rotor radius,
varying from 1% to 2% of the rotor radius. This parameter is setup to change in the
range of 0.16 to 0.32 meters.
6.6 FINAL CAD DESIGN
The blade final design is based on the NACA airfoil family as the preliminary
design. The length of the blade changed due to prototyping and testing issues. The
new airfoil configuration is shown in Table 6.4, 6.5 and 6.6.
38
Table 6.4 Airfoil Station Distribution for Final Blade Design
X (m) x/R Twist angle (deg)
Chord length (m)
0 0 0 0.192
0.18 0.474 2.5 0.172
0.36 0.643 5.0 0.151
0.54 0.730 7.5 0.131
0.72 0.783 10.0 0.111
0.90 0.818 12.5 0.091
1.08 0.844 15. 0.070
Table 6.5 Airfoil Configuration
Airfoil x/R x/R x(m)
63 - 215 0.3 0.48
63 – 215 (Modified) 0.4 0.64
63-415 0.75 1.2
Table 6.6 Final Winglet Parameters
Height 0.15 meters
Radius 0.05 meters
Cant Angle 60 degrees
39
CHAPTER 7
ANALYSIS
When the mesh was completed, it then could be imported into FLUENT and
after checking for possible errors and overall quality of the mesh, the simulation
setup could be started. The application of a single moving reference frame gives the
advantage of rendering the transient nature of a rotating problem a steady problem,
however it was observed that at high wind speed velocities, when residuals reached
a constant value, a small quasi-sinusoidal trend would develop; this suggests, that
the problem still presents unsteady features, therefore, an appropriate transient input
should be given. The mesh file of the wind turbine blade assembly is shown in the
Figure 7.1.
Figure 7.1 Meshed Wind Turbine Assembly with boundary
40
7.1 BOUNDARY CONDITIONS
The setting of the Boundary Conditions (BCs) is a very important step,
therefore BCs have to be properly applied. Below is a list of the used boundary
conditions:
7.1.1 VELOCITY-INLET
When dealing with incompressible flows, the velocity must be specified at the
inlet of the mesh. It can be specified as both constant and variable, either normal to
the surface or acting with a specified angle (as would be in a yaw-study case). In
this case it was specified as constant and perpendicular to the boundary. Turbulence
conditions also have to be defined here and the default turbulence parameters of the
NASA Ames Wind Tunnel were used, that is, inlet turbulence intensity of 0.5 % and
viscosity ratio set to 10.
Figure 7.2 Inlet and Outlet of the boundary
41
7.1.2 PRESSURE-OUTLET
This boundary condition was applied at the outlet of the domain and sets the
pressure at the boundary at a specific static pressure value. In this study, the obvious
choice was to put the value equal to zero so that the pressure at the outlet would be
equal to the atmospheric operating pressure (standard pressure at sea level was used,
i.e. 101,325 Pa)
Figure 7.3 Imported parts in Hypermesh
Figure 7.4 Meshed part in Hypermesh
42
Figure 7.5 Meshed Nose and Hub
Figure 7.6 Meshed Winglet
43
7.1.3 NO-SLIP WALL
This condition is applied to the solid surface of the blade, and implies the
velocity of the fluid particle to be zero at the wall.
7.1.4 PERIODIC CONDITION
Since the wind turbine rotor rotates at a constant angular velocity thus
presenting a periodically repeating nature; the software allows applying periodic
boundary conditions to specific surfaces giving the great advantage of reducing the
size of the domain.
7.1.5 SYMMETRY
The boundary conditions allow a surface to be treated as a zero-shear wall. A
summary of the assigned boundary conditions is given below.
Table 4.2: Assigned boundary conditions
Parameter Values
Inlet velocity 2.0 – 4.0 m/s
Outlet Outflow
Rotating Part Speed 800 rpm
Operating Pressure 0 Pa
7.2 SOLUTION METHOD
As was introduced in Section 3.4, the pressure-based discretization scheme is
being applied and since computing hardware permitted, the coupled algorithm,
which solves in one step the system of momentum and pressure-based continuity
equation, could also be used, thus reducing computational times.
