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EXPERIMENTAL STUDY OF WIND TURBINE ROTOR
BLADES WITH WINGLETS
A PROJECT REPORT
Submitted by
RAMAKRISHNA DHARMENTHIRA S (42006101034)
SUKUMAR D (42006101041)
YOGESWARAN S (42006101050)
in partial fulfillment for the award of the degree
of
BACHELOR OF ENGINEERING
in
AERONAUTICAL ENGINEERING
TAGORE ENGINEERING COLLEGE, VANDALOOR (POST)
ANNA UNIVERSITY:: CHENNAI 600 025
MAY 2010
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BONAFIDE CERTIFICATE
Certified that this project reportEXPERIMENTAL STUDY OF WIND TURBINE
ROTOR BLADES WITH WINGLET is the bonafide work of
RAMAKRISHNA DHARMENTHIRA S (42006101034), SUKUMAR D
(42006101041) AND YOGESWARAN S (42006101050) who carried out the
project work under my supervision.
SIGNATURE SIGNATURE
Dr. P. Baskaran Mr. P. Saravanan
PROFESSOR AND HEAD OF DEPARTMENT SUPERVISOR AND LECTURERDepartment of Aeronautical Engineering Department of Aeronautical Engineering
Tagore Engineering College Tagore Engineering CollegeRathinamangalam Rathinamangalam
Chennai600048 Chennai600048
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ACKNOWLEDGEMENT
We would like to express our sincere thanks and gratitude to Dr. P.Baskaran,
Prof and Head of the Department, Aeronautical engineering for offering all the
support and encouragement that was instrumental in the successful completion of the
project.
We also thank Mr.P.Saravanan, M.E., Our Supervisor for having given us
valuable suggestions and support to make this project successful.
We would also like to thank all our department staffs for providing the
necessary facilities and helping us in every point during the completion of our project.
We acknowledge the support given by all the faculty members, lab technicians,
friends and family members for the completion of the project.
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TABLE OF CONTENTS
CHAPTER NO. TITLE PAGE
ABSTRACT iii
LIST OF TABLES v
LIST OF FIGURES vi
NOMENCLATURE vii
1. INTRODUCTION
1.1 Wind turbine 1
1.2 Importance of rotor 2
1.3 Winglets 3
1.4 Composite materials 6
1.5 Objective 6
1.6 Methodology 7
1.7 Importance of work 7
2. EXPERIMENTAL PROCEDURE
2.1 Model selection 8
2.2 Model fabrication 12
2.2.1 Wind turbine tower 12
2.2.2 Wind turbine rotor 14
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2.3 Experiment instruments 17
2.4 Experimental methodology for models efficiency study 21
2.5 Experimental methodology for noise comparison 31
2.6 Experimental methodology for rotor wake study 35
3. RESULTS AND DISCUSSION
3.1 Result 39
4. CONCLUSION 39
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ABSTRACT
For thousands of years mankind is utilizing wind energy. Increasing
world population and increasingly reducing the oil reserves and resulting
requirement for clean, reliable, renewable energy system intensifies the
requirements of wind energy in long term. Nowadays wind turbines are mostly
used for transforming that energy into electrical energy. In order to gain from a
wind turbine economically the efficient wind turbine rotor must be designed
and studied experimentally.
This paper is about experimentally studying the change of efficiency and
performance of wind turbine rotor blades by introducing winglets. The flow
distribution behind the rotor was studied. The wake study helps in planning the
location of the wind turbine in wind farms allowing for the effective utilization
of the available area. During the introduction of winglets in the rotor blades, the
vortices is reduced which in turn reduce the vibration and increase the
efficiency. The reduction of vortices decreases the vibration noise allowing the
wind turbine to work even in populated regions in a reliable manner.
