Published at : 24 Dec 2024
Volume : IJtech
Vol 15, No 6 (2024)
DOI : https://doi.org/10.14716/ijtech.v15i6.6110
Ivan Farozan | Faculty of Mechanical and Aerospace Engineering, Institut Teknologi Bandung, Bandung 40132, Indonesia |
Yuli Setyo Indartono | 1. Faculty of Mechanical and Aerospace Engineering, Institut Teknologi Bandung, Bandung 40132, Indonesia. 2. Research Center for New and Renewable Energy, Institut Teknologi Bandung, Bandung 40132, I |
The Savonius wind turbine is perceived favorable for a small-scale application because it is simple, relatively inexpensive, insensitive to wind directions, and has a good self-starting ability. However, it has a low power coefficient caused by the negative torque from the returning blade. This study aimed to investigate the effect of valve addition on the semi-circular Savonius rotor's performance. The experiments for this study were conducted on an open jet wind tunnel, with the valve located near the rotation axis, blade center, and rotor tip. The valve opening area ratio used was 0.02, 0.04, and 0.06, with Reynolds numbers 73,000, 86,000, and 99,000. The results showed that rotors with a valve placed near the tip performed better than those at the blade center and near the rotation axis. The performance decreased with an increase in the valve opening area ratio. Furthermore, the performance-improvement magnitude decreased with an increase in the Reynolds number. The rotor with a single valve near the tip performed the highest at a Reynolds number of 73,000. It achieved a maximum power coefficient of 0.199 compared to 0.183 obtained by a conventional Savonius rotor.
Augmentation; Check valve; Renewable energy; Savonius wind-rotor; Wind turbine
The Intergovernmental Panel on
Climate Change (IPCC) warned that the world would reach 1.5 oC of
warming by 2040, and only swift and drastic cuts in carbon emissions would help
prevent an environmental disaster (IPCC, 2022). One way to reduce carbon emissions is reduced by
using renewable energy sources such as wind energy to decarbonize the global
electricity generation systems. In 2019, global wind power capacity reached 651
GW, contributing approximately 5.9% of global electricity generation (REN21, 2019). With wind energy
costs expected to drop significantly in the future, this contribution is
expected to increase (Wiser et al., 2021).
Savonius rotor is a vertical axis wind turbine (VAWT) comprising two semi-circular buckets arranged asymmetrically to resemble an 'S' shape. It works based on drag force with a slight contribution from the lift force (Alom, Borah, and Saha, 2018). The positive torque generated by an advancing blade moving with the wind is higher than the negative torque generated by the returning blade moving against the wind. The difference between the two torques causes the rotor to spin. The Savonius rotor power coefficient (CP) is much lower than the horizontal axis wind turbine (HAWT) due to the negative torque produced. However, it has several intrinsic advantages over the HAWT, such as simpler design, good starting ability, omnidirectional, lower noise, and easier to maintain (Kumar, Raahemifar, and Fung, 2018). These advantages make the rotor more suitable for harnessing wind power in urban sites, building rooftops, and remote areas (Cho, Jeong, and Sari, 2011; Ishugah et al., 2014; Mao et al., 2020). In addition to energy generation, wind turbines installed in an urban area allow direct use of energy which eliminates energy transmission losses (Krasniqi, Dimitrieska, and Lajqi, 2022). When combined with a suitable and improved generator design, such as a reduced cogging-torque permanent magnet generator (Nur and Siregar, 2020), the Savonius rotor may provide an interesting method for small-scale wind power generation. The basic geometry of a conventional Savonius rotor is illustrated in Figure 1.
Figure 1 Basic
geometry of a conventional Savonius rotor
The performance of a Savonius
rotor highly depends on its geometric parameters. Saad et
al. (2020) found that the rotor
with end plates performed better, with the optimum value for end plate diameter
(De) at 1.1 of the rotor diameter (D). Mahmoud
et al. (2012) investigated
the aspect ratio (AR), a non-dimensional parameter resulting from dividing the
rotor height (H) by its diameter. The study found that the maximum CP
(CPMax) was improved as the AR increased. Saad, Ookawara,
and Ahmed (2022) observed a similar finding on multi-stage rotors. This
CP improvement for a higher AR reduces loss at the tip, similar to
adding end plates (Akwa, Vielmo, and Petry, 2012). Studies on the overlap ratio (?) of the distance
between rotor blades (e) and the blade chord length (d) found that the optimum
value ranges from 0.15 to 0.2 (Alom and Saha, 2017;
Cuevas-Carvajal et al., 2022; Roy and Saha, 2013). Additionally, Kamoji,
Kedare, and Prabhu (2009) investigated the effect of the Reynolds number on a
conventional and modified Savonius rotor. The study found that the CPMax
improved by 19% as the Reynolds number increased from 80,000 to 150,000.
