65
Indonesian Journal of Science & Technology 7.
65-88 Indonesian Journal of Science & Technology Journal homepage: http://ejournal.
edu/index.
php/ijost/ Aerodynamic Performance of Vertical and Horizontal Axis Wind Turbines: A Comparison Review Hesam Eftekhari.
Abdulkareem Sh.
Mahdi Al-Obaidi*.
Shahrooz Eftekhari School of Computer Science and Engineering.
Faculty of Innovation.
TaylorAos University.
No.
1 Jalan SS 15/8 47500 Subang Jaya.
Selangor DE.
Malaysia Correspondence: E-mail: abdulkareem.
mahdi@taylors.
ABSTRACT
ARTICLE INFO
The need for energy and electricity has been increasing globally, and this means more power is required from the power plants.
Power plants, however, will then continue harming the earth because of the greenhouse gasses produced while generating energies that contribute to global warming.
Using renewable sources to produce clean energies is one of the sustainable methods to deal with such challenges.
Wind energy is one of the renewable sources, which is accessible anywhere on earth, creating green energy.
Wind turbines are mainly categorized into Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT).
This paper firstly presents a general comparison between the HAWTs and VAWTs.
Then, it presents mathematical modelling for the aerodynamic factors of HAWT and Darrieus VAWT to assist the researchers to understand some key design aspects of wind turbines, such as lift/drag ratio, tip speed ratio, power coefficient, and torque coefficient.
Also, this paper presents a review of the aerodynamic performance of the recent VAWT designs to help researchers to identify and choose the best model among the Savonius and Darrieus rotors for further development or designing a new model at different wind conditions.
This comparison review shows that for a large scale HAWT upwind 3 bladed wind turbines are the most optimum.
The helical Savonius rotors perform better by having positive torque coefficient at all azimuth angles.
Moreover, helical Darrieus was found to produce lesser noise and suitable for conventional areas.
hybrid SavoniusDarrieus rotors can solve the self-starting challenge of the VAWTs, and they are suitable at low wind speeds.
At last, this review shows some of the recent hybrid Savonius-Darrieus rotors which would help to solve the low efficiency of Savonius rotor and self-starting challenge of Darrieus rotors.
Article History:
Submitted/Received 03 Oct 2021
First revised 08 Nov 2021
Accepted 11 Jan 2022
First available online 14 Jan 2022
Publication date 01 Apr 2022
____________________
A 2022 Tim Pengembang Jurnal UPI Keyword:
HAWT,
Renewable energy.
VAWT.
Wind turbine.
Eftekhari et al.
Aerodynamic Performance of Vertical and HorizontalA | 66
INTRODUCTION
Life on Earth for humans is going to be harder and more uncomfortable due to global warming effects.
Global warming happens due to the molecular structure of the greenhouse gasses (GHG) which entrap heat in the atmosphere and transfer this heat to the surface of the Earth, as a result, it would further warm the Earth.
This cycle of trapping heat causes an overall increment of global temperature.
The process is very similar to the way a greenhouse works.
Therefore, the gasses that create this effect are named greenhouse gasses (Darkwah et , 2.
Based on the collected data from Enerdata for Global Energy Statistical Yearbook 2020.
CO2 emissions are increasing almost every year globally, which endangers the future of the Earth and human life.
One way to reduce the impact of emissions caused by GHG is to use the renewal energy sources.
Clean energy is inevitable, making it interesting for researchers, scientists, and engineers to create other types (Kareem et al.
, 2022.
Irawan et al.
, 2021.
Putri et al.
, 2021.
Sihombing et al.
, 2021.
Fauziah et al.
, 2021.
Hidayah et al.
, 2.
Wind energy is one of the most well-known renewal energy Wind turbines are used to harvest the wind the energy.
The wind turbines' origin is uncertain, but the vertical axis wind rotors were invented around 200 BC in Sistan.
Iran.
In the twelfth century.
Europeans used and modified the Persian Vertical axis wind turbine and then created the traditional European horizontal axis wind rotor (Fleming & Probert, 1.
In 1891, the first horizontal axis wind turbine (HAWT) was designed and constructed in Denmark by La Cour.
Later in 1920 first vertical axis wind turbine (VAWT) was patented by a French engineer called Darrieus.
La Cour and Darrieus brought the new era for wind turbines, which with the developments through years of research, become the current HAWT and VAWT (Fleming & Probert.
There have been some recent developments on wind turbines (WT).
Components to increase their gearbox and generator efficiency, such as slip rings, brushes, pitch control, bearings, and cables.
Wang et al.
, .
Habibi & Yousefi-Koma .
Jung et al.
, and Karthikeyan et .
studied different aspects of WT enhancement which in result helped to increase the effective output power of a WT by increasing the aerodynamic efficiency of wind turbines.