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LIST OF TABLES
Table 1: Technical specifications of Nordtank NTL 550
Table 2: Specification of MN-00
Table 3: Specifications of Winglets
Table 4: Specification of Wind turbine Rotors
Table 5: Wind tunnel specifications
Table 6: RMN-01 power coefficient calculation
Table 7: RMN-02 power coefficient calculation
Table 8: RMN-03 power coefficient calculation
Table 9: RMN-04 power coefficient calculation
Table 10: RMN-00 power coefficient calculation
Table 11: velocity distribution at 1D distance behind rotor
Table 12: velocity distribution at 1.5D distance behind rotor
Table 13: velocity distribution at 2D distance behind rotor
Table 14: velocity distribution at 2.5D distance behind rotor
Table 15: velocity distribution at 2.75D distance behind rotor
Table 16: comparison of Cp and rpm of RMD-00, 01,02,03,04
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LIST OF FIGURES
Figure 1: Typical wind turbine
Figure 2: Schematic diagram wind turbine rotor
Figure 3: Definition of key parameters describing the winglet
Figure 4: Welded projection and sensor in tower
Figure 5: Completely fabricated tower
Figure 6: Wooden pattern of turbine blade
Figure 7: Wax dye
Figure 8: Winglets in rotor
Figure 9: Wind turbine rotor
Figure 10: Image of subsonic wind tunnel
Figure 11: Tip speed ratio vs Cpshmitz
Figure 12: Wind speed vs Slide number
Figure 13: RMD-01 CP vs rpm
Figure 14: RMD-02 CP vs rpm
Figure 15: RMD-03 CP vs rpm
Figure 16: RMD-04 CP vs rpm
Figure 17: RMD-00 CP vs rpm
Figure 18: Noise level in 32bit vs time a) test section b) RMD-03 c) RMD-00
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Figure 19: Velocity distribution at 1D distance behind rotor
Figure 20: Velocity distribution at 1.5D distance behind rotor
Figure 21: Velocity distribution at 2D distance behind rotor
Figure 22: Velocity distribution at 2.5D distance behind rotor
Figure 23: Velocity distribution at 2.75D distance behind rotor
Figure 24: Cp comparison of RMD-00, 01, 02, 03 and 04
Figure 25: rpm comparison of RMD-00, 01, 02, 03 and 04
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NOMENCLATURE
V Wind speed (m/s)
Vc tip speed (m/s)
tip speed ratio
slide number
B Blade number
Cp coefficient of power
CpSchmitz Schmitz number
A Area of the rotor (m2)
p density of air (Kg/m3)
n rotation per minute
r radius of the rotor (m)
D diameter of the rotor (m)
profile profile loss (%)
uc tip loss (%)
Ck lift coefficient
Cd drag coefficient
Pmax maximum theoretical power (watt)
Re Reynolds number
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1.INTRODUCTION
Wind one of the most renewable resources available in our Earth. The
fossil fuels are being slowly degrading due to over-exploitation. This leading us to
start depend more on the renewable resources like wind energy, solar energy and
etc. Wind energy is one most available resource were we can convert them into
electrical energy which can likely satisfy our upgrading needs. This conversion is
done with an ever known machine called as the WIND TURBINE.
1.1Wind TurbineA wind turbine converts the energy of wind into kinetic energy. If the
mechanical energy is used directly by machinery, such as pumping water, cutting
lumber or grinding stones, the machine is called a windmill. If the mechanical
energy is instead converted to electricity, the machine is called wind turbine. A
typical wind turbine is shown in figure 1.
Fig 1. Typical wind turbine
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Wind turbines have the main rotor shaft and electrical generator at the top of a
tower, and must be pointed towards the wind. Small turbines are pointed by a
simple wind vane, while large turbines generally use a wind sensor coupled with a
servo motor. Most have a gearbox, which turns the slow rotation of the blades into
a quicker rotation that is more suitable to drive an electrical generator.
Turbines[Wikipedia]
used in wind farms for commercial production of electric power
are usually three-bladed and pointed into the wind by computer-controlled motors.
A gear box is commonly used to step up the speed of the generator, although
designs may also use direct drive of an annular generator. Some models operate at
constant speed, but more energy can be collected by variable-speed turbines which
use a solid-state power converter to interface to the transmission system
1.2 Importance of RotorRotor
is the device that transforms the available kinetic energy of
wind into mechanic energy. For this reason it is very important for wind turbines.
It is important for blade and blade profiles for to have optimum features, because
these have a direct effect on the efficiency of wind turbine. The rotor commonly
consists of three blades, which are aerodynamically designed airfoils. These airfoil
blades produce lift and drag due to air flows from leading edge. This lift together
with drag force generates the thrust force and the difference of them gives the
driving force which is required to rotate the rotor in an efficient manner. The
blades are designed at certain blade angle in order to face the apparent wind.
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)
Fig 2. Schematic diagrams of wind turbine rotor
1.3 WingletsWinglets are usually intended to improve the efficiency of fixed wing aircrafts.
There are several types and the main purpose is to reduce the drag at the wingtips.
It effectively increases the aspect ratio without increasing the span. The winglets
increase the lift near the wingtip by smoothing the airflow across the upper surface
of blade near the tip and reduce the lift induced drag caused by wingtip vortices.
Adding a winglet to an existing wind turbine rotor will increase power produced
and there is also an additional increase in thrust. The art is then to design a winglet,
which optimizes drag reduction, maximizes power production and minimizes
thrust increase.
