International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 01, January 2019, pp. 837–846, Article ID: IJMET_10_01_087
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=01
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
PERFORMANCE EVALUATION OF SAVONIUS WIND
TURBINE BASED ON A NEW DESIGN OF BLADE SHAPE
Salih Meri AR
Faculty of Mechanical and Manufacturing Engineering, University Tun Hussein Onn Malaysia
(UTHM), Parit Raja, Batu Pahat, Johor, Malaysia
Iraqi Cement State Company, Ministry of Industry and Minerals, Baghdad, Iraq
Hamidon Bin Salleh B
Faculty of Mechanical and Manufacturing Engineering, University Tun Hussein Onn Malaysia
(UTHM), Parit Raja, Batu Pahat, Johor, Malaysia
Mohammed Najeh Nemah, Balasem A. Al-Quraishi
Engineering Technical College-Najaf, Al-Furat Al-Awsat Technical University, 32001, Najaf,
Iraq.
Nor Zelawati Binti Asmuin
Faculty of Mechanical and Manufacturing Engineering, University Tun Hussein Onn Malaysia
(UTHM), Batu Pahat, Johor, Malaysia.
ABSTRACT
It is known that traditional sources of energy negatively affects the health and state
of the environment. The consumption of fossil fuels in all elements of life leads to the
export of carbon dioxide to the atmosphere contributing to global warming. Thus, the use
of wind energy to generate energy is a practical alternative between all renewable
sources. This paper presents the parameters effect of the blade shape and the overlap
ratio on the performance efficiency of the elliptical Savonius wind turbine. A new model
of Savonius blade has been designed by changing the inner surface of the concave blade
with overlap ratio of (0.2). The new model is printed using 3D-printer technology for
experimental testing in the wind tunnel at different wind speeds of (6 m/s, 8 m/s, and 10
m/s). We then calculate the mechanical torque of the turbine using a new and cheap
method in a short time to recode results data using the computer. Experimental results
showed an increasing performance efficiency and an increase in power coefficient by (18
%) of the new design compared to the classical turbine Savonius type elliptical.
Keywords: Savonius rotor; Blade shape; Coefficient of power.
Cite this Article: Salih Meri AR, Hamidon Bin Salleh B, Mohammed Najeh Nemah,
Balasem A. Al-Quraishi and Nor Zelawati Binti Asmuin, Performance Evaluation of
Savonius Wind Turbine Based on a New Design of Blade Shape, International Journal of
Mechanical Engineering and Technology, 10(01), 2019, pp.837–846
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837
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Salih Meri AR, Hamidon Bin Salleh B, Mohammed Najeh Nemah, Balasem A. Al-Quraishi and Nor
Zelawati Binti Asmuin
1. INTRODUCTION
Renewable energy like solar energy, biomass energy, marine energy (tides), wind energy and
geothermal energy is considered as the best and most suitable alternative way to produce cheap
electrical power. This clean energy is capable in enhancing the human’s life and make it more
easier [1]. Generally, using renewable energy leads to reduction in fully dependency of
consumption of traditional and fossil energy which causes environmental damage to humans,
animals and plants due to its thermal and gaseous emissions [2-4]. The exploitation of wind
energy is considered as one of the natural resources which are available nowadays to generate
cheap power. However, many researchers go complex and lengthy study to develop the
performance of the wind turbine system in order to obtain the best use of this energy [2], [5].
Among the problems and obstacles encountered in exploiting this source is the fluctuating wind
speed, fluctuations in urban conditions and the constant change in the direction of wind flow.