Aslam Bhutta et al.
reviewed the different types of Savonius and Darrieus VAWT and the design methods but did not cover the hybrid Savonius-Darrieus VAWTs.
El-Zafry et al.
studied all types of VAWTs including the hybrid SavoniusDarrieus but did not cover many variations of each type to decide if there is any variation that has better performance.
All types of wind turbines are developing and the wind turbine machines, in general, are becoming more complex and flexible (Lakhal et al.
, 2017.
Fadl et al.
but, the HAWT is commonly known and utilized while the VAWT is relatively new and research is being conducted on it due to its advantages over HAWT (Islam et al.
, 2.
An overall comparison between HAWT and VAWT is presented in Table 1.
Based on previous studies (Anggraeni et al.
, 2020.
Al-Obaidi et , 2021.
Eftekhari & Al-Obaidi, 2019.
Eftekhari et al.
, 2020.
Al-Qassar et al.
, 2021.
Al-Obaidi, 2.
, the main objective of this review is to give a complete and comparative literature survey about the factors affecting the aerodynamics of wind turbines by presenting the mathematical modelling of lift-type wind turbines.
This paper intends to serve as a general reference for aerodynamic models and would help as a quick tool in analysing and estimating the aerodynamic properties of HAWT and VAWT.
The structure of this review paper is as follows: Section 2 reviews the wind turbines' output power factors and Betz limit.
Mathematical relations that are typical for most HAWT models are presented in Section 3.
Section 4 DOI: https://doi.
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shows the typical mathematical relations for VAWT and recent developments on VAWTs
designs along with their advantages and Finally, contributions followed by the conclusions of this review paper are summarized in Section
OUTPUT POWER IN WIND TURBINE
The wind speed is one of the main factors that directly affect the output power of a wind turbine, hence the first step for using a wind turbine in any area is to study and measure the wind speed.
The higher wind speed would result in higher output power.
This relation can be further understood through Equations .
To calculate the power in the wind or available power for a wind turbine.
Equation .
is used:
ycEyc = 2 y yuU y ya y ycO 3 The available power for HAWT and VAWT is calculated using Equations .
ycEyc = 2 y yuU y yuU y ycI2 y ycO 3 ycEyc = 2 y yuU y Ea y ya y ycO 3 where R is the radius of HAWT or the length of one blade of HAWT and h is the height of the blade, and D is the diameter of the VAWT (Figure .
For HAWT construction, the direction of the wind is essential since HAWT interacts with wind from one direction only, while VAWT interacts with wind from different directions which gives an advantage over HAWT.
However, the VAWT output power efficiency is known to be lower than HAWT (Akhmedov et al.
, 2.
To calculate the actual electrical output power of wind turbines produced by a wind turbine, the power coefficient of the wind turbine.
known as the coefficient of performance, must be determined or given (Libii, 2.
where is the density of air.
A is rotor swept area.
V is wind velocity (Sarkar & Behera.
Table 1.
Comparison between HAWT and VAWT.
Characteristics Electrical energy (Islam et al.
, 2.
Weight (Islam et al.
, 2.
Rotor orientation (Carrigan et al.
, 2.
Wind direction Wind speed range (Islam et al.
, 2.
Environmental impact (Islam et al.
, 2013.
Rezaeiha et al.
, 2.
Starting function (Feng et al.
, 2.
Variety (Thresher & Dodge.
Tjiu et al.
, 2.
Cost and construction (Feng et al.
, 2.
HAWT
A Higher electric energy harvesting A Harvest more electric energy from a given amount of wind compared to VAWT.
A Heavier
VAWT
A Produce up to 50% more electricity on an annual basis versus conventional turbines with the same swept area.
A Lighter A Horizontal A Vertical A Functions at specific wind direction.
(Not suitable for turbulent wind.
A 6 m/s Ae 25 m/s A Functions in all wind directions.
(Suitable for turbulent wind.
A 2 m/s Ae 65 m/s A Higher chance of bird collision Higher noise A Lower chance of bird collision Lower noise A Higher starting torque A Self-starting A 2 bladed A 3 bladed A Lower starting torque A Might require energy to initiate rotation A Has two major types with many A Higher A Lower DOI: https://doi.
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Aerodynamic Performance of Vertical and HorizontalA | 68 Figure 1.
The typical shape of wind turbines: HAWT .
and VAWT .
The captured mechanical energy by the wind blades converts to electrical energy via wind generators.
This conversion is influenced by the efficiencies, such as gearbox efficiency, generator efficiency, and electrical efficiency.
The total power conversion efficiency from the wind to electricity can be calculated using Equation .
yuCyc = yaycy y yuCyciyceycayc y yuCyciyceycu y yuCyceycoyce .
is the total power conversion is the power coefficient, is the gear efficiency, is the generator efficiency, and is the electrical efficiency.