The main purpose of adding a winglet to a wind turbine rotor is to decrease the
total drag from the blades which could decrease the vibration and noises due to
them and thereby increase the aerodynamic efficiency of the turbine. Reduction of
total drag is obtained if the additional drag from the winglet is less than the
reduction of the induced drag on the remaining blade.
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During operation of wind turbine blade the resulting pressure difference on the
blades causes inward span wise flow on the suction side and outward span wise
flow on the pressure side near the tip. At the trailing edge, vortices are generated,
which is the origin of induced drag. The resulting pressure difference on an
operating wind turbine blade causes inward span wise flow on the suction side and
outward span wise flow on the pressure side near the tip. At the trailing edge,
vorticity is generated, which is the origin of induced drag.
A winglet is a load carrying device that reduces the span wise flow, diffuses and
moves the tip vortex away from the rotor plane reducing the downwash and
thereby the induced drag on the blade
The key parameters describing the winglets are:
1. Radius of curvature.2. Height3. Cant angle4. Sweep5. Toe6. Twist
Fig 3. Definition of key parameters describing the winglet.
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In this experiment the winglet parameter like height, radius of curvature, cant
angle were considered for designing our winglets. Since based on previous study
[1.pdf]the variation of the other parameters like sweep and twist dint effectively
change the efficiency of the wind turbine rotor. Due the vortices produced at the
wingtips creates large decimals of noise when the wind turbine reaches higher rpm
which would allows to settle the wind turbine away from populated region were
higher power is required. The introduction of winglets can reduce the wingtip
vortices and therefore decreasing the vibrations. This reduction of vibration could
reduce the noise and allow the wind turbine to reach higher rpm increasing its
efficiency.
1.4 Composite MaterialThe result of developing a material to have properties like high strength and
stiffness without gaining weight is the composite material. These composites
overcome the conventional materials like metals and alloy by providing low weight
and cost. Rapid advancement in this material technology[wtbp.pdf]
has created some
variations in the structure of wind turbines. That variation primarily provided
positive impact for lowering the prices of wind turbines and increasing the
strength.
Due to many factors such as mechanical equipment, fatigue, resistance,
corrosion resistance, breaking toughness, rigidity, weight and appearance have
impacts on wind turbine materials. That fact has caused composite materials to be
used widely in wind turbine structure.
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1.5 ObjectiveIn the present work, an attempt is made on comparing the efficiency
of scaled down and redesigned wind turbine rotor blades by introducing four sets
of various winglets to the same wind turbine rotor blades without winglets. A
study in rotor wake of the most efficient wind turbine rotor blades with winglets
was also conducted.
1.6 Methodology
An operational Wind Turbine (Nordtank NTK 550) in scaled down to
the ratio of 1:120. Four winglets of various dimensions which were designed from
the reference of previous studies of winglets were attached to the wind turbine
rotor blades. The total five sets of rotor blade were fabricated four rotors with
winglet and one without winglet. These models were been tested in wind tunnel at
various wind speed and there respective rpm was recorded. Wind turbine rotor with
winglets showed higher rpm and power coefficient than the rotor without wingletallowing possible increase in overall efficiency. The efficient wind turbine rotors
flow distribution after the rotor (rotor wake) is studied by reading the pressure
variation in the area behind the rotor.
1.7 Importance of work
In the development of renewable energy generation the wind turbine plays a
major role. Increase of efficiency with reduction of vibration and noise by using of
winglet increases the reliability and dependence of wind turbine. The design of
wind turbine blades with winglets can be done which could help in increasing the
efficiency and reduction of noise can allowing the wind turbine to locate in
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populated region were the power is required highly, such that the transmission loss
can be reduced in large scale. The study of the rotor wake allows getting
information of the air flow behind the rotor of wind turbine. This information
could help in construction and planning of wind farms, where the air flow of one
wind turbine rotor must not affect the other turbine. This could help in reducing the
area of dependence for required power that gives us high watt per area ratio for
wind farms.
This experimental study could help in designing wind turbine rotor to achieve
higher efficiency by introducing winglets.
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2. EXPERIMENTAL PROCEDURE2.1 Model selection
A wind turbine design was initially required, which allowed us to survey the
commercial wind turbine being operated. This allowed us to come across a
Nordtank wind turbine systems. The Nordtank NTK 550 was selected as our
primary design. Technical specifications of the models are detailed in table 1.
