3C Tecnología. Glosas de innovación aplicadas a la pyme. ISSN: 2254 – 4143 Edición Especial Special Issue Noviembre 2020
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DESIGN AND CONSTRUCTION OF SAVONIUS ROTOR
Mirsad Hyder Shah
Student, Technische Universitat Dortmund.
Dortmund, (Germany).
E-mail: Itsmirsadhyder@yahoo.com ORCID: https://orcid.org/0000-0003-2476-5887
Sameer Ali Alsibiani
MD. Yanbu University College,
Yanbu Industrial City, (Kingdom of Saudi Arabia).
E-mail: Alsibianis@rcyci.edu.sa ORCID: https://orcid.org/0000-0003-1918-5175
Recepción:
04/09/2020
Aceptación:
07/10/2020
Publicación:
13/11/2020
Citación sugerida Suggested citation
Hyder, M., y Ali, S. (2020). Design and construction of Savonius rotor. 3C Tecnología. Glosas de innovación
aplicadas a la pyme. Edición Especial, Noviembre 2020, 65-77. https://doi.org/10.17993/3ctecno.2020.
specialissue6.65-77
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ABSTRACT
Renewable energy sources have been researched for more than a century now. Wind energy;
which is often characterized as an unreliable source of energy, is not unreliable if placed at
places with smooth wind currents. Savonius rotor as Vertical Axis Wind Turbine (VAWT)
can be used as a standalone power generation device because of its low cost, low cut-in
speed and the fact that it can accept wind from any direction. S-Rotors when compared to
other types of rotors have a lower Power Coecient but factors like Overlap ratio, Aspect
Ratio, Number of Blades and Blade shapes can aect its eciency. This paper discusses
the Design and construction of a Savonius wind turbine by studying how the factors above
inuence the rotor’s performance. Finally, a Single-stage, Two blade conventional Savonius
rotor with an Overlap Ratio of 0.1 and Aspect Ratio of 3.3 has been constructed and
discussed below. Studies for choosing the best material have also been conducted and
PolyVinyl Chloride (PVC) has been selected to prepare the blades from. According to the
study conducted, the voltage output recorded at 5.4 m/s wind speed was 19.1 Volts.
KEYWORDS
Savonius Rotor, Wind Turbine, S-Rotor, HAWT, VAWT.
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1. INTRODUCTION
Wind turbines are classied into two categories: HAWT and VAWT. This classication
refers to the position of rotor axis relative to wind direction. The Savonius rotor is thus
used as vertical axis wind turbine like the other Darrieus rotor. S-Rotors or Savonius rotors
have been employed as VAWT widely in the previous decades. The main reasons for which
S- rotors are employed in residential areas are because they are self-starting, produce low
noise and can accept wind energy from any directions. S-Rotors are also employed at places
with low wind potential and where HAWTs cannot run. Since the C
p
(Power Coecient)
of an S-Rotor is poor in large wind turbines, design parameters are altered as to improve
the power coecient by reducing the size of the rotor itself (Al-Kayiem, Bhayo, & Assadi,
2016).
The S-rotor was invented by Finnish engineer S. J. Savonius in 1925. As discussed earlier,
S-Rotors are generally preferred over D-rotor because of low cut-in speeds and high torque,
but their C
p
is poor when compared with other wind turbines. In 1919, German physicist
Albert Betz put forth what is known as the Betz theory. According to him, the theoretical
maximum eciency for a wind turbine is 59.3%. This value is generally known as the Betz
limit for wind turbines (Al-Kayiem et al., 2016).
Because of their superiority over other wind turbines, S-Rotors have been used to harness
energy for various purposes; mainly power generation, to meet electricity demands (Al-
Kayiem et al., 2016).
2. RESEARCH DESIGN AND CONSTRUCTION
2.1. BLADES SHAFT AND COUPLING OF WIND TURBINE
For the design of blades and the selection of material for the wind turbine, following factors
were taken into consideration:
• The blades of the windmill should not break if winds with high current cross the
surface.
• The material should not decompose over time and not prone to rusting in harsh
environment.
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• The material should be easily accessible.
• The cost of the material should be low cost.
• The blades should be durable in the long run.
Considering all the reasons mentioned above, Polyvinyl Chloride (PVC) was the best choice
available. After cutting the PVC to achieve the desired design the edges were smoothened
with sandpaper.
Table 1. Parameters and Values of Blades Shaft and Coupling.
