comparison of power output by airfoil shaped 3-blade and 4...
TRANSCRIPT
Comparison of Power output by Airfoil shaped 3-Blade and 4-Blade
Vertical Axis Wind Turbine for the local wind conditions
MADHUSUDAN.M.A1,
Lecturer, A.P.S. College of Engineering, Bangalore
MANJUNATH. B2
Lecturer, A.P.S. College of Engineering, Bangalore
Abstract: With depletion of fossil fuels, there is increased dependency on non-conventional energy
sources for generation of electricity. Conversion of
wind energy to electricity is one among them. While
large wind farms are already in existence to produce
several megawatts of power, small roof-top wind
energy convertors are gaining popularity for individual
customers. This paper contains a study of two small
vertical axis wind turbine for generation of electricity.
The selected NACA 6409 airfoil as the wind turbine
blades showed that the optimized angle of attack for
the airfoil (blade) was 80 for the design maximum wind
speed of 15 m/s. Assuming the wind turbine location at Bangalore, at an elevation of 15 m from the ground
level was assumed to achieve the minimum cut in wind
speed of 5 m/s required. By using double multiple
stream-tube model through SCILAB code, the solidity,
Tip Speed Ratio and number of blades were optimized
through an iterative process to compare the power
coefficients, and the power developed by the wind
turbines were estimated. The results culminated in a
configuration which had 3-blades with a solidity of
0.45 and Tip Speed Ratio of 6.
Key Words: Airfoil, Angle of attack, coefficient of lift, coefficient of drag, Solidity, Tip Speed Ratio,
VAWT, SCILAB code.
Introduction: Wind power is an alternative to fossil
fuels, is inexhaustible, widely distributed, clean,
renewable, and produces no green house gas emissions
during operation. Exploitation of wind energy is not
new and dates back to 200 B.C when Persians used
“wind wheels” for grinding food grains. Wind mills
first appeared in Europe during the middle ages and by
the 14th Century, Dutch wind mills were used to drain
excess water from the river basins [1]*.
The effort of over a millennium of windmill development culminated in “wind turbines” for
generating electrical power. The first electricity-
generating wind turbine was a battery charging
machine installed in 1887 by James Blyth of Scotland.
A few years later, American inventor Charles Brush
built the first automatically operated wind turbine for
electricity production.
*Number within the parenthesis indicates serial
number of reference listed at the end of the report.
Today, however, new wind machines are beginning to
appear on the landscape, as windy rural areas tap a
unique opportunity to benefit from wind power.
Modern wind turbine technology now makes it possible
to generate cost-effective, clean, renewable electricity
on a scale ranging from a single wind turbine for an
individual landowner up to large, utility-scale "wind
farms." Declining costs and improving technology are
quickly making electricity generated from wind energy
competitive with all types of non-renewable fuels, like
new coal-fired regeneration.
Worldwide there are now over two hundred thousand
wind turbines operating with installed capacity of
2,82,482 MW as of end 2012. The major capacity
sharing is by the European Union (1,00,000 MW);
United States (50,000 MW) and China (50,000 MW).
India has an installed wind power capacity of January
2013 and account for 6.5% of world total wind power
capacity. Wind power accounts for 8.5% of India’s
total installed power capacity, and it generates 1.6% of
the country’s power. With the advent of technology,
interest in small wind turbines (300 to 10000 W) is increasing for roof top application either independently
or in combination with solar photovoltaic power
generators.
1. Wind Power Development in India:
The development of wind power in India began in the
1990s, and has significantly increased in the last few
years. Although a relative newcomer to the wind
industry, India has the fifth largest installed wind
power capacity in the world according to recent
survey. According to “Global Wind report 2012-13”,
wind power generation in India is 18421 MW, which
accounts for 6.5 % of total wind power developed in the world. Wind power accounts for 8.5 % of India’s
total installed power capacity, and it generates 1.6 % of
the country’s power [2].
As per recent survey the installed capacity of wind
power in India was 18421 MW, states which are the
main source of wind power in India are as listed in
Table 1.1.
Ministry of New and Renewable Energy (MNRE) has
announced a revised estimation of the potential wind
resource in India from 49,130 MW assessed at 50m
Hub heights to 102,788 MW assessed at 80m Hub height. The wind resource at higher Hub heights that
are now prevailing is possibly even more.