Table 1. Technical specifications of Nordtank NTL 550
Company & Country
originated
Nordtank (U.K)
Model name NORDTANK NTK 550Rated power 550 kilo-watt
Rotor Diameter 41m
Number of blades 3
Swept area 1320.25m
Blade settling angle 20
Length of blade 19.04m
Hub height 35m
Maximum chord 1.65m
Rotational direction Clockwise
Optimum wind speed 13.887m/s
Cut-in wind speed 4m/s
Cut-off wind speed 25m/s
Rotational speed 27.1rpm
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We scaled down the Nordtank NTK 550 wind turbine to a ratio of 1:120. The
respective ratio was selected because of available test section in wind tunnel. This
scaled down model MN-00 was fabricated to specific dimensions in table 2.
Table 2. Specification of MN-00
Rotor Diameter 340mm
Number of blades 3
Swept area 90792.02mm2
Length of blade 141m
Hub height 300m
Maximum chord(root
chord)
32mm
Minimum chord (tip
chord)
13.7mm
Rotational direction Clockwise
Blade settling angle 20
The rotor of MN-00 was taken as basic design for the rotor with winglets. The
winglets were designed from the reference of previous studies. The parameters
considered in designing the winglet was height, can angle and radius of curvature.
Winglet height was taken as 2% and 4% of rotor radius. The cant angle was
selected as 75o
constant since from previous studies this angle was given good
results and radius of curvature were 12.5% and 25% of their respective heights.
The dimensions of these winglets are detailed in table 3.
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Table 3. Specifications of Winglets
Winglet model
nameWMN-01 WMN-02 WMN-03 WMN-04
Height 6.8mm 3.4mm 6.8mm 3.4mm
Cant angle 75o
75o
75o
75o
Root chord 13.7mm 13.7mm 13.7mm 13.7mm
Tip chord 7.46mm 10.58mm 7.46mm 10.58mm
Radius curvature 1.7mm 0.85mm 0.85mm 0.425mm
The total of five sets of wind turbine rotor blades was designed and their
respective dimensions are detailed in table 4.
Table 4. Specification of Wind turbine Rotors
Rotor model
nameRMN-00 RMN-01 RMN-02 RM-03 RMN-04
Rotor
diameter170mm 174mm 172mm 174mm 172mm
Hub
diameter25mm 25mm 25mm 25mm 25mm
Blade span 141mm 145mm 143mm 145mm 143mm
Blade root
chord32mm 32mm 32mm 32mm 32mm
Blade tip
chord13.7mm 7.46mm 10.58mm 7.46mm 10.58mm
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Swept area90792.02
mm2
95114.85
mm2
924940.87
mm2
95114.85
mm2
924940.87
mm2
Rotor weight 45gm 49gm 47gm 48gm 46gm
The above mentioned rotors were designed and selected for experimental
study. Since the tower and hub height is common to all the scale downed models a
common tower was deigned to hub height of 300mm.
2.2 Model fabrication
The fabrication for the project was done using various innovative
methods. The commercially available materials were used to make it economical
and composite materials were also used. Initially the wind turbine was taken into
two parts they were:
a. Wind turbine towerb. Wind turbine rotors
2.2.1 Wind turbine tower
The wind turbine tower was fabricated using mild steel. The tower was
designed using a hollow steel pipe of diameter 36mmwith length of 320mm and
flat steel plate of length 22mm and width 30mm with thickness of 3mm is used as
bottom stand. These two pieces are welded using Shielded metal arc welding.
Shielded metal arc welding (SMAW), also known as manual metal arc
(MMA) welding or informally as stick welding, is a manual arc welding process
that uses a consumable electrode coated in flux to lay the weld. An electric current,
in the form of either alternating current or direct current from a welding power
supply, is used to form an electric arc between the electrode and the metals to be
joined. As the weld is laid, the flux coating of the electrode disintegrates, giving
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off vapors that serve as a shielding gas and providing a layer of slag, both of which
protect the weld area from atmospheric contamination.
A horizontal shaft for the wind turbine rotor is fixed to frictional free ball
bearing in a 24mm hollow steel pipe of length 85mm. This hollow pipe is
horizontally fixed to the tower using nuts and bolts. The rpm sensor for reading the
number of rotation in the rotor is fixed above the horizontal pipe such that it faces
the small welded projection in the rotor shaft as shown in figure 4.
Fig 4. Welded projection & sensor Fig 5. completely fabricated tower
This tower is completely fabricated as shown in figure 5. The tower was
painted with primer and oil paint over the surface to reduce the drag produced by
them during the experiment which could possibly reduce the rotor wake in small
percent. The tower is fitted to the wind tunnel such that there is no vibration is in
the model during the running of the tunnel.
