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... The torque coefficient (C m ) is usually expressed as [48]: ...

... The power coefficient (C p ) is the ratio of output power to input power, and is calculated as shown in equation (4) [48]. The value of C p is the most prominent factor in determining the performance of a SHKT, and hence has been used as the basis of optimization in the present work. ...

... The numerical simulation was performed in ANSYS Fluent 19.2. The modelling consists of continuity and momentum equation along with Fig. 2. Parameters of SHKT turbulence model equation, given as follows [48,50]: ...

The Savonius Hydro-Kinetic Turbine (SHKT) has a frugal design with the possibility of easy local manufacturing. Therefore, SHKT is a suitable proposition for off-grid power generation in standalone mode across the remote and hilly locations. In this work, an optimized geometry of a semicircular SHKT was proposed through 3D CFD based simulations, artificial neural network (ANN) augmented optimization and experiments. Firstly, CFD investigations of SHKT were performed to identify the parameters affecting the power coefficient (Cp). Results of CFD simulations were used to train ANN which was further used to optimize the blade parameters. Finally, experiments were conducted on the optimized blade to validate its performance. The results showed that aspect ratio between 1.4 and 2.0 and overlap ratio between 0.15 and 0.2 indicate better performance. Blade arc angle of 166° produced a maximum Cp of 0.194 at a TSR of 0.8. The study concluded that ANN is a time saving yet accurate tool for optimization of turbine blades, and the results provide a good agreement with the computational results with difference of 1.57% only. The optimized blade is found to be 8% more efficient than semicircular blades and is recommended for its applications in hydro farms and turbine clusters.

... They also developed a correlation for a single stage modified savonius rotor to predict the moment coefficient in terms of Reynolds number and tip speed ratio. El-Baz et al. [9] investigated the performance of a three-rotor savonius turbine using computational fluid dynamics (CFD). The results showed that the average moment coefficient and the power coefficient of the three-rotor turbine are higher than those of the single rotor turbine. ...

... Sliding mesh model is applied to obtain the rotating motion of the turbine. The enhanced wall function method is applied to ensure the precise resolution of the boundary layer prediction [9]. The wall function approach requires the dimensionless distance of the first grid point from the wall (y+) to be greater than 30, which is used in the present work. ...

... The torque coefficient is getting stable and constant after 130,000 cells and whatever the increase in a number of cells. Moreover, the time step size is considered as in El-Baz et al. [9]. ...

Savonius hydrokinetic rotor is an evolution of the conventional savonius wind turbine. This rotor is suitable for low flow velocities with simple design, high starting torque and working for all flow directions. However, the torque fluctuation of this rotor is a serious problem due to the negative moment generated at the returning blade of this rotor. In this paper, a numerical investigation with commercial computational fluid dynamic (CFD) package FLUENT for modified savonius rotor with two deflector plates in the upstream of the turbine is conducted to find the optimum position of the two deflector plates to increase the power coefficient using water as a working medium. Results show that the model with the best orientation of the two deflector plates in the upstream increases the power coefficient by 80%. This may be due to the overlapped effect of decreasing the negative moment on the returning blade and the increased flow velocity at the advancing blade.

... Patel et al. [14] have also carried out experimental investigation to obtain the optimum stream wise and span wise distance on the performance of the Darrieus type of hydrokinetic turbine. Similarly, El-Baz et al. [15] have suggest the improved three rotor configuration with CFD simulations for Savonius wind turbine application. ...

... Different correction methodologies are reviewed by Ross and Altman [15] to study the influence of blockage. Maskell [26] has studied the influence of blockage for bluff bodies. ...

... Alexander provided an improved method of Maskell's method by comparing the drag of flat plates normal to the free stream with the drag of Savonius turbines normal to the free stream [13]. The graphical relationship for the Savonius turbines indicated by Ross and Altman [15] is digitized and with appropriate curve fitting, following relation is obtained between m and blockage ratio (BR) [5]. Eq. (120), corrected local velocity is obtained by the Eq. ...