Table 1.1 List of India’s prominent wind power
developing states
States Installed
Capacity (MW)
Tamil Nadu 7154
Gujarat 3093
Maharashtra 2976
Karnataka 2113
Rajasthan 2355
Madhya Pradesh 386
Andhra Pradesh 435
Kerala 35.1
Orissa 2
West Bengal 1.1
Others 3.20
2. How Wind Turbines Work: The wind imposes two driving forces on the blades of a
turbine; lift and drag. A force is produced when the wind on the suction side of the airfoil must travel a
greater distance than that on the pressure side. The
wind traveling on the suction side must travel at a
greater speed than the wind traveling along the
pressure side. This difference in velocity creates a
pressure differential. On the suction side, a low-
pressure area is created, pulling the airfoil in that
direction. This is known as the Bernoulli’s Principle.
Lift and drag are the components of this force vector
perpendicular to and parallel to the apparent or relative
wind, respectively. By increasing the angle of attack, as shown in Fig. 2.1,
the distance that the suction side air travels is
increased.
Lift and drag forces can be broken down into
components that are perpendicular (thrust) and parallel
(torque) to their path of travel at any instant. The
torque is available to do useful work, while the thrust is
the force that must be supported by the turbine’s
structure.
Fig. 2.1 Forces acting on a wind turbine blade
2.1 Wind Power
Power of the wind is proportional to air density, area of
the segment of the wind being considered, and the
natural wind speed. The relationship between the above
variables is provided in equation 2.1.
3
2
1 AVPW
2.1
Where
Pw: power of wind (W)
ρ: air density (kg/m3)
A: area of a segment of the wind being
considered (m2) V∞: Undisturbed wind speed (m/s)
At standard temperature and pressure (STP = 273.15K
and 101.3 kPa), 3647.0 AVPW 2.2
A turbine cannot extract 100% of winds energy
because some of the winds energy is used in pressure
changes occurring across the turbine blades. This
pressure changes causes a decrease in velocity and
therefore usable energy. The mechanical power that
can be obtained from the wind with an ideal turbine is
given by equation 2.3.
3
2716
2
1 AVPm 2.3
Where
Pm: mechanical power (W)
Fig. 2.3 Area swept by a vertical axis wind turbine
In equation 2.3, the area, A, is referred to as the swept
area of the turbine shown in Fig. 2.3. For vertical axis
wind turbine, this area depends on both the diameter
and turbine height (blade length). For an H-rotor
vertical axis wind turbine swept area is represented by
equation 2.4.
DHA 2.4
Where
As: swept area (m2)
D: diameter of the turbine (m)
H: height of the turbine (m)
The constant 16/27 = 0.593 from equation 2.3 is
referred to as the Betz coefficient. The Betz coefficient
conveys that 59.3% of power in the wind can be
extracted in the case of an ideal turbine. However, an
ideal turbine is a theoretical case. Turbine efficiency in
the range of 35-40% is very good, and this is the reason
for low power output of the wind turbine [2].
2.2 Principle of Aerodynamics
The wind imposes two driving forces on the airfoil
shaped blades of a turbine lift (L) and drag (D). A force
is produced as the wind on the suction side of the
airfoil must travel a greater distance than that on the
pressure side. The wind travelling on the pressure side
is traveling at a lower speed than the wind travelling
along the suction side as illustrated in Fig. 2.4. This
difference in velocity creates a pressure differential. On
the suction side, a low-pressure area is created, pulling the airfoil in that direction. This is known as the
principle of aerodynamic lift. Lift and drag are the
components of this force vector perpendicular to and
parallel to the apparent or relative wind, respectively.
By increasing the angle of attack (α), the distance that
the suction side air travels is increased. This increases
the velocity of wind on the suction side and
subsequently the lift increases as the pressure
decreases. The component of resultant force of lift and
drag rotates the blade, thus torque is developed on the
blade.
Fig. 2.4 Aerodynamic lift
Torque developed at a point on wind turbine blade
depends on the force at that point on the wind turbine
blade and distance of that point on the blade from the
shaft axis which is the axis of rotation. Force at a point
on the blade is the product of pressure difference at that
point on the blade and area of the blade. Thrust on the
wind turbine blades must be supported by the shaft of the wind turbine.