These problems have prompted many researchers interested in wind energy who tried to solve
these problems and studied how to improve the performance of wind turbines. One of the
solutions that contributed to the development of the wind power system is an innovative device
by engineer Savonius (1920) who obtained a patent and named the device after him [6]. The
Savonius wind turbine is a wind-powered device which consists of two half semi-circular parts
shaped like an English letter (S). The Savonius Wind Turbine is characterized based on the
features such as easy design, easy installation, low maintenance cost due to being close proximity
to the surface of the earth as well as possessing only few mechanical parts that attracts many
researchers to study and develop this device. The most important feature of the Savonius wind
turbine is self-start speed at low wind speeds [7-12]. The classical Savonius turbine is
characterized by its lower performance efficiency compared to most vertical axis wind turbines
VAWTs such as the Darrius , geometry parameters affecting the efficiency and the performance
of Savonius turbines such as blade shape, overlap ratio, the ratio height of rotor to diameter,
number of blades, addition of end plates, number of stages and other accessories [13-15]. Upon
focusing the wind flow towards the concave blade prevents the airflow from the convex side of
the blade using a number of wind guides. This idea contributed to increasing wind power,
reducing the negative torque and raising the maximum power coefficient by 0, 52 [16]. Dealing
with the parameter shape of the blade and its effective effect in increasing the performance of the
wind turbine, Savonius pulled most patrons on the study of the arc angle of the blade to raise the
coefficient of power. The angle of the arc at (120) provides the maximum energy coefficient of
the turbine [17]. Best curvature of the blade is obtained when the arc of the blade is equal to 70
[18]. The effect of two geometrical parameters are the angle of the arc of the blade and the overlap
ratio of the rotor part where the maximum power coefficient of up to (24.12%) is obtained
compared to the conventional turbine . A percentage increase in the coefficient of power about
(29%) at the arc angle of the blade (195) compared to the traditional blade with an angle (180) is
obtained [19]. A previous study was conducted to investigate the results of the experimental test
for wind turbine Savonius type elliptical by A. Sanusi [20]. The results were investigated at the
numerical test using the (CFD-Fluent) program with the same geometry parameters to improve
the blade shape [21]. The real torque of the Savonius wind turbine must be measured according
to the wind speed flowing on the rotor. There are several methods to measure and read the turbine
mechanical torque, for example, torque meter/ transducer (Torque sensor) is a Digital Torque
Meter with an external sensor to measure the static or startup torque moment in the shaft of the
turbine. It is connected directly to one end of the rotary shaft [22-24], unfortunately, its
disadvantage this method is that it has a high cost and is not available in the laboratory. The
method of weighing scale is a method in which the principle is based on the brake dynamometer
where poly is installed on the turbine shaft and wrapped around its rope tied by each end of the
digital weight scale. The torque is calculated as a result of mechanical load differentials due to
the friction force with the poly (braking force) when the wind turbine rotates [25], [26]. This
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Performance Evaluation of Savonius Wind Turbine Based on a New Design of Blade Shape,
method is easy to install and inexpensive, but among the disadvantages of this method is
inaccurate results and the time to measure the difference in loads is longest due to friction forces
oscillation between the rope and poly.
The main aim of this study is to design and experimentally evaluate a new wind turbine
Savonius. The new design has been designed by changing the shape of the blade with the overlap
ratio (0.2) based on the engineering parameters of the paper [20]. In addition, a new method of
measuring the output torque of the wind turbine is proposed by mean of using a DC generator
and a load control board. This method has a major advantage in recording the reading of the
experimental tests at relatively low cost and suitable time.
2. SAVONIUS WIND TURBINE PERFORMANCE
The most important output obtained from the work of the wind turbines Savonius is the
calculation of the maximum power coefficient and the maximum torque coefficient to determine
the effect of the geometric parameters on increasing and improving the performance of the wind
turbine. The calculated performance efficiency of the Savonius wind turbine by mathematical
relationship is the power coefficient ( ) and the torque coefficient ( ). The mathematical
relation of the power extracted as a result of a numerical or experimental test on the total
theoretical power expected from the airflow towards the turbine represents the power coefficient
as shown in the equations given below:
Output (Power turbine)
Input ( Power available)
C =
!
(1)
1
= # $ %&
2
(2)
Where ρ is the air density (kg/m3), A is the swept area of the turbine = 0.04 m2, while U is
the wind speed (m/s).
)*+ ,!
=
2-./
= / 2 34 = 5 ∗ 7
60
(3)
Here, T is the rotational torque, N is the revolution per minute (rpm), ω is the rotating speed
of the rotor (rad/s), V is voltage output of DC generator (Volt), and I is the current output of DC
generator (Amp).