So, the effective power output from a wind turbine is achieved from Equation .
ycEyceyceyce = yaycy y yuCyciyceycayc y yuCyciyceycu y yuCyceycoyce y ycEyc = yuCyc y ycEyc is the effective power output from a wind turbine.
Based on Equations .
, increasing the conversion efficiency and/or wind power efficiency of the wind turbine helps with the increase of the harvested output power.
Since the air density is almost constant at a given altitude, an increase of the wind power PW can be achieved by increasing the wind speed .
y locating the wind turbine in an area with higher wind spee.
and/or increasing the swept area of the rotor.
On the other hand, to increase the total power conversion efficiency, one or the combination of the power coefficient, gearbox efficiency, generator efficiency, or electrical efficiency must be increased.
In 1920 Albert Betz (Betz, 2.
, a German scientist, formulated the maximum efficiency of an ideal wind turbine rotor, known as AoBetz Limit.
Ao In 1976.
Bergey (Bergey, 1.
clarified that a British scientist with the name of Lanchester derived the same maximum in A Russian aerodynamic scientist.
Joukowsky, achieved the same maximum efficiency for an ideal wind turbine in 1920.
To honor all of their efforts, this ideal efficiency is known as the AoLanchester-BetzJoukowsky limit (Kuik, 2.
Based on this limit, any wind turbine cannot capture more 3% of the available wind energy.
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Cp max = 593 (Syrensen, 2.
To achieve this limit and to ensure that the disk acts as a drag device that reduces the stream velocity, the following assumptions are to be considered (Ranjbar et al.
, 2.
A thin rotor would be replaced by a stationary disc or actuator disc, where it extracts the energy from the passing .
An ideal condition where there is no rotational velocity in the wake.
The flow is frictionless.
Now, the general momentum theory shows the performance of disc is as follow Equation .
yaycE = 1 ycE yuUycO 3 yaya = 4yca.
Oe yc.
where yaya is the disc area and yca is the induction factor.
The induction factor is expressed using the following Equation .
yca= ycOOeycOycO where ycOycO is the wake velocity in the proximity of the disc, and V is the wind speed.
The maximum value of power coefficient.
CP is achieved from the extremum value of Equation .
, which can be obtained as yccyaycE = 4.
Oe yc.
Oe 3yc.
= 0
When an ideal rotor is designed and operated in a way that the wind speed at the rotor is 2/3 of the free-stream wind speed, it is at its maximum power production.
So, this means that when , power production is at maximum, in other words, power coefficient is maximum (Equation .
yaycE,ycoycaycu = 27 = 0.
HORIZONTAL AXIS WIND TURBINE
HAWT is the most common and popular type of wind turbine because HAWTs are more durable and more efficient than VAWTs.
This is why most of the large-scale wind turbines are horizontal-axis types (Wang & Zhuang, 2.
We will be reviewing two major types of HAWT.
1 Types of HAWT There are two types of HAWTs, an upwind wind turbine (UWT) which is a HAWT with blades facing the wind direction, while a downwind wind turbine (DWT) is a HAWT whose blades are facing opposite of wind direction (Figure .
Another difference between these two types is that UWT has a higher power coefficient than DWT.
This is due to the design of the DWT which leads to a low power coefficient (Wang et al.
, 2.
2 Aerodynamics of HAWT On designing the HAWT with the current technology, three-bladed is the most the reason behind that lies in a simple comparison between two-, three-, and four-bladed HAWT.
Four bladed costs so much that it would not be worth building.
These are the reasons why most large-scale WTs are HAWTs with a three-bladed design.
The two-bladed design would give the same performance as the three-bladed design by increasing the wind turbine's chord length by However, then the two-bladed rotate faster than the three-bladed, so it generates more noise, and the two-bladed outstand more stress due to the increment of apparent Moreover, 3-bladed HAWT with 50% peak efficiency .
aximum efficienc.
is the most efficient WT type among all other typeAos available WTs .
ee Figure .
(Schubel & Crossley, 2.
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DWT on left and UWT on right.
3 Mathematical Framework for HAWT Power Coefficient Reynolds number Re of airflow over an airfoil is expressed using Equation .
(Bayati et al.
, 2.
ycIyce = yuUycOycI yca ycOycI yca ya = yayco 2 yuUycO 2 ya.
The relative airflow velocity VR for a typical airfoil in a HAWT blade section is expressed in Equation .
where V is the free stream velocity, yu is the angular velocity, yc is the radial distance from the center of rotation (Giguyre & Selig, .
ya = yaycc 2 yuUycO 2 ya, ya where ycOycI is the relative airflow velocity, c is the airfoil chord length, yuN and v are respectively, the dynamic and kinematic viscosity of air.
ycOycI = Oo.