PARAMETERS VALUES
Diameter of turbine 0.375 m
Volume of Blade 0.0395 m
3
Diameter of Single Blade 0.203 m
Overlap distance 0.0381 m
Density of PVC 1467 kg/m
3
Mass of PVC 3.8 kg
Blade angle 180º
Shaft Height 1.34 m
Shaft Diameter 0.036 m
Coupling Height 0.058 m
Bush size 0.02 m
The blades were weld to a shaft at an angle of 90 degrees, this enabled the blades to be
rotated by wind currents. The shaft had to be strong enough to withstand strong gushes of
wind and considering the work of Menet (2004); the shaft was made out of PVC.
Figure 1. AutoCAD vs Hardware of Blades and Shaft.
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2.2. BASE OF WIND TURBINE
For the construction of the base, mild steel bars were welded together to provide stability
to the whole design. For maximum stability a four legged stand base was proposed and
implemented.
Table 2. Parameters and values of base height and diameter.
PARAMETERS VALUES
Base Height 0.36 m
Base Diameter 0.56 m
Figure 2. AutoCAD vs Hardware of Base of Turbine.
3. IMPORTANT DESIGN PARAMETERS OF SAVNOIUS ROTORS
• Overlap Ratio.
• Aspect Ratio.
• Number of Blades.
• Number of Stages.
• Blade Shapes.
3.1. OVERLAP RATIO
The overlap ratio is ratio of the overlap distance (the distance by which the inner edge
of the blade overlaps the inner edge of the adjacent blade) by the diameter of the entire
turbine. As shown below in gure (Al-Kayiem et al., 2016).
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Figure 3. S-Rotor with Overlap ratio. Source: (Al-Kayiem et al., 2016).
3.2. ASPECT RATIO
Aspect Ratio is the ratio of Rotor’s height H to its Diameter D;
Increasing Aspect ratio increases performance and angular speed of the rotor. Aspect ratio
is adjusted to meet the torque and RPM requirements of the generator, which will produce
electricity (Al-Kayiem et al., 2016).
Blackwell, Sheldahl, and Feltz (1978), experimentally concluded that increasing aspect ratio
increased the power coecient (while keeping all other parameters constant).
3.3. NUMBER OF BLADES
With an increase in the number of blades the power coecient decreases. This decrease is
due to the fact that, as the number of blades is increased, more wind is deected by a blade
from entering into the concave side of its adjacent blades (Al-Kayiem et al., 2016).
Al-Kayiem et al. (2016) in his work concluded that S-Rotors indeed do perform better at
low wind currents. It is also compared and concluded that two blades perform better than
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three blades as more drag is wasted in the three-blade system. The C
p
of two blade design
is much better than a three-blade system.
Figure 4. S-Rotor with various number of blades. Source: (Al-Kayiem et al., 2016)
3.4. NUMBER OF STAGES
Number of stages mean one or more stages of an S-Rotor in a single design. This means
that the wind currents will have more area to sweep through and better torque uniformity
around 360 degrees. This eliminates the dead zones left by rotor’s blades that are not
rotating. Note that the stages of an S-Rotor are shifted at a specic phase shift angle.
In his paper, Al-Kayiem et al. (2016), debated that a Double staged S-Rotor may produce
the best power coecient as compared to a single or three staged S-Rotor. This explains the
hypothesis that as the stages of an S-Rotor are increased it means if one of the stages of
S-Rotor is rotating it must carry the inertia of the other stages since they are not producing
any torque.
Saha, Thotla, and Maity (2008), in his experimental work, concluded that a single staged
rotor gave a C
p
of 0.18, a two-staged rotor gave a power coecient of 0.29, while the three-
staged demonstrated a C
p
of only 0.23.
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Figure 5. Single and Multistage S-rotors. Source: (Al-Kayiem et al., 2016).
3.5. BLADE SHAPES
Although S-Rotors are generally similar S-shaped rotors, there have been few attempts to
modify the blade shape in order to increase its aerodynamic property in order to increase
the C
p
.
Muscoloa and Molnob (2014) simulated ve dierent S-type VAWTs, including a simple
S-Roto. In the four wind rotors, two were new models and two were proposed by Kyozuka
(2008). The rotor named Bronzinus, performed the best and produced the highest power
coecient. But if the tip speed was crossed C
p
of the wind rotor proposed by Menet (2004)
was found to be superior.
4. FINAL DESIGN OF ROTOR AND ASSEMBLY
The Rotor assembly consisted of the following parts:
• Base:
The base was made up of mild steel. The purpose of the base was to hold the rotor in its
place and provide a suitable height above the ground for the blades to face the wind. The
PMDC motor was coupled under the base as well. To provide maximum strength Mild steel
bars were welded in an L-shaped arrangement.