The mathematical relation of the real torque extracted as a result of a numerical or
experimental test on the total theoretical torque expected from the airflow towards the turbine
represents the torque coefficient as shown in the equationsgiven below :
=
9:;<:; (/34=:> ;:4?@A>)
7A<:; ( /34=:> BCB@DB?D>)
=
(4)
/
(5)
1
# $F % G
2
/IF (J) =
2F
%
(6)
Where λ is the tip speed ratio.
=
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/2
1
&
2 #$%
839
=
/
2F
=
1
G %
#
$F
%
2
J
(7)
editor@iaeme.com
Salih Meri AR, Hamidon Bin Salleh B, Mohammed Najeh Nemah, Balasem A. Al-Quraishi and Nor
Zelawati Binti Asmuin
3. DESIGN DESCRIPTION AND METHODOLOGY
Savonius wind turbines are designed by using the program (CAD) depending on the optimal
engineering parameters as shown in figure (a) 1. In order to increase the pressure and positive
torque on the side of the blade concave, the new rotor blade is modelled by changing the inner
surface of the blade into a wavy shape.
The overlap ratio of the rotor is the effective geometry parameter in the performance
improvement, and the overlap ratio used in this model is equal to (0.2) with the rotor height ratio
to the diameter (1). In addition, the rotor diameter and the blade thickness are (200 mm, 4 mm),
respectively, with the addition of the end plats to up and down of the rotor, the optimum
measurement of end plate is (1.1D) times the rotor diameter [27].
b
a
Figure 1 Model of a new design Savonius elliptical rotor: a) Solid work model
b) The model printed by the 3D printer
Table 1 Description of geometric parameters
Geometric parameter
Value
Geometric parameter
Rotor diameter D
200 mm
Wind speed U
220 mm
Aspect ratio H/D
1
200 mm
0.2
No. of Stage
No. of Blade
1
2
End plate diameter 1.1
D
Height of the blade H
Overlap ratio (δ = e/d)
Blade chord length
e
d = 0.1 +
2
Value
6 m/s, 8 m/s,
10 m/s
112.5 mm
The Savonius rotor was manufactured using three-dimensional printing technology with a 3dimensional printer at the Universiti Tun Hussein Onn Malaysia (UTHM). The material
Acrylonitrile Butadiene Styrene (ABS) used is part of the thermoplastic polymers family
available in the market which is low cost taking into account the cost of manufacturing as shown
in figure (b) 1.
3.1. Wind tunnel setup
Laboratory experiments were carried out in the open-system wind tunnel at the Aerodynamic
Laboratory at the Universiti Tun Hussein Onn Malaysia (UTHM) as shown in Figure (2) and (3).
The wind speed in the wind tunnel ranges from (0 m/s to 39 m/s). In the wind tunnel system, a
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Performance Evaluation of Savonius Wind Turbine Based on a New Design of Blade Shape,
three-phase induction motor is used to control the speed of the frequency control device to reach
the desired wind speed. Measuring wind tunnel dimensions are about length of 600 cm and width
of 120 cm. The test section is rectangular shape at the size of length-120 cm, width-40 cm and
height-40 cm with a tight seal to keep it from leakage losses. The Savonius wind turbine is placed
at the center of the test section. The wind speed used in these tests is 6 m/s, 8 m/s and 10 m/s
measured using an Airflow meter with an accuracy of ±2.5% of reading at 10.00 m/s.
Figure 2 Test section in wind tunnel with Savonius wind turbine and electric control system
Figure 3 Schematic diagram of the wind tunnel with Savonius wind turbine and load control board
Figure 3 shows the proposed electronic load control board used in the experimental test. The
main purpose is to calculate the output torque of the Savonius wind turbine. The board consists
of 16 groups of small circular LEDs light with 12 mm diameter. Each group figures out from two
LEDs light controllable by a small electrical switch, while extra two switches are added to supply
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Salih Meri AR, Hamidon Bin Salleh B, Mohammed Najeh Nemah, Balasem A. Al-Quraishi and Nor
Zelawati Binti Asmuin
power to external loads, if necessary. The loads are connected in parallel with the DC generator
motor of the wind turbine, in order to keep the same voltage across each effective load. The total
voltage across the DC generator and the current throughout from it is measured by mean of using
LED DC Volt/Amp Meter as shown in Figure 4.