... It was deduced that the torque generated from the wind turbine is directly proportional to the cube of rotor diameter, while the aerodynamic forces increase with the square of the diameter [9]. New wind turbines designs were proposed and studied for the same purpose of ameliorating their efficiency [10][11][12][13][14][15][16][17][18]. El-Baz et al. [11] suggested an optimized Savonius wind turbine system design comprising three turbine rotors arranged in a triangular pattern. ...

... New wind turbines designs were proposed and studied for the same purpose of ameliorating their efficiency [10][11][12][13][14][15][16][17][18]. El-Baz et al. [11] suggested an optimized Savonius wind turbine system design comprising three turbine rotors arranged in a triangular pattern. They found that the performance was improved significantly compared with the single rotor design. ...

This paper aims to enhance the performance of H-Darrieus Vertical Axis Wind Turbine (VAWT) via introducing upstream deflectors. The impact of this addition has been investigated and discussed through different deflector configurations. The turbine performance before and after adding different wind rotor barriers was compared. A two dimensional, incompressible, transient, and turbulent flow model was built up in order to simulate the air flow around the turbine blades. Model verification and validation were performed through comparing the model solutions using different mesh sizes, time steps, turbulent models, and discretization schemes. Computational Fluid Dynamics (CFD) models were validated to provide novel insights on the effect of the deflectors on the aerodynamic characteristics of a VAWT blades. Results showed that the presence of a single deflector increases the highest value of the moment coefficient of the bare configuration by 24%, either increases the negative torque values, while two defectors increase the maximum value by 22% and the overall average value of the moment coefficient over the optimal range for the tip speed ratio.

... Shigetomi et al. [33] studied the interaction of flow fields around two Savonius turbines. El-Baz et al. [34] reported 44% increase in power coefficient, when three Savonius turbines were arranged in a triangular pattern. Tartuferiet al. [34] investigated the effect of blade shapes. ...

... El-Baz et al. [34] reported 44% increase in power coefficient, when three Savonius turbines were arranged in a triangular pattern. Tartuferiet al. [34] investigated the effect of blade shapes. The optimized blade shape can achieve a maximum C p of 0.301 and curtain systems increased the power output by 20%. ...

Large-scale industrial wind turbines are well developed and widely implemented to harness kinetic energy of air flow for power production. However, little attention and effort was paid on developing miniature energy-efficient wind harvesters. In this work, a miniature harvester driven by air flow was manufactured by applying 3D printing technique and experimentally evaluated in a closed-loop wind tunnel. To simulate the experiment and to optimize the wind harvester design, three-dimensional numerical study was conducted. The model was validated by comparing the experimental results with the numerical ones first. Parametric study was then experimentally and numerically performed to examine the critical roles of (1) type of central part, (2) presence of end plates, (3) harvester length, (4) harvester diameter, (5) number of blades and (6) harvester installation orientation on static and dynamic performances of the designed harvesters. The optimal design was achieved according to the overall energy conversion efficiency, and the maximum efficiency achieved was η max = 6.59%.

... Regarding the three rotors cluster of Savonius turbines, the authors found that the configuration with two rotors positioned upstream and one rotor downstream demonstrated the highest performance, the optimal configurations of the two wind turbines in parallel and oblique being applied. Likewise, El-Baz et al. (2016) conducted an evaluation of the efficiency of three Savonius rotors assembled in a triangular configuration. They performed 2D numerical computations based on the implementation of the Reynolds averaged Navier-Stokes equations and the realizable k- turbulence model, with a sliding mesh technique. ...

CFD investigation is conducted in the present study to analyse the effect of wind lenses on the aerodynamic performances of a vertical-axis wind turbine (VAWT). the case of a 2D Savonius bi- blade is considered, where different configurations of wind lenses are studied and compared. To simulate the fluid flow over a rotating wind turbine, unsteady 2D numerical computations are carried out to solve the Reynolds Averaged Navier Stokes equations (URANS), where the turbulence is modeled by the SST k− ω model. The results demonstrate an increase in the power coefficient across various tip speed ratios when wind lenses are utilised. Additionally, the study analyses the wake patterns generated by both conventional open turbines and turbines integrated with wind lenses.