The modification f the
conventional Savonius rotor blade shape can also improve its performance. Abdelaziz et al. (2022) numerically
studied the performance of a conventional Savonius rotor with various outer and
inner arc angles and gap ratios. They managed to improve the CPMax
by 4.5% and 12.9% with a 160O outer angle and 20O inner
angle, respectively. A novel Savonius rotor with a modified-bach blade was
proposed by Elmekawy, Saeed, and Kassab (2021). They found a 32.2% CPMax improvement over
a conventional Savonius rotor through numerical study. The blade shape was also
modified to improve the Savonius performance at a higher TSR range (above 0.8).
Savonius rotor with a combination of the semi-circular and elliptical profile
was found to have CPMax at TSR=1.4, double that of a conventional
rotor's TSR=0.7 (Le et al., 2022). Based on the result, Dinh
Le, Minh, and Trinh (2022) further
modified the previous rotor into a combination of multi-curve and auxiliary
blades. The new rotor combination not only possessed a higher CPMax
at a higher TSR, but it also exhibited a 6.9% higher CP than the
conventional rotor in the lower TSR range.
Several studies have suggested
different methods to enhance the performance of the Savonius rotor. For
instance, Mohamed et al. (2010) improved the CP by 27.3% by placing a deflector upstream to prevent the
wind from hitting the returning blade. Nimvari,
Fatahian, and Fatahian (2020) used a porous deflector and achieved a 10% increase
in CPMax. El-Askary et al.
(2015) proposed a design that
incorporated a Savonius rotor inside curved guide plates, which achieved a CPMax
of 0.52 at a TSR of 1.1. However, this design produced large wakes behind
the rotor, which could affect the operation of other turbines in a wind farm.
Although these methods significantly improve performance, they compromise the
simplicity and omnidirectional nature of the Savonius rotor.
Ideal augmentation methods can
improve rotor performance while keeping all the Savonius advantages intact. One
of the methods is the addition of a check valve to the rotor blades. This
method allows a portion of wind freestream to pass through the returning-blade
convex side, reducing the drag force and lowering the negative torque.
Furthermore, valve addition can be a complementary method with the potential to
further enhance an already high-performance Savonius rotor with a modified
blade.
Rajkumar and Saha (2006) first investigated the valve-addition method by placing slot-shaped
aluminum hinged-type valves on a conventional and twisted Savonius rotor. Saha Thotla, and Maity (2008) later used a thin fabric called Rexine as the valve
material instead of aluminum and conducted experiments using an open jet wind
tunnel. The findings showed that the two-stage, valve-aided Savonius rotor had
a 19% higher CPMax than a conventional rotor. Both of the
aforementioned studies used a fixed-size valve placed at the center of the
blade. Amiri and Anbarsooz (2019) investigated the effect of valve location on a conventional Savonius
rotor's performance. The study used a rectangular pivot-type valve made from
the same material as the rotor. The valve's opening area ratio (OAR), which is
the ratio between the area of the valves and the rotor's frontal area (D.H),
was fixed at 0.33. This pivotal valve was placed near the rotation axis as well
as in the middle and at the tip of the rotor. The results showed that the valve
at the tip location yielded a 20.8% performance improvement. Furthermore, Borzuei, Moosavian, and Farajollahi (2021) performed a numerical experiment on the effect of
adding a rectangular pivot-type valve to the static torque coefficient of a
Savonius rotor with three blades. The results showed a 14.5% improvement in the
static torque coefficient. This was indicated by the large pivot valve with an
unlimited opening angle and counter-clockwise opening direction placed at the
center of the rotor blade.