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2.2.2 Wind turbine rotors
The wind turbine rotors were fabricated using an innovative method Resin
Casting using wax dye. This method allowed us to produce the required number of
rotor blades in an economical manner without losing the quality equivalent to iron
dye casting method. The usage of composite materials allowed easing the
fabrication of the rotor and providing the required material properties like strength
and stiffness for the blades.
Initially one blade pattern was prepared using teak wood, since it meets the
surface finish requirement. While preparing the blade pattern, geometrical
requirements that are common to all five sets of rotor were taken into
consideration. The wooden pattern has been coated with olive oil due to the reason,
it provides enough. But we can use any oil which can act as good releasing agent
for the wax not to get stuck with the wooden pattern shown in Fig 6. Commercially
available candle wax is taken and melted by heating it around 450
C to550C. This
molten wax was poured in perfectly designed container which allows the wooden
pattern to accommodate in required orientation. The container was provided with
sufficient shrinkage allowances.
The container was kept on a bed of water which provides sufficient cooling in
all directions of the container walls. The water maintains the temperature limit
between 200C to 30
0C, which takes approximately 2 hours of curing time for the
wax. Finally the wax dye is removed from the container with great precautions.
The wax mould was cleaned using dry cotton which allows us to remove the
excessive oil (releasing agent). Then dimensions of the wax dye were measured in
order to match the required dimensions of the turbine blade shown in Fig 7.
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Fig 6. Wooden pattern of turbine blade Fig 7. Wax dye
. Since the small wind turbine blades require less strength when compared to
the large ones, we use resin and hardner which combined together alone provides
enough engineering property as required.
The composition taken to prepare the blade was resin LY566 and hardner HY
951[4]
, which was mixed in ratio of 10:1. This composite was mixed with small
quantity of chopped glass rowing. The glass fibers provide sufficient strength to
the composition.
The wax dye was coated with a small layer of releasing agent (oil) and the
excess was removed using dry cotton. The resin hardener composition is poured
into the wax dye and allowed to settle. Since we have designed a flat bottomed
airfoil small wind turbine blade, open mould technique [6] was followed. It was
even possible to cast in closed mould method, which could allow us to design
complicated pattern. The blade was allowed to settle in the dye for the respective
settling period at normal room temperature. After some duration the mould was
removed carefully using the additional projection provided in the dye without
affecting the main surface of the mould and wax dye.
Finally the composite blade has been taken out and the excessive composite
was removed. These blades fixed in 3 numbers in acrylic hub forming 5 sets of
wind turbine rotors.
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This fabrication method saved us lots of money when compared to the regular
iron casting method for this small quantity of blades. This fabrication can be
replaced by Plaster of Paris instead of wax, but the surface finish of wax is very
high, when compared to Plaster of Paris. The voids and cracks can affect the
surface of the mould, which is reduced in large scale for the wax dye. Thus making
it more reliable and good in quality.
Fig 8. Winglets in rotors Fig 9. Wind turbine rotors
These five sets rotors were drilled with hole in centre that allows us to fix in the
horizontal shaft in the tower. These composite small wind turbine rotors are shown
in figure 9.
2.3Experiment instruments
In our study we tested the models in subsonic suction type wind tunnel.
These wind tunnels are used for operations at very low mach number, with speeds
in the test section up to 400 km/h (~ 100 m/s, M = 0.3). The air is moved with a
propulsion system made of a large axial fan that increases the dynamic pressure to
overcome the viscous losses. In a real case the model is made moving and the
atmosphere is stable. But in the case of a wind tunnel the model is scaled and made
static in the wind tunnel and the air is in motion. Therefore the pressure and other
features of the model are calculated as per our requirements. The technical
specifications of the wind tunnel is shown in table 5.
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Figure 10. Image of a subsonic wind tunnel
Wind tunnel type Subsonic
Flow type Suction type
Test section area 0.37m2
Exit area 1.81m
2
Motor type 3 Phase, induction motor
Current 230 V, AC
Maximum motor rpm 1450rpm
Maximum wind speed
Table 5. Wind tunnel specifications
The non-contact type optical tachometer was used. It has a distance
difference indicating sensor. This sensor gets active when any metal surface gets
near its head and de-active when no metal is near. The signal from the sensor is
sent to the tachometer that measures the rate of change status. This rate of change
is converted to revolution per minute and indicated.
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Anemometer consisted simply of a glass U tube containing liquid, a
manometer, with one end bent in a horizontal direction to face the wind and the
other vertical end remains parallel to the wind flow If the wind blows into the
mouth of a tube it causes an increase of pressure on one side of the manometer.
The wind over the open end of a vertical tube causes little change in pressure on
the other side of the manometer. The resulting liquid change in the U tube is used
to calculate the wind speed.