Oe yc.
)2 .
2 Airfoil lift forces, drag forces, and lift to drag ratio are presented in Equations .
respectively (Manwell et al.
, 2.
yuUycO 2 y.
ya = .
a yco .
yuUycO 2 y.
= ya yco .
ya ycc One of the key factors in wind turbine blade design is the tip speed ratio, yuI which is calculated using Equations .
(Manyonge et al.
, 2.
yuNycC = ycN y ycO 2yuUycI yuI= yuN ycC where yuNycC is the time T taken for one complete oscillation of the rotor blade times the velocity of the wind V and R in Equation .
is the length of the rotor blade.
Figure 3.
Blade element forces (Lef.
and velocities (Righ.
(Leishman, 2.
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(Malge & Pawar, 2.
2yuUycI yuI=ycO= yuN = ycO ycC By applying Blade Element Momentum Theory (BEMT), the equations of a wind turbine blade, power-coefficient of the wind turbine can be derived.
The BEMT equations are presented in Equations .
(Osei et , 2.
yu =yuoOeyu .
yaAyca yuayc = 2yuUyc 1Oeyca 4ycycnycu2 yuo ayco ycaycuycyuo yaycc ycycnycuyu.
ayco ycycnycuyuo Oe yaycc ycaycuycyu.
1OeycaA ya yaycE = yuI2 OyuI yuI3yc y.
Oe yc.
Oe ( yaycc ) ycaycuycyu.
ycc yuIyc .
where ycaA is the tangential induction factor.
Integrating Equation .
, gives Equation .
which is a simpler equation to analyze.
yuI ya yayco yaycE = 2 ycaA.
Oe ycc ycaycuycyu.
Oe yc.
( yuI4 yuI 4 Oe Ea ) .
In Equation .
the relationship between lift to drag ratio and power coefficient of a ya HAWT is shown.
In this equation yaycc is the yco inverse of lift to drag ratio, so by increasing the lift to drag ratio the expression .
Oe yaycc ycaycuycyu.
will be larger which results in a ya yco higher power coefficient.
Figure 4 shows the flow model used for the BEM analysis of HAWT.
Referring to this figure, another approach to the power coefficient of HAWT by using BEMT is expressed in Equations .
(Leishman, 2.
yc yc=ycI .
yaycy = yuayuI3 O0 ( yuoyayco Oe yaycc )yc 3 yccyc.
Once again in Equation .
, the impact of the lift coefficient in a wind turbine blade design is presented and the importance of a high lift to drag ratio for a wind turbine blade is shown.
As it is clear in this equation, with a higher lift coefficient and lower drag coefficient, the power coefficient will So, to design a HAWT blade it is essential to have a high lift to drag ratio airfoil to increase the power coefficient to eventually increase the output power of the wind turbine.
VERTICAL AXIS WIND TURBINE
1 Major Types The origin of wind turbines is uncertain, but the start of using wind energy was in Sistan.
Iran.
Vertical axis wind rotors were invented around 200 BC in Sistan.
Iran which was used as a windmill to harvest wind energy (Fleming & Probert, 1.
The 2D design of the vertical axis wind rotor in Sistan is shown in Figure 5 (Hejazi, 2.
Generally, the VAWTs come into two major Savonius-Rotor.
Darrieus-Rotor.
Savonius uses drag force to function, similar to the vertical axis windmills that were used in Sistan, and just like HAWTs, they have the selfstarting mechanism.
However, the Darrieus type mostly needs a starting mechanism since their blade design does not always create sufficient torque for rotation.
The Darrius type uses lift force to function which is similar to how the 2-bladed or 3-bladed HAWT works (Tjiu et al.
, 2015.
Wenehenubun et al.
, 2015,
Jadallah et al.
, 2.
The general shape of the specified type of VAWTs is shown in Figure 6.
2 Other Configurations of VAWT One of the advantages of VAWT over HAWT among other advantages is, taking wind from any direction and lower starting torque (Castellani et al.
, 2.
This advantage is one of the main reasons that the VAWT has more shapes and designs compared to HAWT.
Same as HAWT, getting close to the Betz limit is one of the main factors of designing a new VAWT (Yurdusev DOI: https://doi.
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, 2.
Another reason for coming up with a new or novel shape for a VAWT is to fulfill the design requirement for different geographical conditions such as low wind, high wind speed, urban area, or commercial There are several types and configurations of Savonius and Darrieus rotors based on recent research where each of them has its advantages and The advantages and disadvantages of the various configuration and designs of the Savonius and Darrieus types are presented in Tables 2 and 3, respectively.
Corresponding figures for different types of Savonius and Darrieus rotors are shown in Figures 7 and 8.
Figure 4.
Flow model used for BEM analysis for HAWT.
Front view of the disk (Lef.
and crosectional view .