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• Bearing & Bearing Housing:
The purpose of the bearing was to support the shaft and lessen the friction for the shaft
to rotate. The bearing housing protects the bearing from any damage and restricts the
movement of the shaft.
• Motor Housing:
Motor housing consists of two horizontal plates made of Mild Steel which will have the
motor sandwiched in the between. The top end of the motor was secured to the assembly
by screws.
• Rotor Shaft:
The rotor shaft was made up of PVC. Due to its high strength, Polyvinyl Chloride was
chosen to withstand bending forces exerted by the rotating blades. The shaft had to be
strong enough to withstand strong gushes of wind and considering the work of Menet
(2004); the shaft was made out of PVC.
5. RESULTS
The parameters and values for the nal design have been presented in Table 3. As the
factors discussed above have been carefully considered such that the power coecient of
the rotor never drops. According to Al-Kayiem et al. (2016), the average Power Coecient
of an S-rotors under open ow conditions ranges from 0.037 to 0.37. However, the Power
Coecient of S-rotors with external ow guides can reach up to 0.52.
Table 3. Parameters and values of Final Design.
PARAMETERS VALUES
Model type Two blade conventional Savonius rotor
Height 1.25 m
Diameter 0.375 m
Area 0.456 m
2
Aspect ratio 3.3
Overlap ratio 0.1
Number of stages 1
Number of Blades 2
Design of Blade Conventional Blade
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In the Figure 6, the AutoCAD drawing and the actual hardware are shown. As the Savonius
rotor has a conventional blade design and it is a two blade system. Furthermore, it uses
minimal area and takes only 0.456 m² of area. The factors aecting the power coecient
of the S-rotor have also been calculated and presented.
Figure 6. AutoCAD vs Hardware of S-rotor.
In Table 4, the results for the wind turbine have been shown. The velocity of the wind was
measured using an anemometer which was placed right in front of the rotor. The wind
made the rotor move as intended. However, the maximum wind velocity that could be
simulated was 5.4 m/s. On the Beaufort Scale, such a wind speed has a Beaufort number
of 3 and is considered as a Gentle Breeze only. But due to the rotor being lightweight it was
easily rotated, and enough Revolutions were generated. At a windspeed of 5.4 m/s, the
generator under the S-Rotor generated 19.1 Volts.
Table 4. Results of Wind Turbine.
WIND SPEED m/s
RPM
VOLTAGES
4.1
200
14.91V
4.5
241
17.0V
4.9
253
18.17V
5.1
265
18.64V
5.4
302
19.1V
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6. CONCLUSION
This paper presented a study in which S-rotors have been employed as a power generation
unit. The design and construction of a Savonius rotor has been carried out in this paper
and S-rotors have been proved to be used in power generation units. S-Rotors are generally
highly aected by varying geometric parameters and blade shapes. S-rotors produce high
starting torques and low cut-in speeds. Furthermore, factors such as Overlap Ratio, Aspect
ratio, number of blades and number of stages have been briey discussed in this paper.
It is also concluded that by increasing/decreasing the factors discussed above, the Power
Coecient of the wind turbine varies. For the design of blades and the selection of material
for the wind turbine, Poly Vinyl Chloride (PVC) was chosen as the best material available. It
was chosen mainly because of its low cost and durability. Furthermore, choosing the suitable
Aspect and Overlap ratio is a dicult task but from the work of Blackwell et al. (1978) it can
be inferred that keeping the Overlap ratio to a minimal and increasing the Overlap ratio;
increased the power coecient of the Savonius Rotor. Finally, for a better power coecient,
the authors predict a two blade two stage rotor will do a better job for conventional wind
turbines but will prove ineective if the wind currents are equally distributed from the top
to the bottom on the whole blade design.
REFERENCES
Al-Kayiem, H. H., Bhayo, B. A., & Assadi, M. (2016). Comparative critique on
the design parameters and their eect on the performance of S-rotors. Renewable
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Blackwell, B. F., Sheldahl, R. E., & Feltz, L. V. (1978). Wind tunnel performance data
for two-and three-bucket Savonius rotors. Journal of Energy, 2(3), 160-164. https://
pdfs.semanticscholar.org/9c43/b66648d4396dc6a42cb27eb9f6a6563c21.pdf
Kyozuka, Y. (2008). An experimental study on the Darrieus-Savonius turbine for the
tidal current power generation. Journal of Fluid Science and Technology, 3(3), 439-449.
https://doi.org/10.1299/jfst.3.439
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