Previous studies have shown that using a part of the rotor blade as a pivot-type valve can have a positive effect (Borzuei, Moosavian, and Farajollahi, 2021; Amiri and Anbarsooz, 2019). However, a large OAR can have a negative impact on the structural integrity and manufacturability of the rotor. The slot-shaped hinge-type valve proposed by Saha, Thotla, and Maity (2008) has better structural integrity and manufacturability. However, previous studies on Savonius rotors with hinge-type valves did not investigate the effect of valve locations and OAR on the rotor's performance under different wind speeds. This study aims to fill this gap. Moreover, in contrast to the slot-shaped valve used in by Saha, Thotla, and Maity (2008) this study employs a circular valve to improve the manufacturability of the rotor blade.
2.1.
Studied Rotor Design and
Manufacturing
This study investigated a
single-stage Savonius with two semi-circular rotor blades. All the studied
rotors have the same design and dimension. The valves were placed near the
rotor rotation axis (A), at the center of the rotor blade (B), and near the rotor
tip (C). Moreover, the study used three increasing OAR for each location to
study ten rotors, including the non-valve-aided rotor. Tables 1 and 2 show the
geometrical dimension and rotor specifications, while the valve location and
arrangements are depicted in Figure 2a.
The rotors were manufactured using 3D printers and
PLA+ material with a thickness of 2.5mm. Each rotor was divided into lower and
top plates and rotor blades, a design chosen to reduce manufacturing time and
material use while allowing for quick reconfiguration. The valve body was made
from synthetic leather pasted onto the rotor blade. Figure 2b shows the
manufactured rotors.
Table 1 Geometrical
dimension of the studied Savonius semi-circular rotor
Chord length (d) |
Rotor diameter (D) |
End plate diameter (De) |
Rotor Height (H) |
Rotor Aspect ratio (AR) |
Overlap ratio (?) |
100 mm |
180 mm |
198 mm |
360 mm |
2 |
0.2 |
Table 2 Studied
rotors identification and specification
Parameter |
Rotor Identification | ||||||||||
SCNV |
SCA1 |
SCA2 |
SCA3 |
SCB1 |
SCB2 |
SCB3 |
SCC1 |
SCC2 |
SCC3 |
| |
Valve Location |
N/A |
Near the rotation axis |
At the blade center |
Near rotor tip | |||||||
Valve Qty |
0 |
1 |
2 |
3 |
1 |
2 |
3 |
1 |
2 |
3 |
|
OAR |
0 |
0.02 |
0.04 |
0.06 |
0.02 |
0.04 |
0.06 |
0.02 |
0.04 |
0.06 |
|
Figure 2 (a) Valve locations and arrangement on the rotor; (b)
3D printed rotors
2.2.
Experimental Setup
The experiments were performed
using the low-speed open jet wind tunnel at the Institut Teknologi Bandung. The
wind velocity at the tunnel exit () could be adjusted up to
10 m/s using a variable speed drive. The averaged wind velocity at the tunnel
exit was measured using a calibrated hotwire anemometer. The experiments were
conducted at a Reynolds number of 73,000, 86,000, and 99,000. The rotor axis was positioned 300 mm away from the
wind tunnel exit. The open test section in which the rotor was situated
measured 1,000 mm x 600 mm, resulting in a blockage ratio of 12%. This value is
low for an open-type wind tunnel test and does not require a blockage
correction factor (Gonçalves, Pereira, and Sousa, 2022; Van Bussel et al., 2004). The overall setup of the experimental study is
depicted in Figure 3a.
The study used a DYN-200 rotary torque
meter to measure the torque (T) and the rotor's rotation speed (N).
The torque meters measurement was calibrated using known torques, while the
rotation speed was checked against a calibrated optical tachometer. The meter
accuracy was specified as ±0.1% and ±1 rpm for the torque and rotation speed,
respectively. Furthermore, the torque meter output was connected to a laptop
via a Labjack U6 data acquisition module. A hysteresis brake and a DC generator
were combined to simulate a dynamic load. At each test point, measurements were
taken at a sampling rate of 4 Hz for 15
seconds. Figure 3b shows the instrumental setup.
Figure 3 (a) Overall experimental setup; (b) Instrumentation
setup
2.3.