(Leishman, 2.
Figure 5.
Side view .
and top view .
schematic of a windmill in Sistan.
Figure 6.
Main types of VAWT (Kumara et al.
, 2.
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April 2022 Hal 65-88 It can be concluded from Tables 2 and 3, that different researchers tried to improve the efficiency and power coefficient of the VAWTs to reach as close as possible to Betz All these new designs have their advantages and disadvantages, but among the mentioned Savonius rotors.
Helical Savonius rotor with full circular end plates had the better performance.
Even though the double stage rotors have shown a better performance compared to the single stage, but they take more material and consume more space so would not be suitable for some cases.
Using diffusers also increase the performance of the Savonius rotors but they must be placed in a specific location where the wind always comes from a specific direction which could be useful in some special cases where it would be used on top of buildings.
As for the mentioned Darrieus rotors, for large scale.
Darrieus Phi rotor is suitable because it has the best performance among the others.
For small scale wind turbines to be used in local areas.
Helical Darrieus rotors is more suitable because of their steady performance and lower noise compared to straight-bladed and Phi Darrieus rotors.
Table 2.
Different configuration of Savonius VAWT advantages and disadvantages.
Configuration Conventional Savonius rotor (Figure 7 A) (Menet & Rezende.
Conventional Savonius rotor with curtains (Figure 7 B) (Altan & Atlgan.
Altan et al.
Modified Savonius rotor without shaft (Figure 7 C) (Kamoji et al.
, 2.
Conventional Savonius rotor with Combined Conventional and elliptical blade (Figure 7 D) (Sanusi et al.
, 2.
Savonius wind turbine with double wind tunnels (Figure 7 F) (Promdee & Photong.
A A A Advantage Low starting Torque A Low angular velocity A Generating electricity at low and high wind speeds.
Best performance at a fixed rotor position = 60A.
Power coefficient increases by 38% at optimum curtain design.
( = 45A and = 15A, l1 = 45cm and l2 = 52c.
Higher maximum power coefficient compared to the conventional Savonius rotor with the value of CPmax = The maximum power coefficient of the combined blade is 11% more compared to the conventional blade.
The maximum power coefficient of the combined blade is 5.
5% more compared to the elliptical blade.
Generates 45-68% more voltage compared to the conventional Savonius VAWT.
Disadvantage Drag device Low efficiency Change in the curtains angle setting creates negative torque which reduces the power coefficient of the rotor.
Fixed wind direction.
Drag device Low efficiency Negative torque coefficient at rotor angles ranging from 135A165A and 315A-345A.
Drag device Low efficiency Drop-in performance with the use of endplates linking shaft.
Drag device Low efficiency Only within a specific wind angle Drag device Low efficiency DOI: https://doi.
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Different configuration of Savonius VAWT advantages and disadvantages.
Configuration Three-bladed and four- A bladed Savonius wind rotor (Figure 7 G) (Alit et al.
, 2017.
Saha et al.
, 2.
One-stage.
Two-stage.
A and three-stage with 5A twisted blade Savonius rotor (Figure 7 H) A (Saha et al.
, 2.
Advantage Three-bladed Savonius rotor higher A power coefficient compared to fourbladed.
Twisted blade Savonius rotors have A better performance compared to the conventional Savonius rotor due to its positive torque in all rotor angles.
Two-stage twisted Savonius with the A Maximum power coefficient of CPmax = 285 has a higher power coefficient compared to one-stage and threestage.
Disadvantage The two-bladed Savonius rotor has better performance and a higher power coefficient.
Drag device Low efficiency Consume more material and more cost for the two-stage and three-stage.
Drag device Low efficiency Table 3.
Different configurations of Savonius VAWT advantages and disadvantages.
Configuration Three straight-bladed Darrieus A rotors with upper and lower surface connectors.
(Figure 8 A) (Castelli et al.
, 2011.
Jadallah et , 2.
Straight-bladed Darrieus rotor with upstream deflector.
(Figure 8 B) (Stout et al.
, 2.
Side by side twin straight bladed Darrieus rotor (Figure 8 C) (Zanforlin and Nishino, 2016.
Jin et al.
, 2.
Three V-shape blade Darrieus A rotor (Figure 8 D) (Su et al.
, 2.
Advantage Exceed Betz limit 3 times during one rotor revolution.
At a 90A deflector angle, the maximum power coefficient is CPmax = 0.
20367 which is 1.
higher compared to the original model.
Twin straight-bladed Darrieus rotor has a higher maximum power coefficient compared to the isolated .
straightbladed rotor.
Configuration A has a higher maximum power coefficient compared to configuration B.
Cmax OO 0.
493 with a gap ratio of 2 and phase angle of 60A and a TSR of 1.
Both V-shape and inverted Vshape has higher maximum power coefficient compared to the straight blade.