With FVM, scalar quantities are defined at the centre of cells whereas
convection terms are stored at the face of the cells. These last terms can only be
found by means of interpolation from the centre of the control volume, namely
44
upwind scheme. In the software, there are different methods that can be used such as
first- or second-order upwind scheme.
According to the FLUENT Theory Guide, the latter is in most cases
preferable as error margins are decreased. However, as recommended by FLUENT,
the solution should initialized with first-order upwind scheme and when some
convergence is achieved, it can be switched to second order. This is done in order to
limit divergence problems.
Figure 7.7 Iterations for Wind speed 2.0 m/s
45
Figure 7.8 Static Pressure for Wind speed 2.0 m/s
Figure 7.9 Velocity Magnitude for Wind speed 2.0 m/s
46
Figure 7.10 Iterations for Wind speed 3.0 m/s
Figure 7.11 Static Pressure for Wind speed 3.0 m/s
47
Figure 7.12 Velocity Magnitude for Wind speed 3.0 m/s
Figure 7.13 Iterations for Wind speed 4.0 m/s
48
Figure 7.14 Static Pressure for Wind speed 4.0 m/s
Figure 7.15 Velocity Magnitude for Wind speed 4.0 m/s
49
CHAPTER 8
MANUFACTURING OF BLADE
8.1 OVERVIEW OF PRODUCTION PROCESS
The production process is as follows:
1. Produce an original blade from which to make copies. This would usually be
carved from wood.
2. A fiber-glass female mould is then taken from the original. This mould is in two
halves. This mould can be used a number of times.
3. The two halves of the blade are then made separately using a number of layers of
glass fiber mat and resin.
4. When dry, these blade halves are then carefully cut and the edges tapered to that
the two halves fit carefully together.
5. A wooden insert is fitted into the root of the blade. This provides material for
which to screw into and provides some compressive strength.
6. A fiber-glass ‘stringer’ is fixed into one blade half. This is carefully cut down so
that the other blade half fits exactly on top. This ‘stringer’ gives strength to the blade
from root to tip.
7. Additional pieces of fiber glass mat are stuck to the ‘stringer’ using resin. This
gives a large area onto which the other blade half can be stuck.
8. The other blade half is stuck onto the first. This is then fitted back into the mould
and clamped together to ensure it dries in the correct shape.
9. A two-part expanding foam is then used to fill the blades.
10. Any imperfections in the blade are then filled with good quality filler which is
then sanded back. A thin veil is added to the leading edge to join the two halves and
for protection (this edge will be worn away in time due to the wind). The blade is
then sanded to a smooth finish.
11. Depending upon the surface quality and desired finish, the blades may need to
be painted.
50
8.2 BASIC DESIGN
The blade is comprised of two main halves (both made from fiber glass), a
wooden core at the root and a ‘stringer’ along the inside from root to tip. Once the
blade has been constructed and stuck together, a two-part expanding foam is used to
fill the structure of the blade helping to add strength and rigidity to the blades.
Figure 8.1 Two equal halves of blade
8.3 EQUIPMENT REQUIRED
The blades are made from what is commonly referred to as fiber glass. This is
mixture of glass fiber (maybe this is obvious, eh?), which has great strength in
tension and compression, resin, which provides rigidity when set, and a number of
other chemicals. The various chemicals required are listed here along with their use
and any special precautions required.
The various tools required are also listed here. Ensure that you have all this
equipment before starting the manufacturing process. Fiber glass product suppliers
will typically stock all the materials and chemicals required.
51
8.4 MATERIALS AND CHEMICALS REQUIRED
8.4.1 RESIN
There are many different types of resin, each with different properties. To
keep the design relatively simple, only two types of resin have been used for the
blade manufacture:
8.4.2 RESIN TYPE ‘R 10-03’
Figure 8.2 Resin Type ‘R 10-03’
This is a general purpose rigid orthopthalic (FRP) polyester resin. (Type ‘R
10- 03’ is a local manufacturer’s code number). It is relatively inexpensive and is
used for the majority of the wind turbine blades.