Fig. 2.5 Pressure difference on the airfoil surfaces
Lift and drag forces acting on the airfoil can be
calculated using the equations 2.5 and 2.6 respectively.
Where,
CL = Coefficient of lift
CD = Coefficient of drag ρ = Density of air (kg/m3)
Aw = Wing area (m2)
V = Velocity of air (m/s)
s = span (m)
c = chord (m)
3. Airfoil selection
For the survey of the airfoil, National Advisory
Committee for Aeronautics (NACA present NASA) is
the source. For the airfoil to be selected as a blade for
vertical axis wind turbine it should have maximum
coefficient of lift and minimum coefficient of drag.
That is the airfoil should have maximum lift to drag
ratio. After a survey of several airfoils the NACA 6409 airfoil was selected. The coordinates and profile of the
NACA 6409 airfoil is as shown in Table 3.1
Fig. 3.1 shows the profile of NACA 6409 airfoil which
is generated using MS excel, the coordinates of the
airfoil has been collected from NACA official website,
www.airfoiltool.com. The coefficient of lift (CL) and
coefficient of drag (CD) for various angles of attack (α)
have been obtained from the same source for various
angles of attack, and plotted in Fig 3.2.
Table 3.1 NACA 6409 airfoil coordinate
Profile x/c y/c
Suction
side
300 0
287.28 3.852
238.941 16.134
211.824 21.459
197.13 23.833
166.289 27.906
134.52 30.456
118.77 31.08
87.945 30.258
59.864 26.622
26.94 17.667
Pressure
side
0 0
22.248 -3.24
51.771 -0.357
76.494 2.187
118.857 4.917
149.604 5.613
195.579 5.64
224.184 4.902
249.669 3.723
278.54 1.728
292.509 0.66
300 0
Fig. 3.1 Profile of NACA 6409
Fig. 3.2 shows how the ratio of CL/CD varies with
respect to angle of attack. The CL/CD ratio is almost
constant between 30 and 90.
Fig.3.2 Variation of CL and CD for NACA 6409 airfoil
with angle of attack for different Reynolds number
4. Wind conditions in Bangalore
Selection of Bangalore as the place of application, the wind conditions for Bangalore over a year was studied
[25].
Fig. 4.1 Annual wind velocities for Bangalore [25]
Fig. 4.1 shows the variation of wind velocity in
bangalore in a year, it indicates average annual wind
velocity in bangalore to be 3.2 m/s, and the wind
velocity is high in the months of june, july and august.
Table 4.1 Assumed mean wind conditions for
Bangalore
Quantity Value
Temperature 26°C
Dynamic Viscosity of Air 1.84E-5 kg/ms
Density of Air 1.184 kg/m3
Pressure 101325 Pa
Mean wind velocity at ground level 3.2 m/s
The Table 4.1 shows calculated mean temperature, dynamic viscosity, pressure, density and velocity of air
at Bangalore. For the calculation of pressure and
density of air the vertical axis wind turbine is assumed
to be placed at an elevation of 15 m above the ground
level. The viscosity of air has been calculated using the
Sutherland’s Formula, which is expressed as follows
[26]:
Where:
= is a reference temperature (K)
= is the viscosity at the reference temperature
(kg/ms)
S = is the Sutherland temperature (K)
For Air,
µref = 1.716 X 10-5kg/ms
Tref = 273.15 K
S = 110 K C1= 1.458 X 10-6 kg/msK2
Density of air can be calculated using the formula,
Where
ρ = Density, kg/m3
P = Pressure, Pa
T = Temperature, K
R = Gas constant = 287.05 J/kg-K
5. Power Calculation
Power calculation for a vertical axis straight blade
wind turbine consists of following. 1: Calculation of forces acting on the wind turbine by
numerical method.
2: Estimation of the Tip Speed Ratio (TSR), and
solidity of the wind turbine.
3: Estimation of power developed by the wind turbine.