When OIV = 0.
6 c, power coefficient increases by 20%.
The increment of the power coefficient is mostly on the middle section of the V-shape Disadvantage Lower average power coefficient compared to conventional three straight bladed Darrieus rotor.
Only suitable for wind with a specific wind direction.
Reduced power coefficient at different deflector Suitable for small-scale wind turbines.
Same as straight-bladed, the V-Shape blade there is energy loss on the blade tip region.
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Different configurations of Savonius VAWT advantages and disadvantages.
Configuration Darrieus Phi rotor ggbeater/curved roto.
(Figure 8 E) (Islam et al.
, 2008.
Tjiu et al.
Cross axis helical Darrieus rotor A (Figure 8 F) (Muzammil et al.
, 2.
Helical twist Darrieus rotor (Figure 8 G) (Patel and Sapariya, 2017.
Ali et A , 2.
A Straight blade Darrieus with A wingtip devices (Figure 8 H) (Mishra et al.
, 2.
J-shaped straight Darrieus (Figure 8 I) (Zamani et al.
, 2.
H-type Darrieus VAWT rotor with A winglets (Figure 8 J) (Cai et al.
, 2.
Darrieus Phi rotor .
roposkien A troposkien shape-VAWT & 100% shifted troposkien shape-VAWT (Figure 8 K) A (Hilewit et al.
, 2.
Advantage With the curvature ratio of 1, it has the highest maximum power coefficient of CPmax OO Cost-effective.
Collect wind energy from horizontal and vertical Suitable for low wind speed Steady output power during once rotor oscillation.
( Cp OO.
Lower noise compares to straight-bladed, therefore more suitable, and safer for local areas.
Higher lift with the endplates, therefore better aerodynamic Winglets decrease the induced Improves the self-starting Less turbulency and noise.
Remove the pressure side of the blades from the maximum thickness to the thrilling edge.
The power coefficient with winglet increased by 10-19% compared to the typical H-type More output torque at all azimuth angles compared to the typical H-type rotor.
Aerodynamic performance was improved near the region of the blade tips.
Model A achieved a higher max power coefficient compared to model B and the conventional phi rotor.
Model A performs better at a higher TSR range compared to model B and the conventional phi rotor.
Model B performs better at a higher TSR range compared to the conventional phi rotor.
Lesser cost on model A and model B.
Disadvantage Rotor height limitation.
Uneven wind velocity on the rotor blades.
Not suitable for high wind speed areas.
Suitable for small-scale wind turbines.
Lower Max power coefficient compared to the straight-bladed Darrieus and twisted bladed Darrieus rotors.
The end plates make the trailing vortices weaker.
Winglets increase the total Generates drag because of the J shaped blades A Adding the winglet could change the optimum TSR DoesnAot change the performance for every azimuth angle for each of the blades.
Reduce blade wake interactions on both models compared to the conventional phi rotor.
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Different configurations of Savonius rotor.
Figure 8.
Different configurations of Darrieus rotor.
3 Aerodynamics of VAWT Among VAWTs, the Darrieus types are more efficient and can produce more energy.
The main reason is because they have a higher power coefficient .
ee Figure .
The other difference between the Savonius and Darrieus types is that the Savonius rotors start at lower wind speed, while the Darrius type starts at higher wind speed.
However, in terms of aerodynamic performance, the Darrius type is more efficient than the Savonius type since the Darrius type has a higher power coefficient (Aslam Bhutta et al.
, 2.
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p- ISSN 2528-1410 e- ISSN 2527-8045 77 | Indonesian Journal of Science & Technology.
Volume 7 Issue 1.
April 2022 Hal 65-88 Figure 9.
Power coefficient for different wind power generators (Damota et al.
, 2.
4 Mathematical Framework for VAWT Power Coefficient yaycu = yayco ycaycuycyu yaycc ycycnycuyu yayc = yayco ycycnycuyu Oe yaycc ycaycuycyu VAWT with a lower aspect ratio can achieve a higher power coefficient.
Figure 10 shows the difference between a low and high aspect ratio VAWT.
The aspect ratio of a VAWT blade can be found with Equation .
where h is the height of the VAWT blade and R is the radius of the VAWT (Brusca et al.
, 2.
In these equations, yu is the angle of attack which can be calculated by Equation .
yaycIycOycN = ycI ycOycI = Oo.
cOyca ycycnycuyuE)2 (OycI ycOyca ycaycuycyuE)2 .
ycOyca = ycO.
Oe yc.
ycOycI = Oo(.
Oe yc.
ycycnycuyuE)2 ( .
Oe yc.
ycaycuycyuE)2 yca where ycOyca is the induced velocity, yui is angular velocity and R is the radius of the turbine, and yuE is the azimuth angle.