8.4.3 RESIN TYPE ‘POLYMER 31-441’
Figure 8.3 Resin Type ‘Polymer 31-441’
This is called a ‘gel coat’ polyester resin. (Again, type ‘Polymer 31-441’ is a
local manufacturer’s code number) It is 100% isophthalic with Neo-Pentyl Glycol
(NPG). It is very hard wearing and is scratch and chemical resistant. It is more
52
expensive than the other type of resin therefore its use is limited to just the outer
layers of the blade.
8.4.4 STYRENE MONOMER
This is mixed with the resin to reduce the viscosity of the resin. This makes
the resulting mixture more workable and easier to ‘paint’ onto the fiber glass cloth.
8.4.5 HARDENER
Figure 8.4 Hardener
Hardener is added to the resin mix to start the solidification (or curing)
process. The time taken before the resin sets is controlled by the amount of hardener
and accelerator (cobalt) added. Once the hardener is added to the resin it must be
worked quickly into the fiberglass as the resin will solidify quickly. An imported
MEKP hardener is used due to its more reliable properties and hence more reliable
resin setting time.
8.4.6 DURA WAX
Figure 8.5 Durawax
53
This is a release agent. It is applied to the mould before each ‘lay-up’ to
ensure that the item produced does not stick to the mould. Sometimes a thin non-
stick film is added to moulds to avoid the part sticking – given the complex curved
shape of the moulds a wax release agent was selected.
8.4.7 CHOPPED STRAND FIBER GLASS MAT (CSM)
The fibers within CSM are in random orientation. This means that it has the
same strength in every direction. It is the cheapest and easy to work with, as its
orientation does not matter. It is available in different weights. 300gsm (grams per
square meter) is used to produce the moulds and a thin ‘veil’ of 100gsm is used to
join the sides and protect the leading edge.
8.4.8 WOVEN CLOTH FIBER GLASS (WC)
Figure 8.6 Woven Cloth Fibre Glass
This consists of woven strands. It is very strong in the direction of the weave
but is slightly more expensive and harder to work with as the orientation of the
weave when the piece is cut must be carefully chosen. The cut weave has a tendency
to unravel when it is handled in a dry state. Only 200gsm is used here.
8.4.9 THINNERS
Lacquer thinners are required to remove excess resin and to clean up any
spills, paint brushes, pots and tools. It is extremely flammable.
54
8.4.10 WOODEN CORE ROOTS
Figure 8.7 Wooden core roots
A small amount of marine-grade plywood is required to form a wooden core
for the root of the blade. This was built up from a number of layers of plywood until
the correct thickness was obtained.
8.5 TOOLS REQUIRED
Safety equipment:
Goggles
Respirator / masks
Ensure good quality item as the process generates large amounts of very fine
toxic dust.
Figure 8.8 Safety Equipments
Gloves
Syringes (or pipettes)
55
Pots and mixing sticks
Scales
Paint brushes
Scissors
Marker pens
Rags/cloths
Sandpaper
Power grinder with cutting disk and sanding disk
Mixing tools and spatulas for car body filler
8.6 HALF BLADE MANUFACTURE
As shown in the basic design, the blade is comprised of two blade halves, the
windward half and the backward half. This section explains the process of
producing the two blade halves (the next sections explain the process of joining the
two halves and finishing the blade). Each blade half is built up from 16 layers of
fiber glass mat. Woven cloth (WC) is used for additional strength in the direction
the forces act on the blades.
This process requires careful preparation beforehand to ensure that the
process of building the blade goes smoothly and quickly. If the resin is allowed to
set while the blade halves are being manufactured then this could result in a weaker
blade due to de-lamination between the two dry layers.
The general process is as follows:
1. Preparation: Cut the layers of fiberglass WC. 16 layers are used in each half.
2. Preparation: Prepare batches of resin mixture and the corresponding batches of
hardener.