Data Reduction
The study measured the freestream wind velocity
(), rotor torque (T), and rotor rotational
speed (N). The rotor was operated under a steady wind velocity and
constant load during a dynamic test. The torque and rotation speeds were
measured for a fixed time and then averaged. The load was then varied to obtain
the rotor's performance characteristics. The torque loss due to bearing
frictions cannot be ignored at higher rotational speeds. Therefore, a separate
experiment was conducted to obtain the frictional power loss characteristic.
The dimensionless rotor tip speed ratio (TSR) was then calculated using
Equation 1:
where D is the rotor diameter (m), is the
wind velocity (m/s), and is the
rotor angular velocity (rad/s) calculated using Equation 2:
where N is the measured rotor rotation speed (rpm). The dimensionless rotor power coefficient CP is expressed using Equation 3:
where TSR is the tip speed ratio given by
Equation 1, and is the
dimensionless rotor torque coefficient calculated using Equation 4:
where T is the measured torque (N.m), H is the rotor height (m), and is the air density in (kg/m3).
The uncertainty related to the
measurement is calculated using the root-sum-square method (Wheeler and Ganji, 2009). The
total uncertainties for the measured quantities (T, N, and ) are
calculated using Equation 5:
where is the systematic uncertainty taken from the
instrument's accuracy specification, and is the random uncertainty based on the standard
deviation of the mean. The uncertainties for derived quantities are then calculated using the propagation of
error method shown in Equation 6:
where is the total uncertainty for the derived
quantities, and is the sensitivity coefficient of derived
quantities R with respect to variable The confidence level associated with the
uncertainties was chosen at 95%. The total uncertainties for the TSR, are 2.3%,
4.0%, and 6.3% respectively.
3.1.
Conventional (Non-Valve-Aided) Savonius
Rotor Performance
Figure 4 The effect of Reynolds number on the Savonius rotor
(a) coefficient of power; and (b) coefficient of torque
The results suggest that the power
coefficient increased as the Reynolds number increased. The CPMax
value increased by 14.6% as the Reynolds number increased from 73,000 to
99,000, which is consistent with the findings of Kamoji,
Kedare, and Prabhu (2009). The increase in CPMax
was attributed to the delayed separations at the rotor blades at higher
Reynolds numbers or wind velocities (Kamoji, Kedare, and Prabhu, 2009). Similarly, the CTMax also increased
with the Reynolds number. The CTMax values for Reynolds numbers
73,000, 86,000, and 99,000 were 0.284, 0.304, and 0.323, respectively. The CT
peaked at a tip speed ratio of 0.4 and decreased almost linearly as the tip
speed ratio increased, which was observed for all three Reynolds numbers.
3.2.
Effect of Valve Locations on the Rotor
Performance
Figure 5 The effect of valve locations on SCNV, SCA1, SCB1, and SCC1 rotor (a) CP vs TSR at Re=73,000; (b) CP vs TSR at Re=86,000; (c) CP vs TSR at Re=99,000; (d) CT vs TSR at Re=73,000; (e) CT vs TSR at Re=86,000; and (f) CT vs TSR at Re=99,000
The
rotors with a single valve performed better than the non-valve-aided (SCNV)
rotors in all three locations and for all Reynolds numbers. However, the
magnitude of CPMax improvement decreased as the Reynolds number
increased. For instance, the SCC1 rotor yielded an 8.7%, 7.0%, and 5.2% CPMax
improvement when tested at Reynolds numbers 73,000, 86,000, and 99,000,
respectively. This condition may be caused by the valve's presence on the blade
surface disrupting the flow-separation delay that normally occurs when the
Reynolds number increases. Adding a single valve did not significantly affect
the tip speed ratio corresponding with the CPMax. The tip speed
ratio range related to the CPMax is 0.85 to 0.87 compared to SCNVs
0.84 to 0.86. A similar observation was made by Amiri and Anbarsooz (2019).
The
rotor with a valve near the rotor tip (SCC1) consistently showed higher CPMax
than the other two for the three Reynolds numbers. This result is consistent
with Amiri and Anbarsooz (2019) that the negative torque
reduction by the valve at the tip has a greater impact because the air flows
through the valve at a higher rate. In contrast, the rotor with a valve placed
near the rotation axis (SCA1) produced the least improvement. A valve at this
location is too close to the moment axis, resulting in the lowest negative
torque reduction. Placing a valve near the rotation axis also disturbs the
overlapping-gap flow that is supposed to energize the returning blade (Nakajima, Iio, and Ikeda, 2008). The overlapping-gap flow
disturbance further reduces the effectiveness of the valve placed near the
rotation axis. This finding shows a tradeoff between the positive and negative
effects on each valve location.