... Regarding the three rotors cluster of Savonius turbines, the authors found that the configuration with two rotors positioned upstream and one rotor downstream demonstrated the highest performance, the optimal configurations of the two wind turbines in parallel and oblique being applied. Likewise, El-Baz et al. (2016) conducted an evaluation of the efficiency of three Savonius rotors assembled in a triangular configuration. They performed 2D numerical computations based on the implementation of the Reynolds averaged Navier-Stokes equations and the realizable k- turbulence model, with a sliding mesh technique. ...

The aim of this study is to evaluate the aerodynamic efficiency of a Savonius vertical-axis wind turbine. The approach used relies on resolving the Unsteady Reynolds Averaged Navier-Stokes equations (URANS), the turbulence being modeled by the k-ω SST model. The flow around the wind turbine is simulated using the arbitrary sliding interfaces technique. First, the study investigates the impact of blade shape on wind turbine efficiency by examining seven Savonius rotors constructed with distinct blade configurations. The results indicate that the highest aerodynamic performance is provided by the rotor with the elliptical blades, with a notable increase in the power coefficient of about 80% in comparison to the classic semi-circular profile. To further enhance the efficiency of the Savonius wind turbine, a twin-rotor configuration using the elliptical blades was studied. The results indicate a further enhancement in the power coefficient, reaching 110% compared to a single rotor with semicircular blades.

... Recent studies have indicated that the interactions between Savonius wind turbines in a cluster can significantly enhance the output power of individual rotors. This effect leads to improvement in the performance and efficiency of the turbines, resulting in a substantial increase in their power generation (14,15). To improve the aerodynamic performance of Savonius wind rotors, two different approaches have been introduced: the use of innovative airfoil-shaped blades and a new curtain system (16). ...

... Another disadvantage of drag turbines is the efficient use of half of the space occupied by the rotor. Although wind technology begins with drag-type mills, in practice, these inherent flaws have hindered the development of more advanced species [40,41] . ...

Increased concern for the environment has led to the search for more environment-friendly energy sources so that wind energy can be used as an endless option for human consumption. Wind turbines offer a promising solution for off-grid areas. However, they have certain drawbacks associated with different configurations. Darrieus turbine is one type that can be more efficient than other types. The poor start-up performance of Darrieus turbines is one of the critical problems restricting its development. Another problem of this kind of wind turbine is tackled by identifying the optimization parameters, such as complex flow dynamics around the system. The present article reviews modeling vertical axis turbines methods and discusses the turbine's operation by presenting the results of these methods. In this review, the authors have attempted to compile the main aerodynamic models that have been used for performance prediction and design of straight-bladed Darrieus-type VAWT. The main object of this study is to research the advantages and disadvantages of wind turbine modeling methods, and the selection of these methods depends on the purpose of the modeling.

... Another disadvantage of drag turbines is the efficient use of half of the space occupied by the rotor. Although wind technology begins with drag-type mills, in practice, these inherent flaws have hindered the development of more advanced species [40,41] . ...

p> Increased concern for the environment has led to the search for more environment-friendly energy sources so that wind energy can be used as an endless option for human consumption. Wind turbines offer a promising solution for off-grid areas. However, they have certain drawbacks associated with different configurations. Darrieus turbine is one type that can be more efficient than other types. The poor start-up performance of Darrieus turbines is one of the critical problems restricting its development. Another problem of this kind of wind turbine is tackled by identifying the optimization parameters, such as complex flow dynamics around the system. The present article reviews modeling vertical axis turbines methods and discusses the turbine’s operation by presenting the results of these methods. In this review, the authors have attempted to compile the main aerodynamic models that have been used for performance prediction and design of straight-bladed Darrieus-type VAWT. The main object of this study is to research the advantages and disadvantages of wind turbine modeling methods, and the selection of these methods depends on the purpose of the modeling. </p

... The ANSYS Fluent 19.2 simulation software was used for the calculations. Equations of continuity and momentum, as well as the turbulence model, are used in this modelling, given as follows [35,36]: ...

... Another disadvantage of drag turbines is the efficient use of half of the space occupied by the rotor. Although wind technology began with drag-type mills, in practice, these inherent flaws have hindered the development of more advanced species [13,14]. ...