2.4 Calculation of power coefficient:
The fabricated wind turbine tower was mounted inside the test section of
the wind tunnel. The wires of the sensor on the tower were passed through the
holes available in the test section and connected to the tachometer. The two ends
anemometer U- tube is connected to the respective pressure ports available in
wind tunnel. First the rotor RMN-00was fixed in the wind turbine tower inside
the wind tunnel and rpm and pressure difference were identified.
The rpm of the model was noted and the variation of the anemometer
reading in the wind tunnel is also noted respectively. Wind velocity in the wind
tunnel is calculated by applying the formulae
Tunnels wind velocity, V = 2*sqrt [(total pressure static pressure) / Air
density at room condition]
Where,
(Total pressurestatic pressure) is the difference in Anemometer multiplied with
value of 98.373.
The tip speed of the wind turbine rotors were calculated using formulae,
Tip speed, Vc = ( *rotor radius* models rpm) / 30
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The tip speed ratio was derived from ratio of tip speed to wind speed at rotor which
are,
Tip speed ratio, = ( tip speed, Vc / wind speed , V )
The wind turbine rotor coefficient of power is given by
Cp= Cpshmitzprofile lossuc.
Calculations of Cpshmitz for the rotor were obtained from the table, which has a
specific value for each tip speed ratio. The corresponding values are plotted in a
graph and extrapolated to get the required values.
Tip speed ratio Vs Cpshmitz
0.545
0.55
0.555
0.56
0.565
0.57
0 2 4 6 8 10 12
Tip speed ratio
Cpshmitz
Series1
Figure 11. Tip speed ratio vs Cpshmitz
The profile loss is given by,
profile loss = 1- /.
The tip loss is given by,
uc= 1-1.84/B.
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Where,
is the tip speed ratio and B is the blade number which denotes the number of
blades.
is the slide number for the rotor blade profile
The slide number is the ratio between the lift and the drag coefficient of the
particular aerofoil. The aerofoil selected for the turbine blade is NACA 4412
symmetrical aerofoil. The slide number for the airfoil at different wind speed is
obtained from the table and the values are extrapolated to get the slide number for
the different wind speeds.
Wind speed vs Slide number
0
5
10
15
20
25
30
35
40
0 2 4 6 8
Wind speed
Slidenumber
Series1
Figure 12. Wind speed vs Slide number
The maximum theoretical power of the wind turbine is given by,
Pmax
= 0.5**swept area*wind velocity3*0.59( Betz limit)
The actual power available in the wind turbine model is given by,
P = 0.5**swept area*wind velocity3*Cp
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Thus, the available power, power coefficient, tip speed ratio and rotor rpm were
tabulated for RMN-00. The same procedure is applied to the remaining RMN-01,
RMN-02, RMN-03 and RMN-04.
Model (RMN-01).
Rotor radius : 174mm,
Winglet height : 6.8mm,
Winglet curvature : 25% of winglet height.
Model
rpm
Vc=
nr/30
Wind
velocity,
V m/s
=Vc/V Power ,
watt
Coefficient
of power
200 3.644 2.82 1.290 1.3062 0.227
710 12.936 4.00 3.24 3.7273 0.336
960 17.491 6.32 2.76 14.729 0.319
1210 22.042 6.92 3.18 19.366 0.419
1470 26.783 7.48 3.58 24.373 0.418
1750 31.885 8.95 3.56 41.672 0.421
2010 36.622 9.79 3.73 54.779 0.425
2310 42.088 11.31 3.71 84.324 0.426
2650 48.283 12.64 3.81 117.86 0.428
3010 54.842 13.26 4.13 135.78 0.433
3230 58.850 13.85 4.24 154.92 0.435
3460 63.040 14.60 4.31 181.25 0.437
3860 70.329 15.49 4.54 216.45 0.439
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Cp vs rpm
0
0.05
0.1
0.15
0.2
0.25
0.30.35
0.4
0.45
0.5
0 1000 2000 3000 4000 5000
Coefficient of power
Figure 13. RMD-01 CP vs rpm
Model (RMN-02).
Rotor radius : 174mm
Winglet height : 3.4mm
Winglet curvature : 25% of winglet height.