-10 0
10 20 30 40
0 100 200 300 400
Series1
0
20
40
60
80
100
120
140
160
0 5 10 15
CL/
CD
α (degrees)
CL/CD Vs α
RE=50000
RE=100000
RE=200000
RE=500000
RE=1000000
0
1
2
3
4
1 2 3 4 5 6 7 8 9 10 11 12
Win
d V
elo
city
(m
/s)
Month
Annual wind velocity in Bangalore
wind velocity variation average wind velocity
Table 5.1 wind turbine specification
Specification Value
Rotor Diameter (D) 2 m
Height of the Blade (H) 1.5 m
Swept area of Blades (A) 2.25 m2
Density of air (ρ) 1.184 kg/m3
Number of blades (N) 3
Wind free stream velocity(V∞) 15 m/s
Table 5.1 indicates the important specifications of the
vertical axis wind turbine which have been arrived at
through numerical calculations.
5.1 Details of the Airfoil (Blade)
The blades used in the wind turbine are of the airfoil
shape. The airfoil that has been selected for the wind
turbine is NACA 6409. The specifications of the airfoil
are as shown in Table 5.2.
Table 5.2 Specifications of vertical axis wind turbine
blade
Specification Value
Chord length of the airfoil (c) 0.3 m
Length of the blade (H) 1.5 m
Surface area of the blade (AW) 0.45 m2
The vertical axis wind turbine can be controlled by stall
or pitch control. The mathematical modelling of the
vertical axis wind turbine is considered in the next
section using Blade Element Momentum and Double –
Multiple stream tube modelling.
5.2 Double-Multiple Stream Tube Model
Fig. 5.1 Double multiple stream tube model [15]
In double-multiple stream tube model, rotor area is
divided into two regions, upstream and downstream as
shown in Fig. 5.1 where air flows through two actuator
disks models in a tube. The actuator disk model is an
imaginary infinitesimal thin rotor with infinite number of blades and its only effect is to drop pressure without
changing wind speed in the rotor area. For each tube
the 1-D momentum theory is used to relate the rotor
upstream and downstream velocities by defining an
axial induction factor. For the upstream
and the downstream
, the local upstream
velocity, V, the equilibrium velocity, Ve, and the
downstream, , will differ from the free stream
velocity, V∞, by:
Fig. 5.2 Relative wind speed vectors in upstream and
downstream sections of H-rotor vertical axis wind
turbine [15]
In these relations, and are the axial induction
factors in the upstream and the downstream regions,
respectively (always ). is the equilibrium velocity in the joining region of both semi tubes. As
shown in Fig. 5.2, the local relative wind speed for the
upstream section of the rotor can be determined by:
Where
represents the local tip speed ratio.
The angle of attack is also determined by:
By combining the blade element theory and the
momentum theory for each stream tube, the induction
factor, u for the upwind section is calculated from:
in which is given by:
Where is called the solidity factor
which is measured by blade swept area divided by the
rotor area. Also CN and CT are the coefficients of
normal and tangential components of the resultant
force respectively. These forces coefficients are related to the angle of attack α, and the lift and drag
coefficients for each airfoil section as follows:
The normal force, , and tangential force, ,
component of the resultant force in the upstream
section of the rotor, as shown in Fig 5.3, are
determined by:
Where is the blade projection area, with c as the chord length and H as the height of rotor. The
rotor sweep area is defined by , with R as
the radius of the rotor.
Adding up the moment of tangential component of
the resultant force about the rotor center for each
stream tube, the upstream contribution to total torque
obtained as follows:
Where ρ is the air density. Thus the power coefficient
for the upstream section can be written as:
Fig. 5.3 Forces exerted on an airfoil section of a wind turbine blade [15]
This is repeated for downstream section with the
equilibrium velocity, given by equation 5.2, as the free
stream for the second actuator disk in the downstream
section of the stream tube. The local relative air
velocity and the angle of attack in the downstream
section are obtained by:
Similarly, by combining the blade element theory and
the momentum theory for each stream tube, one can
determine the downstream induction factor, from:
Where is given by:
In the above relation, and are the coefficients of the normal and tangential components of the
resultant force in downstream section respectively,
which are related to the angle of attack, , and the lift
and drag coefficients as follows:
The normal, and tangential, components of the
resultant force in demonstration section of the rotor are
determined by:
Adding up the moment of tangential component of the
resultant force about the center for each stream tube, the downstream contribution to total torque is obtained
as follows:
Thus power coefficient for the downstream
section can be determined by:
Adding up the power coefficient in upstream section,
and in downstream section, , the total power
coefficient is obtained for one cycle as follows:
The aim is to achieve the maximum power coefficient
at rated speed.