Adding
a single valve to the rotor did not change the trend of rotor CT.
Similar to the non-valve-aided rotor (SCNV), the CTMax occurred at
TSR=0.4 and decreased as the TSR increased. This applied to all three
valve-aided rotors (SCA1, SCB1, and SCC1). The value of the CTMax
for SCC1 and SCB1 rotors increased, while the SCA1 rotor CTMax
remained close to the SCNV. Similar to the CP result, the magnitude
of CTMax improvement decreased as the Reynolds number increased. A
comparison of the result between the present study and the works of Amiri and Anbarsooz (2019) and Saha, Thotla,
and Maity (2008) can be found in Table 3.
Table 3 Result comparison
for studies on Savonius rotor aided with a single valve
Author |
Valve shape |
Valve location |
Valve OAR |
Reynolds Number |
CPMax |
TSR for CTMax |
Saha, Thotla, and Maity (2008) |
Slot |
Center |
Not specified |
148,000 (estimated) |
0.310 |
Not specified |
Amiri and Anbarsooz (2019) |
Rectangular |
Center |
0.33 |
138,000 (estimated) |
0.116 |
0.55 |
The present study |
Circular |
Center |
0.02 |
73,000 |
0.199 |
0.87 |
3.3.
Effect of Valve Opening Area Ratio on the
Rotor Performance
The
valve opening area ratio was varied between 0.02 and 0.06 by increasing the
number of valves with the same diameter. A total of six multi-valve rotors
(SCA2, SCA3, SCB2, SCB3, SCC2, and SCC3) were made and tested in this study.
The results showed a similar trend for the three-valve locations. Therefore,
the study discussed the results mainly from SCC1, SCC2, and SCC3, with the
valve at the tip. Figures 6a and 6b illustrate the effect of OAR on the SCC
rotor CP and CT at the same Reynolds number of 73,000,
while Table 4 summarizes the overall experiment result.
Figures 6a and 6b show that the rotors' performance coefficient decreases as the valve OAR increases. The CPMax at Re=73,000 for SCC1, SCC2, and SCC3 is 0.199, 0192, and 0.187, respectively. The CTMax for SCC1, SCC2, and SCC3 is 0.302, 0.291, and 0.284, respectively. Table 4 shows that these CPMax and CTMax downward trends can be observed in all three valve locations and for all Reynolds numbers. This result indicates that the amplification of positive effects from increasing OAR, such as negative torque reduction, is weaker than that of negative effects. The design and working mechanism of the hinge-type valve may contribute to the reduced performance. The thin synthetic-leather fabric used as the valve material could be affected by the airflow condition and lifted open when unexpected.
Figure 6 The
effect of valve locations on SCNV, SCC1, SCC2, and SCC3 rotor (a) CP vs
TSR at Re=73,000; (b) CT vs TSR at Re=73,000
Figure
7 shows the opening of all valves at returning and advancing blade side for the
SCC3 rotor at 150O relative to the incoming wind. Opening the valves
at the advancing side reduces the blade surface pushed by the wind, lowering
the net torque value. This phenomenon is also observed with SCC1 and SCC2.
Furthermore, increasing the OAR (number of valves) near the rotation axis has
further disturbed the overlapping-gap flow, which cannot be compensated by the
negative torque reduction effect. Figure 8 shows the plot for valve-aided
rotors' CPmax improvement over the SCNV.
Figure 8 Summary of valve-aided rotors CPmax
improvement over the SCNV rotor
The study aimed to compare the performance of
conventional and valve-aided Savonius wind rotors with semi-circular blades by
varying valve locations, OAR, and Reynolds numbers. Results indicated that
rotor power and torque coefficient increased with Reynolds numbers. For all
Reynolds numbers and OAR values, rotors with valves at the rotor tip
outperformed those in other locations. Additionally, rotor performance
decreased as valve OAR increased due to coexisting adverse effects like flow
disruption alongside the beneficial effect of negative torque reduction. The
highest CPMax improvement of 8.7% was shown by the rotor with a
single valve at the tip, with a CPMax of 0.199 at a tip speed ratio
of 0.87. The augmentation of the Savonius rotor with valve addition improved
the rotor performance while keeping all the intrinsic advantages intact.