3. Preparation: Wax the mould to ensure easy release.
56
4. Procedure: Fill the moulds with a layer of resin, then a layer of fiberglass WC
until all 16 layers have been placed. The weave of the WC must be rotated by 45
degrees between each layer.
5. Procedure: Leave to dry.
8.7 BLADE JOINING
When set, the two halves of the blade need to be joined to form a single unit.
To do this they need to be accurately cut so that the two pieces fit together. The join
should be made with minimal impact on the blades aerodynamic shape. The final
piece should appear as close to the original wooden mould as possible. Also
additional strength and rigidity is added to the blade through the use of a ‘stringer’
from the root to the tip. A wooden core is inserted at the root. This is so the screws
used to hold the blades to the wind turbine have something to ‘bite’ into. It also
stops the blade root collapsing when the front blade assembly is bolted onto the
generator on the wind turbine.
8.8 BLADE FINISHING
Now that the blade halves have been stuck together and filled with foam, the
last stage is the blade finishing. This involves filling any gaps on the blade edges,
adding a thin ‘veil’ of fiber glass to the leading edge, sanding down any
imperfections and painting (if required). Fill any gaps along the leading edge with
good quality filler, such as car body filler. Leave this to dry. Sand the blade along
the leading edge and ensure that the surface is smooth. Add a narrow strip of CSM
fiberglass to the leading edge. Lightweight 100gsm CSM was used for this, although
200gsm CSM may also work. Additional resin will be required and, as this will be
exposed to the sun, this should be outer layer resin mixture. Approximately 200g of
resin will be required. Once dry, sand again.
Fill any gaps on the blade surface with good quality filler, such as car body
filler. Leave this to dry. Sand the blade to ensure that all the surfaces are smooth,
57
especially along the leading edge. The edge of the trailing edge should be thin,
approximately 1mm or less width. This will be the final sanding process. Clean the
blade well to remove any dust or dirt. If toner has not been used, the blades will
need painting, both for protection and aesthetics. Good quality paint should be used,
preferably with an undercoat layer. Spraying is the preferred (and easiest) method of
application. The next stage is to drill the holes to attach it to your wind turbine
generator.
58
CHAPTER 9
TESTING & VALIDATION
9.1 TESTING CONDITIONS
The testing condition was up to the standard atmospheric state in the field. The
various parameters noted during the test are listed below:
Table 9.1 Testing Conditions
Description Values
Temperature 26 – 29 oC
Wind speed 1.8 – 4.6 m/s
Pressure 101.325 N/m2
Tower Height 7.12 m
Generator Capacity 2 KW
Output mode 3 Phase
Plane Blade weight 2.899 kg
Winglet blade weight 3.112 kg
Test dates
For plane blade 14.03.2013 – 16.03.2013
For winglet blade 18.03.2013 – 20.03.2013
The conditions were checked in the field for a particular interval of time
period. The wind speed was checked with the anemometer and then the output values
are taken from the testing of the wind turbine setup. The blade assembly is lifted to
that height with the help of cranes and assembled with the help of man power.