5.3 Numerical Calculation
The discussed double – multiple stream tube models
were programmed in SCILAB routines. In order to
calculate the induction factors, and , an iterative
method is used. In this method, the upstream induction
factor u is initially taken to be unity. Applying relations
5.4, 5.5, 5.8, 5.9 and substituting in equation 5.7
determines . A new induction factor u is then
calculated from equation 5.6. This procedure is iterated
to calculate a new induction factor until the difference
between two consecutive values of the induction
factors converges to an error band less than 0.01. Next,
the final value of induction factor in upstream section
is used as initial guess for determining the induction
factor in downstream section. The above algorithm
is repeated for downstream section until convergence is
achieved. The remaining parameters are subsequently
determined from the relations explained in the previous section.
5.4 Equations for Coefficient of Lift and Drag
The airfoil section NACA6409 is chosen due to the
relatively high lift to drag ratio of 150 at the angle of
attack of 8° for the design of this specific H-rotor
vertical axis wind turbine. Lift and drag coefficients
with respect to angle of attack for this airfoil is
obtained by curve fitting two parabolic functions, as
follows:
5.5 airfoil section
The airfoil section NACA6409 is chosen due to the relatively high lift to drag ratio of 150 at the angle of
attack of 9° for the design of this specific H-rotor
vertical axis wind turbine. Lift and drag coefficients
with respect to angle of attack for this airfoil is
obtained by curve fitting two parabolic functions, the
equation are as follows:
Fig 5.4 Coefficient of tangential Force versus
azimuthal angle for 3-blades
Fig 5.4 shows how the coefficient of tangential force
varies with respect to the azimuthal angle which has
been calculated by the numerical procedure.
5.6 Analysis of 3-blade wind turbine
5.6.1 Aerodynamic results
In the design of a straight blade vertical axis wind
turbine, one of the factors which play a very important
role in the power generation of a wind turbine is the
angle of attack (α), the airfoil profile used for the wind
turbine is NACA6409, according to the airfoil data the
maximum lift to drag ratio achieved by the airfoil is at
an angle of attack of 8°. The angle of attack for the
wind turbine blade calculated by numerical approach is
as shown in the Fig 5.5, the figure shows the variation
angle of attack of the turbine blade with respect to azimuthal angle during the upstream section.
(a)
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 100 200 300 400
Co
eff
icie
nt
of
Tan
gen
tial
Fo
rce
(C
T)
Azimuthal Angle (θ)
TSR=6,σ=0.45 for 3 blades
TSR=6,σ=0.45
0
2
4
6
8
10
12
14
16
-100 -50 0 50 100
An
gle
of
Att
ack
(α)
Azimuthal Angle (θ)
σ = 0.45
TSR=6
TSR=5
TSR=4
(b)
Fig 5.5(a),(b) angle of attack variation with azimuthal
angle for σ=0.45, and 0.6
Fig 5.6 variation of coefficient of lift by drag ratio with
respect to azimuthal angle
5.6.2 Forces acting on the wind turbine
Fig 5.7 variation of coefficient of tangential force with
the azimuthal angle for σ=0.45
Fig 5.8 variation of coefficient of tangential force with
the azimuthal angle for σ=0.6
Tangential force is the most important component of the wind turbine, it varies as the wind
turbine rotates, and the variation of coefficient of
tangential force with the azimuthal angle, has been
estimated for two solidities 0.45 and 0.6 in upstream
and downstream sections, as shown in the figures 5.7
and 5.8 respectively.
Fig 5.9 variation of coefficient of normal force with the
azimuthal angle for σ=0.45
Normal force which perpendicular with respect
to tangential force, the normal force also varies as the
turbine rotates. The variation of normal force
coefficient with the azimuthal angle has been estimated
for two solidities 0.45 and 0.6 in upstream and
downstream sections, as shown in the figures 5.9 and
5.10 respectively.