Therefore, a valve-assisted Savonius wind rotor can potentially enhance wind
power generation in urban areas and sites with a low average wind speed.
The authors
thank the Faculty of Mechanical and Aerospace Engineering (FTMD) ITB for their financial support
through the Penelitian, Pengabdian Masyarakat, dan Inovasi (P2MI) 2021~2022 grant
scheme. The authors
would also like to extend their gratitude to the Research Center for New and
Renewable Energy ITB for their support so that this study could be conducted.
Filename | Description |
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R1-ME-6110-20221203071122.png | Figure 1 |
R1-ME-6110-20221203071249.png | Figure 2a |
R1-ME-6110-20221203071327.JPG | Figure 2b |
R1-ME-6110-20221203071548.jpg | Figure 3a Revised |
R1-ME-6110-20221203071613.jpg | Figure 3b |
R1-ME-6110-20221203072609.png | Figure 4a |
R1-ME-6110-20221203072630.png | Figure 4b |
R1-ME-6110-20221203072652.jpg | Figure 5a revised |
R1-ME-6110-20221203072742.jpg | Figure 5b revised |
R1-ME-6110-20221203072816.jpg | Figure 5c revised |
R1-ME-6110-20221203072836.jpg | Figure 5d |
R1-ME-6110-20221203072855.jpg | Figure 5e |
R1-ME-6110-20221203072915.jpg | Figure 5f |
R1-ME-6110-20221203073018.jpg | Figure 6b |
R1-ME-6110-20221203073050.jpg | Figure 7 |
R1-ME-6110-20221203073125.JPG | Figure 8 |
R1-ME-6110-20221203073604.jpg | Figure 6a revised |
Abdelaziz, K.R., Nawar, M.A.A., Ramadan, A., Attai, Y.A., Mohamed, M.H.,
2022. Performance Investigation of a Savonius Rotor by Varying the Blade Arc
Angles. Ocean Engineering, Volume 260, p. 112054. https://doi.org/10.1016/j.oceaneng.2022.112054
Akwa, J.V., Vielmo, H.A., Petry, A.P., 2012. A Review on the Performance
of Savonius wind Turbines. Renewable and Sustainable Energy Reviews,
Volume 16(5), pp. 3054–3064. https://doi.org/10.1016/J.RSER.2012.02.056
Alom, N., Borah, B., Saha, U.K., 2018. An
Insight into the Drag and Lift Characteristics of Modified Bach and Benesh
Profiles of Savonius Rotor. Energy Procedia, Volume 144, pp. 50–56. https://doi.org/10.1016/j.egypro.2018.06.007
Alom, N., Saha, U.K., 2017. Arriving at the optimum overlap ratio for an
elliptical-bladed savonius rotor. Proceedings of the ASME Turbo Expo,
Volume 9, pp. 1–10. https://doi.org/10.1115/GT2017-64137
Amiri, M., Anbarsooz, M., 2019. Improving the Energy Conversion
Efficiency of a Savonius Rotor Using Automatic Valves. Journal of Solar
Energy Engineering, Volume 141(3), p. 031017. https://doi.org/10.1115/1.4042828
Banerjee, A., 2019. Performance and flow analysis of an elliptic bladed
Savonius-style wind turbine. Journal of Renewable and Sustainable Energy,
Volume 11(3), p. 033307. https://doi.org/10.1063/1.5097571
Borzuei, D., Moosavian, S.F., Farajollahi, M., 2021. On the Performance Enhancement of the Three-Blade
Savonius Wind Turbine Implementing Opening Valve. Journal of Energy
Resources Technology, Volume 143(5), p. 051301. https://doi.org/10.1115/1.4049460
Cho, K.-P., Jeong, S.-H., Sari, D.P., 2011. Harvesting Wind Energy from
Aerodynamic Design for Building Integrated Wind Turbines. International
Journal of Technology, Volume 2(3), pp. 189–198. https://doi.org/10.14716/ijtech.v2i3.65
Cuevas-Carvajal, N., Cortes-Ramirez, J.S., Norato, J.A., Hernandez, C.,
Montoya-Vallejo, M.F., 2022. Effect of Geometrical Parameters on the
Performance of Conventional Savonius VAWT: A Review. Renewable and
Sustainable Energy Reviews, Volume 161, p. 112314. https://doi.org/10.1016/J.RSER.2022.112314
Dinh Le, A., Minh, B.D., Trinh, C.D., 2022. High Efficiency Energy
Harvesting Using a Savonius Turbine with Multicurve and Auxiliary Blade. Journal
of Fluids Engineering, Volume 144(11), p. 111207. https://doi.org/10.1115/1.4054705
El-Askary, W.A., Nasef, M.H., AbdEL-hamid, A.A., Gad, H.E., 2015.