The normal coefficient yaycu and tangential coefficient yayc are expressed in Equations .
Now by using Equations .
into Equation .
Oeyc.
ycycnycuyuE From Figure 11, the relative airflow velocity ycOycI and induced velocity ycOyca are shown in Equations .
, wind speed is used to express the relative airflow velocity in nondimensional form.
ycO ycO ycycnycuyuE yca yu = ycycaycuOe1 [OycI ycO ycaycuycyuE yu = ycycaycuOe1 [ .
Oeyc.
ycaycuycyuE] .
There are three common momentum models for single-bladed VAWTs of Darrieus type which are the Single StreamTube model (SST).
Multiple StreamTube Model (MST), and Double Multiple StreamTube model (DMST).
Among these three models.
DMST is the best model because in this model vertical and horizontal velocity variations are considered across the stream tube while in the SST model the velocity is constant.
Even though in the MST model the velocity varies but the effect of the upwind part and downwind part is not considered.
That is why the DMST is the most complete model among these (Amin Mohammed et al.
, 2.
Figure 12 shows the difference between these stream tube models.
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Aerodynamic Performance of Vertical and HorizontalA | 78 Figure 10.
VAWT with different aspect ratios (Brusca et al.
, 2.
Double actuator disks are required to be positioned in series as is shown in Figure 13.
The velocity of the wind at the downstream equilibrium is ycOyce Now the induced velocity for both upwind ycOyca and downwind ycOycaycc are expressed in Equations .
(Mohammed et , 2.
ycOyca = ycO.
Oe yc.
= ycOOeycOyce .
ycOyce = ycO.
Oe 2yc.
Oeycaycc )ycycnycuyuE yu ycc = ycycaycuOe1 [ .
Oeycayc.
ycaycuycyuE].
The power coefficient of the upwind yaycEyc , the power coefficient of the downwind yaycEycc , and the total power coefficient yaycE can be determined by Equations .
respectively (Mohammed et , 2.
ycAycaya ycO OeycO ycc ycaycc = yce ycO yca yce As it is shown in Figure 14, the upwind side and downwind side are separated which means it will need 2 different equations to find the power coefficient of the upwind section and the power Coefficient of the downwind section and the total power coefficient will be the summation of these yuU 3yuU Now for the upwind section ( 2 O yuE O 2 ), the relative velocity ycOycI and the angle of attack yu ycOycI = Oo.
cOyca ycycnycuyuE)2 (OycI ycOyca ycaycuycyuE)2 .
Oeyc.
ycycnycuyuE yu = ycycaycuOe1 [ .
Oeyc.
ycaycuycyuE].
ycOycIycc = Oo.
cOycaycc ycycnycuyuE)2 (OycI ycOycaycc ycaycuycyuE)2 .
Then for the downwind section ( 2 O yuE O 2 ), the relative velocity ycOycIycc and the angle of attack yaycEyc = 2yuUya O yayc ( ycOycI )2 yccyuE , ycAycaya ycO ycO ycOycaycc = ycO.
Oe 2yc.
Oe ycaycc ) = yce 2 yc ycOycc yaycEycc = 2yuUya O yayc ( ycOycI )2 yccyuE, .
yaycE = yaycEyc yaycEycc .
In both Equations .
yayc is one of the main factors, by referring to Equation .
can notice the importance of high lift to drag ratio airfoils on designing a VAWT Darrieus type.
5 Hybrid (Combine.
VAWT Savonius-Darrieus Darrieus rotors have good aerodynamic performance but usually are not self-starting, while the Savonius rotors are self-starting but have low aerodynamic performance because the Savonius rotors will function with drag A combination of them or in other words hybrid Savonius-Darrieus rotor will help to solve the self-starting challenge for the Darrieus rotor and the low aerodynamic performance of the Savonius rotor (Liang et al.
, 2.
The advantages and disadvantages of the various configuration and designs of the hybrid Savonius-Darrieus are presented in Table 4.
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Volume 7 Issue 1.
April 2022 Hal 65-88 Figure 11.
Airfoil velocity and force diagram (Yao, 2.
Figure 12.
Development of stream tube theory.
SST in the .
MST in the .
and DMST in the .
(Mohammed & Mustafa, 2.
Figure 13.
Schematic of the two-actuator disk in tandem (SimonoviN et al.
, 2.
Figure 14.
Diagrammatic representation of DMST model (Mohammed et al.
, 2.
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p- ISSN 2528-1410 e- ISSN 2527-8045 Eftekhari et al.
Aerodynamic Performance of Vertical and HorizontalA | 80 Based on Table 4, the self-starting challenge of the Darrieus rotors were solved by mixing them with Savonius rotors, they will have lesser performance compared to the Darrieus rotors.