Model
rpm
Vc=
nr/30
Wind
velocity,
V m/s
=Vc/V Power ,
watt
Coefficient
of power
410 7.47 4.00 1.86 3.64 0.316
690 12.57 4.89 2.56 6.68 0.371
750 13.66 6.92 1.97 18.92 0.364
1200 21.86 7.48 2.92 23.82 0.407
1450 26.41 8.00 3.30 29.14 0.416
1730 31.52 8.94 3.52 40.72 0.422
2030 36.98 9.79 3.77 53.53 0.425
2360 42.99 11.31 3.80 82.41 0.427
Table 7. RMN-02 power coefficient calculation
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Cp vs rpm
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 500 1000 1500 2000 2500
Cp vs rpm
Figure 14. RMD-02 CP vs rpm
Model (RMN-03)
Rotor radius : 172mm
Winglet height : 6.8mm
Winglet curvature : 12.5% of winglet height
Model
rpm
Vc=
nr/30
Wind
velocity,
V m/s
=Vc/V Power ,
watt
Coefficient
of power
510 9.18 4.00 2.295 3.727 0.339
750 13.5 4.89 2.755 6.843 0.376
1000 18.0 5.65 3.182 10.53 0.403
1250 22.5 6.92 3.247 19.36 0.412
1520 27.4 7.48 3.656 24.37 0.419
1780 32.1 8.00 4.005 29.81 0.424
2070 37.3 8.94 4.169 41.67 0.427
2390 43.1 11.3 3.802 84.32 0.427
2720 48.9 12.6 3.870 117.8 0.429
3080 55.4 13.5 4.088 145.2 0.437
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3280 59.0 14.1 4.175 164.7 0.436
3480 62.6 14.9 4.187 194.9 0.437
3890 70.0 16.0 4.376 238.5 0.439
Table 8. RMN-03 power coefficient calculation
Cp vs rpm
0
0.05
0.1
0.15
0.20.25
0.3
0.35
0.4
0.45
0.5
0 1000 2000 3000 4000 5000
Cp vs rpm
Figure 15. RMD-03 CP vs rpm
Model (RMN-04).
Rotor radius : 172mm
Winglet height : 3.4mm
Winglet curvature : 12.5% of winglet height
Model
rpm
Vc=
nr/30
Wind
velocity,
V m/s
=Vc/V Power ,
watt
Coefficient
of power
500 9.00 2.82 3.182 1.287 0.3276
700 12.6 4.00 3.150 3.643 0.3625
970 17.5 4.89 3.564 6.688 0.3899
1230 22.1 5.65 3.914 10.29 0.4127
1480 26.6 6.92 3.845 18.92 0.4191
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1780 32.0 8.00 4.005 29.14 0.4237
2070 37.3 8.94 4.165 40.72 0.4252
2380 42.8 10.5 4.049 67.40 0.4279
Table 9. RMN-04 power coefficient calculation
Cp vs rpm
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 500 1000 1500 2000 2500
Cp vs rpm
Figure 16. RMD-04 CP vs rpm
Model (RMN-00)
Rotor radius : 170mm
Without winglet
Model
rpm
Vc=
nr/30
Wind
velocity,
V m/s
=Vc/V Power ,
watt
Coefficient
of power
400 7.12 2.82 2.51 1.256 0.3158
530 9.43 4.00 2.35 3.552 0.3420
770 13.7 4.89 2.78 6.521 0.3732
1020 18.2 5.65 3.21 10.04 0.4043
1280 22.7 6.92 3.28 18.45 0.4119
1550 27.6 7.48 3.68 23.25 0.4285
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1840 32.7 8.00 4.09 28.41 0.4231
2140 38.1 8.94 4.25 39.71 0.4264
2440 43.4 11.3 3.83 80.35 0.4271
Table 10. RMN-00 power coefficient calculation
Cp vs rpm
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 500 1000 1500 2000 2500 3000
Cp vs rpm
Figure 17. RMD-00 CP vs rpm
The model RMD-03 was found to be the efficient rotor among other models.
Thus, the RMD-03 was selected for further investigation in noise comparison and
rotor wake study.
2.5 Experimental methodology for noise comparison
An high sound recognizing microphone were installed over the surface of test
section. The wind tunnel was run to a specific wind velocity and noise produced
was plotted in decibels (dB) in 32bit with respective to time. The rotor RMD-03
was mounted and noise level was plotted same specific wind velocity. Now the
rotor without winglet RMD-00 was replaced with RMD-03 and the noise level was
plotted. The graphs were compared and studied.
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Figure 18. of noise level in 32bit vs time a) test section b) RMD-03 c) RMD-00
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2.6 Experiment methodology for Rotor wake study
A wake is the region of disturbed flow downstream of a solid body moving
through a fluid, caused by the flow of the fluid around the body. In wind turbine
this flow is found behind the rotor.
The model RMN-003 was mounted inside the wind tunnels test section.