0
2
4
6
8
10
12
14
16
-100 -50 0 50 100
An
gle
of
Att
ack
(α)
Azimuthal Angle (θ)
σ = 0.6 TSR=6
TSR=5
TSR=4
0
10
20
30
40
50
60
70
-100 -50 0 50 100
CL/
CD
Azimuthal Angle (θ)
σ = 0.45 TSR = 4
TSR = 5
TSR = 6
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
-100 0 100 200 300
Co
effi
cien
t o
f Ta
nge
nti
al F
orc
e
Azimuthal Angle (θ)
σ = 0.45
TSR=4
TSR=5
TSR=6
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
-100 0 100 200 300
Co
eff
icie
nt
of
Tan
gen
tial
Fo
rce
Azimuthal Angle (θ)
σ = 0.6 TSR = 6
TSR = 5
TSR = 4
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
-100 0 100 200 300
Co
eff
icie
nt
of
No
rmal
Fo
rce
Azimuthal Angle (θ)
σ = 0.45 TSR=4
TSR=5
TSR=6
Fig 5.10 variation of coefficient of normal force with
the azimuthal angle for σ=0.6
Variation of coefficient of tangential force for 3-blade
vertical axis wind turbine with the azimuthal angle is as
shown in the Fig 5.11. The sum and average of the coefficient of tangential force for the wind turbine has
been calculated and is as shown in the Fig 6.12, it
shows that the average coefficient of tangential force is
0.2557.
Fig 5.11 variation of coefficient of tangential force
with the azimuthal angle for σ=0.45 and TSR=6, for 3-
blades
Fig 5.12 variation of coefficient of tangential force
with the azimuthal angle for σ=0.45 and TSR=6, for 3-
blades, with sum, and average of 3-blades
5.7 Analysis of 4-blade wind turbine
5.7.1 Forces acting on the wind turbine
Fig 5.13 variation of coefficient of tangential force
with the azimuthal angle for σ=0.6 and TSR=6, for 4-
blades
Numerical analysis was conducted for a 4-blade
vertical axis wind turbine by using the similar
calculation as used in case of 3-blade wind turbine,
with assumption of specification shown in Table 6.3, the results showed that there was an increase in the
average coefficient of tangential by 30%, i.e., 0.334,
which is as shown in figure 5.14.
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
-100 0 100 200 300
Co
eff
icie
nt
of
No
rmal
Fo
rce
Azimuthal Angle (θ)
σ = 0.6
TSR = 6
TSR = 5
TSR = 4
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
-100 0 100 200 300
Co
effi
cien
t o
f ta
nge
nti
al fo
rce
Azimuthal angle (θ)
TSR=6, σ=0.45
blade1
blade2
blade3
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
-100 0 100 200 300
Co
eff
icie
nt
of
Tan
gen
tial
fo
rce
Azimuthal angle (θ)
TSR=6, σ=0.45
blade1
blade2
blade3
sum
average
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
-100 0 100 200 300
Co
eff
icie
nt
of
tan
gen
tial
fo
rce
Azimuthal angle (θ)
TSR=6,σ=0.6
blade 1
blade2
blade3
blade4
Table 5.3 Specifications for 4-blade vertical axis wind
turbine
Specification Value
Rotor Diameter (D) 2 m
Height of the Blade (H) 1.5 m
Swept area of Blades (A) 2.25 m2
Density of air (ρ) 1.184 kg/m3
Number of blades (N) 4
Wind free stream velocity(V∞) 15 m/s
Solidity (σ) 0.6
Tip Speed Ratio-TSR (λ) 6
Fig 5.14 variation of coefficient of tangential force
with the azimuthal angle for σ=0.6 and TSR=6, for 3-
blades, with sum, and average of 4-blades
Solidity of the wind turbine increases when the
analysis is conducted for the 4-blade vertical axis wind
turbine.
5.8 Power Co-efficient for 3-blade wind turbine
Fig 5.15 variation of coefficient of tangential force
with the azimuthal angle for σ=0.45 and
It is found that from Fig 5.15, the maximum power
coefficient that can be obtained from the wind turbine
is 0.1217, which is during up-stream.