59
9.2 PLANE BLADE TESTING
The Plane blades are assembled t the tower of the wind turbine for the analysis
in a realistic manner. First the plane blade is assembled to the tower with the
generator. The specifications of the tower and other components are discussed
previously. The various values like voltage and current for various speed is
measured using the multi meter in the form of three phase formats. The test is carried
in a standard atmospheric condition. The obtained values for the plane blade are
tabulated as below:
Table 9.2 Voltage and Current value for Plane blade
WIND SPEED
VOLTAGE AMPS R Y B R Y B
2.00 49 48 49 1.08 1.06 1.08 2.10 48 47 48 1.06 1.03 1.06 2.20 59 57 55 1.30 1.25 1.21 2.30 60 63 66 1.32 1.39 1.45 2.40 69 68 65 1.52 1.50 1.43 2.50 70 69 69 1.54 1.52 1.52 2.60 69 68 65 1.52 1.50 1.43 2.70 70 74 79 1.54 1.63 1.74 2.80 66 64 64 1.45 1.41 1.41 2.90 78 79 77 1.72 1.74 1.69 3.00 61 61 63 1.34 1.34 1.39 3.10 75 73 73 1.65 1.61 1.61 3.20 73 73 72 1.61 1.61 1.58 3.30 79 78 78 1.74 1.72 1.72 3.40 71 70 68 1.56 1.54 1.50 3.50 70 81 80 1.54 1.78 1.76 3.60 82 85 85 1.80 1.87 1.87 3.70 89 89 88 1.96 1.96 1.94 3.80 89 88 87 1.96 1.94 1.91 3.90 90 92 91 1.98 2.02 2.00 4.00 99 97 99 2.18 2.13 2.18
60
9.3 WINGLET BLADE TESTING
Then the plane blades are replaced with the blade with the winglet for the
testing in the same condition and manner. . The specifications of the tower and other
components are discussed previously. The various values like voltage and current
for various speeds is measured using the multi meter in the form of three phase
formats. The blade is carried out for the test run for a time period of 3 consecutive
days. The obtained values of current and voltage at various speeds are listed as
below:
Table 9.3 Voltage and Current value for Winglet blade
WIND SPEED
VOLTAGE AMPS R Y B R Y B
2.00 51 49 53 1.12 1.08 1.17 2.10 53 54 55 1.17 1.19 1.21 2.20 50 49 47 1.10 1.08 1.03 2.30 55 57 59 1.21 1.25 1.30 2.40 62 59 64 1.36 1.30 1.41 2.50 69 74 72 1.52 1.63 1.58 2.60 75 77 79 1.65 1.69 1.74 2.70 88 87 90 1.94 1.91 1.98 2.80 91 85 76 2.00 1.87 1.67 2.90 89 90 91 1.96 1.98 2.00 3.00 92 94 90 2.02 2.07 1.98 3.10 80 71 64 1.76 1.56 1.41 3.20 93 84 90 2.05 1.85 1.98 3.30 95 94 96 2.09 2.07 2.11 3.40 100 101 99 2.20 2.22 2.18 3.50 103 102 101 2.27 2.24 2.22 3.60 105 100 104 2.31 2.20 2.29 3.70 109 108 107 2.40 2.38 2.35 3.80 112 105 107 2.46 2.31 2.35 3.90 120 118 116 2.64 2.60 2.55 4.00 124 122 120 2.73 2.68 2.64
61
Figure 9.1 Efficiency Calculations for Winglet Blade
9.4 VALIDATION
9.4.1 VOLTAGE vs. WIND SPEED
Figure 9.2 Wind speed vs. Voltage (3 phase) – Plane blade
2.0 2.5 3.0 3.5 4.040
50
60
70
80
90
100VOLTAGE VS WIND SPEED(PLANE BLADE)
WIND SPEED(m/s)
VOLT
AGE(
V)
R Y B
62
Figure 9.3 Wind speed vs. Voltage (3 phase) – Winglet blade
From the above two graphs we compared the output voltage levels of both the
blade in the operating conditions. In the plane blade the maximum output voltage of
99 volts is attained in wind speed 4.0 m/s in R and B phase. In the winglet blade the
maximum output voltage of 124 volts is attained in wind speed 4.0 m/s in R phase.
9.4.2 CURRENT vs. WIND SPEED
From the below two graphs we compared the output current levels of both the
blade in the operating conditions. In the plane blade the maximum output current of
2.18 amps is attained in wind speed 4.0 m/s in R and B phase. In the winglet blade
the maximum output voltage of 2.73 amps is attained in wind speed 4.0 m/s in R
phase.