The grid formed with single row of 14 pitot tubes and 2 static tubes as shown in
figure was placed inside the test section. The grid was moved to various length of
rotor diameter like 1D, 1.5D, 2D etc horizontally behind the wind turbine rotor.
The row in the grid was moved vertically to 7 positions giving us the wind speed at
various positions behind the rotor. Thus the wake distribution behind the rotor was
identified. The flow structure in the wake region has been investigated with the
wind tunnel experiment at constant wind speed especially paying attention to the
scale effects of the wind turbine model.
The wind velocity of 5.86m/s was created inside the test section ignoring
the losses due to boundary layer effect. The virtual test section of 1.87ft X 1.87ft
was taken into consideration from 2ft X 2ft test section to avoid the disturbance in
the wind flow caused by the walls of test section.
The wake is identified by the variation of pressure at the locations the
respective locations. This variation is shown in the pressure distribution scale
connected to the pitot and static tubes in the grid.
This pressure variation is converted to wind velocity using the formulae (1)
and tabulated to their respective positions as shown in tables 11,12,13,14 and 15.
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The tabulated wind velocities are represented in 3Dgraphs with vertical and
horizontal location with respective wind speed.
Figure 19. Velocity distribution at 1D distance behind rotor
Figure 20. Velocity distribution at 1.5D distance behind rotor
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Figure 21. Velocity distribution at 2D distance behind rotor
Figure 22. Velocity distribution at 2.5D distance behind rotor
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Figure 23. Velocity distribution at 2.75D distance behind rotor
The wake study showed that wind flow variation becomes steamline behind the
rotor after the distance 2.75D of the wind turbine rotor at wind speed of5.86m/s. thevariation of the velocity flow due to rotor and tower was alone considered during this
study.
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3. RESULTS AND DISCUSSION
3.1ResultThe comparison of the models RMD-01, RMD-02, RMD-03, RMD-04 and
RMD-00 with respective to their rpm and coefficient of power is tabulated in
table 16.
RMD-01 RMD-02 RMD-03 RMD-04 RMD-00
Rpm Cp rpm Cp Rpm Cp rpm Cp rpm Cp200 0.227 410 0.316 510 0.339 500 0.3276 400 0.3158
710 0.336 690 0.371 750 0.376 700 0.3625 530 0.342
960 0.319 750 0.364 1000 0.403 970 0.3899 770 0.3732
1210 0.419 1200 0.407 1250 0.412 1230 0.4127 1020 0.4043
1470 0.418 1450 0.416 1520 0.419 1480 0.4191 1280 0.4119
1750 0.421 1730 0.422 1780 0.424 1780 0.4237 1550 0.4285
2010 0.425 2030 0.425 2070 0.427 2070 0.4252 1840 0.4231
2310 0.426 2360 0.427 2390 0.427 2380 0.4279 2140 0.4264
2650 0.428 2720 0.429 2440 0.4271
3010 0.433 3080 0.437
3230 0.435 3280 0.436
3460 0.437 3480 0.437
3860 0.439 3890 0.439
Table 16. comparison of Cp and rpm of RMD-00,01,02,03,04
The graphical representation of the comparison of rpm and coefficient of power
of the various models RMD-00, RMD-01, RMD-02 ,RMD-03 and RMD-04 are
shown in figure 24 and 25 respectively.
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Figure 24. Cp comparison of RMD-00, 01, 02, 03 and 04
Figure 25. rpm comparison of RMD-00, 01, 02, 03 and 04
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The results of the experiment indicated in the table 16 and figures 24,25 shows that
the model RMD-01 and RMD-03 with 6% winglet height in common and with a
curvature of 12.5% and 25% of radius were the efficient models. In which the RMD-
03 indicated higher rpm, lower staring wind speed and coefficient of power than
RMD-01.
The noise produce by the rotor RMD-03 with winglets of 6% height and 12.5%
radius of curvature was lower than the rotor RMD-00 without winglets.
The wake created by the rotor RMD-03 with winglet settled at an distance of
2.75D of the rotor.
4. CONCLUSION
The present study indicates a strong relation between winglet height, rotation
rate (rpm), curvature radius and power co-efficient. Winglet added rotor models gives
increase in power coefficient. An increase in winglet height and optimum radius of
curvature shows lower starting wind velocity and increase in rotational speed even in
low wind speeds allowing overall increase in power coefficient and reduction in noise
due to vibration. The wake study of the wind flow behind the rotor allowed us to find
the location were the wind get stream lined again. This could positively increase the
effective utilization of area in an wind farm in which large number of wind turbines
are installed together to satisfy higher energy needs. It is also possible that winglet
added wind turbine is best suited for remote areas, where wind power available is less.
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