Harvesting Wind Energy for Improving Performance of Savonius Rotor. Journal
of Wind Engineering and Industrial Aerodynamics, Volume 139, pp. 8–15. https://doi.org/10.1016/j.jweia.2015.01.003
Elmekawy, A.M.N., Saeed, H.A.H., Kassab, S. Z., 2021. Performance
Enhancement of Savonius Wind Turbine by Blade Shape and Twisted Angle
Modifications. In: Proceedings of the Institution of Mechanical
Engineers, Part A: Journal of Power and Energy, Volume 235(6), pp. 1487–1500. https://doi.org/10.1177/0957650920987942
Ferrari, G., Federici, D., Schito, P., Inzoli, F., Mereu, R., 2017. CFD
study of Savonius wind turbine: 3D model validation and parametric analysis. Renewable
Energy, Volume 105, pp. 722–734. https://doi.org/10.1016/j.renene.2016.12.077
Gonçalves, A.N.C., Pereira, J.M.C., Sousa, J.M.M., 2022. Passive Control
of Dynamic Stall in a H-Darrieus Vertical Axis Wind Turbine using Blade
Leading-Edge Protuberances. Applied Energy, Volume 324, p. 119700. https://doi.org/10.1016/j.apenergy.2022.119700
Intergovernmental Panel on Climate Change (IPCC), 2022. Summary for
Policymakers. Report in Climate Change 2022: Impacts, Adaptation and
Vulnerability, Contribution of Working Group II to the Sixth Assessment Report
of the Intergovernmental Panel on Climate Change, IPCC, New York, USA. https://doi.org/10.1017/9781009325844.001
Ishugah, T.F., Li, Y., Wang, R.Z., Kiplagat, J.K., 2014. Advances in
Wind Energy Resource Exploitation in Urban Environment: A Review. Renewable
and Sustainable Energy Reviews, Volume 37, pp. 613–626. https://doi.org/10.1016/j.rser.2014.05.053
Kamoji, M.A., Kedare, S.B., Prabhu, S.V., 2009. Experimental
Investigations on Single Stage Modified Savonius Rotor. Applied Energy,
Volume 86(7–8), pp. 1064–1073. https://doi.org/10.1016/J.APENERGY.2008.09.019
Krasniqi, G., Dimitrieska, C., Lajqi, S., 2022. Wind Energy Potential in
Urban Area: Case Study Prishtina. International Journal of Technology,
Volume 13(3), pp. 458–472. https://doi.org/10.14716/ijtech.v13i3.5323
Kumar, R., Raahemifar, K., Fung, A.S., 2018. A Critical Review of
Vertical Axis Wind Turbines for Urban Applications. Renewable and
Sustainable Energy Reviews, Volume 89, pp. 281–291. https://doi.org/10.1016/j.rser.2018.03.033
Le, A.D., Minh Duc, B., van Hoang, T., The Tran, H., 2022. Modified
Savonius Wind Turbine for Wind Energy Harvesting in Urban Environments. Journal
of Fluids Engineering, Volume 144(8), p. 081501. https://doi.org/10.1115/1.4053619
Mahmoud, N.H., El-Haroun, A.A., Wahba, E., Nasef, M.H., 2012. An
Experimental Study on Improvement of Savonius Rotor Performance. Alexandria
Engineering Journal, Volume 51(1), pp. 19–25. https://doi.org/10.1016/J.AEJ.2012.07.003
Mao, Z., Yang, G., Zhang, T., Tian, W., 2020. Aerodynamic performance
analysis of a building-integrated Savonius turbine. Energies, Volume
13(10), p. 2636. https://doi.org/10.3390/en13102636
Mohamed, M.H., Janiga, G., Pap, E., Thèvenin, D., 2010. Optimization of
Savonius Turbines using an Obstacle Shielding the Returning Blade. Renewable
Energy, Volume 35(11), pp. 2618–2626. https://doi.org/10.1016/j.renene.2010.04.007