On the other hand, a digital rotary encoder is fixed directly on the shaft of the wind turbine,
as shown in Figure 2, to measure the turbine's rotational speed. The LED DC Volt/Amp Meter
and a digital rotary encoder were interfaced with the computer by using the Arduino UNO
microcontroller.
During the experiment, the turbine starts rotating freely without load. Following from there,
the experimenter works on increasing the load gradually. At each increase, the experimenter
records the voltage, current, and the turbine's rotational speed. The experiment is repeated for
each wind speed, i.e. 6 m/s, 8 m/s, and 10 m/s.
Figure 4 The load control board and its connections.
4. RESULTS AND DISCUSSIONS
4.1. Mechanical torque
The new model is tested under different wind conditions to determine the power generated at
each increase of the electric load in the control panel where all the recorded data are used for the
generated power and the rotational velocity of the corresponding turbine for the purpose of
calculating the experimental torque generated by using equation (6). Experimental tests for three
different values of wind speeds were used to study the wind power behavior in the new model at
wind speed. Figure (5) shows the relationship between the generated experimental turbine and
the tip speed ratio (TSR) of the new model and the traditional wind turbine Savonius, which
contributed to the new Savonius turbine in raising the positive momentum due to the increase of
the pressure on the concave side of the concave.
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Performance Evaluation of Savonius Wind Turbine Based on a New Design of Blade Shape,
Figure 5 Mechanical torque obtained using experimental test.
4.2. Power Coefficient and Torque Coefficient
For the purpose of calculating the power coefficient and the torque coefficient, the data for
rotational torque with revolution per minute of the turbine (rotational speed) of the new model
experiments is used in the wind tunnel at each case of wind speed. For comparing the performance
efficiency of the new Savonius wind turbine, the torque coefficient and power coefficient are
plotted for each wind velocity which represents the vertical axis with the tip speed ratio (TSR) at
the horizontal axis with the classical elliptical wind turbine Savonius at the wind speed 6 m/s as
shown in Figure (6) and (7).
The maximum coefficient of the new model is about 0.29 at wind speed of 6 m/s, 8 m/s, 10
m/s, respectively. The new model contributed to the efficiency of the performance, where the
percentage of increase in the coefficient of power up to (20%) compared to the classical elliptical
Savonius wind turbine.
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Salih Meri AR, Hamidon Bin Salleh B, Mohammed Najeh Nemah, Balasem A. Al-Quraishi and Nor
Zelawati Binti Asmuin
Figure 6 Torque coefficients
obtained using experimental test
Figure 7 Power coefficients
obtained using experimental test
5. CONCLUSION
In this paper, the behavior of the new wind turbine Savonius is studied at different wind speeds
of 6 m/s, 8 m/s, and 10 m/s by experimental testing in an open wind tunnel. Due to lack of sensors
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Performance Evaluation of Savonius Wind Turbine Based on a New Design of Blade Shape,
to measure the mechanical torque in the laboratory and expensive price, a new way to calculate
the torque was used by using the electric DC generator by connecting it to the rotary shaft with
an electric control panel to calculate the power generated at each rotating speed of the rotor and
record the all data by the computer automatically in a short time for each case. The new Savonius
wind turbine increased the performance efficiency by increasing the torque and power coefficient.
The ratio of the increase in the power coefficient for the new design was obtained (18 %) with
tip speed ratio (0.72) compared to the classical elliptical Savonius rotor.
ACKNOWLEDGEMENT
The authors would like to express special thanks to the research team of Energy and Thermofluid
Engineering in Faculty of Mechanical and Manufacturing Engineering, University Tun Hussein
Onn Malaysia (UTHM) and Iraqi Cement State Company, Ministry of Industry and Minerals,
Baghdad, Iraq for their financial and moral support in accomplishing this work.
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Zelawati Binti Asmuin
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