A factor which must be considered while making a hybrid SavoniusDarrieus rotor is the Savonius rotor should be placed inside the Darrieus rotor, because it extracts the wind better at short duration and it is more compact.
Among the mentioned Savonious-Darrieus Two-bladed Savonius with three-bladed helical Darrieus is the most recommended one because the model is not too complex, and the performance is relatively good.
Table 4.
Different configuration of hybrid Savonius-Darrieus VAWT advantages and Configuration Two-bladed Savonius with three-bladed straight Darrieus (Figure 15 A) (Nemati, 2.
Two-bladed Savonius with three-bladed helical Darrieus (Figure 15 B) (Pallotta et al.
, 2.
Double stages two-bladed Savonius with egg beater Darrieus (Figure 15 C) (Wakui et al.
, 2.
Double stages two-bladed Savonius with two, three, and four-bladed straight bladed Darrieus (Figure 15 D) (Ahmedov, 2.
Three-bladed Savonius and thirteen-bladed Darius (Figure 15 E) (Boz et al.
, 2.
Combined Bach-type and HDarrieus rotor (Figure 15 F) (Hosseini & Goudarzi, 2.
A A A A A A A A Advantage Better performance compared to Darrieus rotor.
It performs well at low TSR.
Unlike the Darrieus rotor, it can function at low wind speed.
20% less starting speed compared to Helical Darrieus alone.
(At 3 m/s wind spee.
Higher Performance compared to Savonius rotor alone.
Self-starting.
Type B extracts more output power from wind in small scale and long wind blowing duration, but Type A can extract better in the short wind blowing duration.
Type A is more compact and is more suitable for local areas.
Self-starting.
Better efficiency with three blades compared to two and four-bladed Optimum power coefficient for the hybrid device at 0A.
Self-starting.
CP OO 0.
Better performance compared to Darrieus rotor.
Wind focusers .
he orange bottom and top sectio.
helped to increase the energy production by 8%.
Self-starting.
Cpmax OO 0.
41 which is 54% higher than the Savonius rotor alone.
Self-starting.
Disadvantage Complex geometry.
Straight Darrieus has better 20% performance compares to the Helical Darrieus rotor alone.
Lower output power compares to the Darrieus rotor alone on both models.
Type B has a longer startup Type B has lower performance.
Darrieus rotor alone has better performance and a higher power coefficient.
With 4 Darrieus blades it has better self-starting but a lower maximum power coefficient.
Complex geometry.
Costly design due to the complexity of the design and the quantity of the blades.
Darrieus rotor alone has 17% higher Cpmax compared to the hybrid model Complex model and higher cost because of the multiple Darrieus and Savonius rotors.
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p- ISSN 2528-1410 e- ISSN 2527-8045 81 | Indonesian Journal of Science & Technology.
Volume 7 Issue 1.
April 2022 Hal 65-88 Figure 15.
Different configurations of hybrid Savonious-Darrieus rotor.
CONCLUSION
The available data on global warming shows the necessity of replacing fossil fuel power plants with green energies.
Wind energy is a great solution for the global warming challenge as wind is a free source of energy and it does exist at any place on the Yet choosing the right wind turbine at the right place is always the challenge, because transporting and installing large scale wind turbines is challenging on some Yet using the small scale or micro wind turbines is easier but it is less efficient.
The advantages of HAWTs over the VAWTs are as follow:
A Harvest more energy from a specific wind A Higher power coefficient.
A Self-starting.
And the VAWTs advantages over the HAWTs are:
A Relatively lesser noise.
A Suitable for turbulent wind.
Does not harm birds while rotating.
Less cost for transportations and A Can accept wind from all directions.
Based on the findings of this review paper, the following criteria may be used to improve the performance of the Savonius rotors:
A Helical/Twisted blades A Full circular end plates A Two-staged blades As for the Darrieus the following criteria is suggested to performance of the rotor:
Darrieus at low wind speed o Cross axis helical Darrieus rotor o Side by side twin straight bladed o Darrieus rotor o Helical twist Darrieus rotor .
Darrieus at high wind speed:
o Straight-bladed Darrieus o Darrieus Phi rotor .
ggbeater/curved One of the methods to increase solve the self-starting challenge of Darrieus rotors and low efficiency challenge of Savonius rotor is to DOI: https://doi.
org/10.
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p- ISSN 2528-1410 e- ISSN 2527-8045 Eftekhari et al.
Aerodynamic Performance of Vertical and HorizontalA | 82 use hybrid Savonius-Darrieus rotors.
There is so much potential in wind turbine technologies which is yet to be discovered by researchers to achieve as close as possible to Betz Limit to achieve higher power coefficient and in result higher output power from wind AUTHORSAo NOTE The authors declare that there is no conflict of interest regarding the publication of this article.
The authors confirmed that the paper was free of plagiarism.
REFERENCES