Nakajima, M., Iio, S., Ikeda, T., 2008. Performance of Double-step
Savonius Rotor for Environmentally Friendly Hydraulic Turbine. Journal of
Fluid Science and Technology, Volume 3(3), pp. 410–419. https://doi.org/10.1299/jfst.3.410
Nimvari, M.E., Fatahian, H., Fatahian, E., 2020. Performance Improvement
of a Savonius Vertical Axis Wind Turbine using a Porous Deflector. Energy
Conversion and Management, Volume 220, p. 113062. https://doi.org/10.1016/j.enconman.2020.113062
Nur, T., Siregar, M., 2020. Two-Steps Slotting Method in Magnet Edge of
PMG for Wind Energy Harvesting. International Journal of Technology, Volume
11(7), pp. 1442–1450. https://doi.org/10.14716/ijtech.v11i7.4554
Rajkumar, M.J., Saha, U.K., 2006. Valve-Aided
Twisted Savonius Rotor. Wind Engineering, Volume 30(3), pp. 243–254. https://doi.org/10.1260/030952406778606269
Renewable Energy Policy Network for the 21st Century (REN21), 2019. Renewables
2019 Global Status Report. Renewable
Energy Policy Network for the 21st Century, REN21 Secretariat, Paris, France
Roy, S., Saha, U.K., 2013. Computational
Study to Assess the Influence of Overlap Ratio on Static Torque Characteristics
of a Vertical Axis Wind Turbine. Procedia Engineering, Volume 51, pp.
694–702. https://doi.org/10.1016/J.PROENG.2013.01.099
Roy, S., Saha, U.K., 2015. Wind tunnel experiments of a newly developed
two-bladed Savonius-style wind turbine. Applied Energy, Volume 137, pp.
117–125. https://doi.org/10.1016/j.apenergy.2014.10.022
Saad, A.S., El-Sharkawy, I.I., Ookawara, S., Ahmed, M., 2020.
Performance Enhancement of Twisted-Bladed Savonius Vertical Axis Wind Turbines.
Energy Conversion and Management, Volume 209, p. 112673. https://doi.org/10.1016/j.enconman.2020.112673
Saad, A.S., Ookawara, S., Ahmed, M., 2022. Influence of Varying the
Stage Aspect Ratio on the Performance of Multi-Stage Savonius Wind Rotors.
Journal of Energy Resources Technology, Volume 144(1), p. 011301. https://doi.org/10.1115/1.4050876/1107060.
Saha, U.K., Thotla, S., Maity, D., 2008. Optimum Design Configuration of Savonius Rotor Through Wind Tunnel
Experiments. Journal of Wind Engineering and Industrial Aerodynamics, Volume
96(8–9), pp. 1359–1375. https://doi.org/10.1016/J.JWEIA.2008.03.005
Torresi, M., de Benedittis, F.A., Fortunato, B., Camporeale, S.M., 2014.
Performance and Flow Field Evaluation of a Savonius Rotor Tested in a Wind
Tunnel. Energy Procedia, Volume 45, pp. 207–216. https://doi.org/10.1016/J.EGYPRO.2014.01.023
Van Bussel, G.J.W., Mertens, S., Polinder, H., Sidler, H.F.A., 2004. The
Development of Turby, A Small Vawt for the Built Environment. In:
Proceedings of the Global Windpower 2004 Conference and Exhibition, pp. 1–10
Wheeler, A., Ganji, A., 2009. Introduction to Engineering
Experimentation. 3rd Edition. USA: Pearson
Wiser, R., Rand, J., Seel, J., Beiter, P., Baker, E., Lantz, E., Gilman,
P., 2021. Expert Elicitation Survey Predicts 37% to 49% Declines in Wind Energy
Costs by 2050. Nature Energy, Volume 6(5), pp. 555–565. https://doi.org/10.1038/s41560-021-00810-z