6. Plan for application of the wind turbine for
a rooftop wind form
The case study was to plan a wing farm over the
mechanical department building in APS College of Engineering, Bangalore. The height of the building is
15 m, the plan is to plant the wind turbine of
specifications as shown in the paper.
According to the area available over the roof of the
building, the number of wind turbines that can be
placed was decided, and the type of arrangement of the
wind turbine was found to be staggered type of
arrangement, arrangement is such that there should not
be any obstruction for the wind flow for all the wind
turbines.
The wind turbines were planned to plant in such a way
that the first set of wind turbines were planned to be planted at an elevation of 15 m above the ground level,
and the second set of wind turbine were planned to be
planted at a elevation of 15 m above the ground level.
The specifications of the wind form over the building
are as shown in the table 6.1.
Table 6.1 Wind Form Specifications
Sl.no Specifications value
1. Area of wind form over the
building
1173.68
SMT
2. Number of wind turbines that can
be placed over the building
33 units
3. Elevation of the 1st set of wind
turbines
15 m
4. Elevation of the 2nd set of wind
turbines
17 m
5. Number of wind turbines in 1st set
16 units
6. Number of wind turbines in 2nd
set
17 units
The plan of the wind form over the building is as
shown in the Fig. 6.1. The circles with number inside it
indicates the wind turbine, it’s a total of 33 wind
turbines.
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
-100 0 100 200 300
Co
eff
icie
nt
of
tan
gen
tial
fo
rce
Azimuthal angle (θ)
TSR=6, σ=0.4
blade 1
blade2
blade3
blade4
sum
average
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
-90 -45 0 45 90 135 180 225 270
λ=6,σ=0.45
TSR=6,SIGMA=0.45
θ
CP
Fig 6.1 Wind Form Plan
6.1 Power calculation
The capacity of wind form was evaluated, depending
on the local wind speed availability over the year. The
total number of wind turbines planed to be placed over
the building is 33 units. The power capacity of the
wind form is as shown in the Fig. 6.2.
Fig. 6.2 Total Power that can be harnessed by
the wind form over the year.
Fig. 6.2, shows the mechanical wind power that can be
harnessed by the wind form over the year, there are two
curves, 16WT, 15m indicates the power that can be
harnessed by the 1st set of 16 wind turbines placed at an
elevation of 15m above ground, and 16WT, 15m
indicates the power that can be harnessed by the 2nd set
of 17 wind turbines placed at an elevation of 17m above ground. The total power that can harness over
the year by the wind turbine is 4927.248 kWh. The
power required to power the building that is as shown
in Fig. 7.1, is 30 kWh, if the wind speed remains
constant throughout the day the wind form can harness
13.5 kWh. Thus, the wind form can harness around
45% power requirement for the building. Thus, if this
plan is successfully implemented, it could be very
helpful to overcome the power crises in recent days.
10. Conclusion
An attempt has been made to establish the design
methodology for an H-Rotor vertical axis wind turbine.
As torque is provided by forces acting on profiled
turbine blades, an airfoil profile according to NACA
6409 was chosen for the blade cross section. Basing on
yearly average wind conditions for Bangalore, a flow
analysis was conducted for the turbine blades using the
CFD code COMSOL. The results indicated an optimum angle of attack of 80 for selected profile.
The number of blades, Tip Speed Ratio and blade
solidity were optimized through an iterative procedure
using the open source SCILAB code. It was observed
that for Bangalore conditions where the average ground
wind speed is about 3.2 m/s, the turbine needs to be
located at an elevation of 15 m to achieve a wind speed
of 4 m/s which is more than the required minimum cut-in wind speed of 4 m/s.
The turbine has a configuration that has 3-blades at a
Tip Speed Ratio of 6 and blade solidity of 0.45.
Application of the wind turbine to wind form of 33
units of wind turbine on the roof top of a building of
area 1173.68 SMT, it can harness 13.5 kWh per day
assuming constant wind speed though out the day and it can harness around 45% power requirement for the
building.
10.1 Scope for future work
Since availability of wind power is not assured all the
time, it is advantageous to build wind-solar hybrid
power generators so that a minimum amount of power
availability can be assured always. A solar photovoltaic
system in combination with the proposed wind turbine will be an ideal combination to meet power needs of
individual urban household and small communities.
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