2.0 2.5 3.0 3.5 4.040
50
60
70
80
90
100
110
120
130VOLTAGE VS WIND SPEED(WINGLET BLADE)
WIND SPEED(m/s)
VO
LTAG
E(V)
R Y B
63
Figure 9.4 Wind speed vs. Ampere (3 phase) – Plane blade
Figure 9.5 Wind speed vs. Ampere (3 phase) – Winglet blade
2.0 2.5 3.0 3.5 4.0
1.0
1.2
1.4
1.6
1.8
2.0
2.2
WIND SPEED(m/s)
AMPS VS WIND SPEED(PLANE BLADE)
AMP
S(A)
R Y B
2.0 2.5 3.0 3.5 4.0
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0 AMPS VS WIND SPEED(WINGLET BLADE)
AMPS
(A)
WIND SPEED(m/s)
R Y B
64
9.4.3 NOISE LEVEL
The noise limits apply to the total noise from all wind turbines and are set for
both weak winds, when noise is found to be most annoying, and stronger winds.
When the noise meets the noise limits it do not mean that the noise is inaudible.
Figure 9.6 Waveform for noise in Plane Blade
Figure 9.7 Noise level graphs for Plane Blade
The noise level produced in the plane blade is illustrated in the above figures.
The noise level was noted at a distance of 3 meters from the tower and that recorded
and analyzed using the Audiopad software. The resulted noise level for the plane
blade is about 109 db.
65
Figure 9.8 Waveform for noise in Winglet Blade
Figure 9.9 Noise level graphs for Winglet Blade
The noise level produced in the winglet blade is illustrated in the above
figures. The noise level was noted at a distance of 3 meters from the tower and that
recorded and analyzed using the Audiopad software. The resulted noise level for the
plane blade is about 78 db.
From this data we are about say that noise level is reduced up to 25% of the
previous values by the implementation of the winglets. The major problems for the
human due to the noise produced by the wind turbines are sleep disturbance can be
certainly reduced by this implementation of modified airfoil and winglet.
66
CHAPTER 10
CONCLUSION
The winglet design process must come after an implementation of final airfoil
design that will be used to compare the improvement of a system with winglets over
one without them.
The blade design of a wind turbine differs from an airplane wing design.
Airplane wings usually have one airfoil design through all the length of the wing, in
the case of wind turbines, around three or four different airfoil profiles are used in
the same blade varying from the root to the tip of the wind. Also, another important
difference can be found in the twist angle of a wind turbine blade. The blade is
twisted in a special and optimized manner through the length of the blade, this do
not happens on an airplane wing.
These differences make the analysis of a wind turbine blade more
complicated than usual. Software and techniques used in airplane design must be
altered in accordance to the needs. For this study, several software packages were
used independently to create and obtain an optimal blade design. The specific
packages used include XFOIL, QBLADE, PRO E W5.0, HYPERWORKS V10.0
and FLUENT 6.3.
The blade design process was very time consuming, methods and techniques
are being refined in order to produce fastest and more reliable designs. The
implementation of the mentioned software packages reduces largely the load of the
design process, and several other packages are in way to be implemented to improve
the blade design and the calculations as much as possible.
67
It has been shown that winglets can effectively improve the performance of a
conventional tip wind turbine blade. The noise level in the wind turbine is also
certainly reduced after the implementation of the winglet the CFD analysis also
shows the better result over the present blade structure.
68
PHOTOGRAPHS
69
70
APPENDICES
APPENDIX 1
NACA 63 - 215 AIRFOIL CO ORDINATES
UPPER SPLINE
0.000000 0.000000 0.003990 0.012500 0.006370 0.015280 0.011200 0.019800 0.023480 0.027920 0.048290 0.039600 0.073230 0.048470 0.098230 0.055690 0.148340 0.066820 0.198520 0.074870 0.248750 0.080490 0.299000 0.083920 0.349260 0.085300 0.399520 0.084570 0.449770 0.081940 0.500000 0.077680 0.550190 0.072030 0.600350 0.065240 0.650470 0.057510 0.700530 0.049060 0.750550 0.040140 0.800510 0.031050 0.850430 0.022130 0.900300 0.013680 0.950140 0.006160 1.000000 0.000000
LOWER SPLINE
0.000000 0.000000 0.006010 -0.011500 0.008630 -0.013880 0.013800 -0.017660 0.026520 -0.024200 0.051710 -0.033280 0.076770 -0.039990 0.101770 -0.045350 0.151660 -0.053360 0.201480 -0.058950 0.251250 -0.062590 0.301000 -0.064480 0.350740 -0.064700 0.400480 -0.063150 0.450230 -0.060040 0.500000 -0.055620 0.549810 -0.050130 0.599650 -0.043820 0.649530 -0.036910 0.699470 -0.029620 0.749450 -0.022240 0.799490 -0.015130 0.849570 -0.008670 0.899700 -0.003340 0.949860 0.000160 1.000000 0.000000
71
APPENDIX 2
NACA 63 - 215 MODIFIED AIRFOIL CO ORDINATES
UPPER SPLINE
0.0 0.0 0.0002 0.0034 0.0004 0.0051 0.0006 0.0064 0.0008 0.0075 0.0010 0.0085 0.0020 0.0125 0.0030 0.0156 0.0040 0.0182 0.0050 0.0205 0.0100 0.0293 0.0200 0.0408 0.0300 0.0489 0.0400 0.0550 0.0500 0.0599 0.0600 0.0640 0.0700 0.0673 0.0800 0.0702 0.0900 0.0727 0.1000 0.0748 0.1250 0.0788 0.1500 0.0816 0.1750 0.0835 0.2000 0.0847 0.2250 0.0855 0.2500 0.0859 0.2750 0.0860 0.3000 0.0859 0.3250 0.0856 0.3500 0.0853 0.3750 0.0852 0.4000 0.0845 0.4250 0.0835 0.4500 0.0819 0.4750 0.0800 0.5000 0.0777 0.5250 0.0750 0.5500 0.0720 0.5750 0.0688
LOWER SPLINE
0.0 0.0 0.0002 -.0011 0.0004 -.0022 0.0006 -.0031 0.0008 -.0037 0.0010 -.0042 0.0020 -.0063 0.0030 -.0079 0.0040 -.0093 0.0050 -.0104 0.0100 -.0150 0.0200 -.0211 0.0300 -.0256 0.0400 -.0294 0.0500 -.0328 0.0600 -.0357 0.0700 -.0384 0.0800 -.0408 0.0900 -.0430 0.1000 -.0450 0.1250 -.0494 0.1500 -.0531 0.1750 -.0562 0.2000 -.0588 0.2250 -.0609 0.2500 -.0625 0.2750 -.0637 0.3000 -.0645 0.3250 -.0648 0.3500 -.0647 0.3750 -.0641 0.4000 -.0632 0.4250 -.0618 0.4500 -.0601 0.4750 -.0580 0.5000 -.0556 0.5250 -.0530 0.5500 -.0501 0.5750 -.0470
72
0.6000 0.0653 0.6250 0.0615 0.6500 0.0576 0.6750 0.0534 0.7000 0.0491 0.7250 0.0447 0.7500 0.0402 0.7750 0.0357 0.8000 0.0311 0.8250 0.0266 0.8500 0.0222 0.8750 0.0179 0.9000 0.0137 0.9250 0.0098 0.9500 0.0062 0.9600 0.0048 0.9700 0.0036 0.9800 0.0023 0.9900 0.0012 0.9950 0.0006 1.0000 0.0000
0.6000 -.0438 0.6250 -.0404 0.6500 -.0368 0.6750 -.0332 0.7000 -.0295 0.7250 -.0258 0.7500 -.0221 0.7750 -.0185 0.8000 -.0150 0.8250 -.0117 0.8500 -.0086 0.8750 -.0058 0.9000 -.0033 0.9250 -.0013 0.9500 0.0001 0.9600 0.0005 0.9700 0.0007 0.9800 0.0008 0.9900 0.0006 0.9950 0.0003 1.0000 0.0000
73
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