Wind energy can be used as an inexhaustible option for human consumption. Wind turbines offer a promising solution for off-grid areas. Darrieus turbine is one of the types of turbines that can be more efficient than other types if it is used by knowing its characteristics. The complex dynamic mechanism of the flow around the machine has led to its aerodynamic optimization problems remaining complex. This article reviews the applied methods in modeling vertical axis turbines and implicitly shows the turbine operation by presenting the results of these methods. Knowing these methods is important because each has its advantages and disadvantages and should be selected depending on the purpose of the research. One of the problems with Darrieus turbines is their poor start-up, which has been little researched so far. Finally, a suitable method that can model the start-up is introduced.

... The man-made irrigation channel is suitable for hydrokinetic power generation due to availability of sufficient water velocity, depth of water, and less debris (leaves, branches, logs) (Aisenbiey et al., 1978;Anyi and Kirke, 2010;Kerikous and Thévenin, 2019a;Khan et al., 2008;Kumar and Saini, 2016;Patel et al., 2016;Salleh et al., 2019). A small scale independent, pressure-driven Savonius turbine (Wahyudi et al., 2015;Yao et al., 2013) can be utilized to produce electrical power for domestic applications, like water pumps, charging batteries, fueling broadcast communications, and a few other low power applications (Al-Bahadly, 2009;Birjandi et al., 2013;Doso and Gao, 2020;El-Baz et al., 2015;Menet and Bourabaa, 2004;Patel et al., 2016;Ramadan et al., 2020). Since its invention in 1920, many efforts were carried out to enhance the turbine performance. ...

In the present paper, three-dimensional numerical simulations were carried out to examine the influence of the overlap ratio between the two straight edges on the advancing and returning blades of the novel V-shaped rotor blade profiles using the sliding mesh technique. The performance parameters were computed with respect to the tip speed ratio. The findings show that the coefficient of torque and power for the novel V-shaped turbine blade is maximum for the zero-overlap ratio compared to the turbine blade, with an overlap ratio ranging from 0.05 to 0.3. The blade profiles' flow field was visualized at different angular positions, and various significant zones developed during the turbine blade rotation were captured and analyzed. The new overlapping jet developed between the two straight edges of the advancing and returning blade profiles as the overlap ratio varies from 0.05 to 0.3. Therefore, the turbine's performance is reduced due to the development of an overlap jet as it travels parallel to the straight edges of the blade profile and does not impact the rear side of the returning blade profile.

... An up to 37% increase in C P was obtained for the optimal cluster at a TSR of 0.8. El-Baz et al. [25] investigated the performance of a three Savonius turbine cluster located in a specific isosceles triangle with the same initial phase angle and speed, but the rotational directions of turbines are different. An increase of up to 44% in C P was obtained, compared with that of an isolated turbine, and the evident performance improvement was attributed to the high-speed flow accelerated by the favorable interaction between turbines. ...

The average power output of multiple Savonius wind turbines optimally arranged in a cluster is improved significantly compared to that of an isolated turbine due to the coupling effect. Previous investigations focused on the influence of the configuration and the initial phase angles of Savonius turbines operating at the same rotational speed in a cluster. This paper proposes to adopt the variable-speed control method to improve the power output of a three-turbine cluster, and simultaneously avoid the requirement for the accurate initial phase angle settings of the turbines. The Taguchi method is used to optimize the configuration of the cluster. The distances between the centers of adjacent turbines (L1-2, L1-3), the configuration angles (θ1-2, θ1-3), and the combination of rotational directions (RD) are taken as Taguchi experimental factors. The optimal configuration of the cluster is determined to be L1-2 = 2.0D, L1-3 = 2.4D, θ1-2 = 110°, θ1-3 = 110°, and RD = (-,+,-). The influence strength of the factors is ranked as configuration angle, RD, and distance between turbines. In addition, the average power coefficient of the turbines in the optimal cluster is 1.425 times that of an isolated turbine and the tip speed ratios of the three turbines are 1.13, 1.14, and 1.09.

... The lift-type VAWT with a high speed has excellent aerodynamic characteristics at a high wind speed, while its starting characteristics are always unsatisfactory [7,8], which results in unsatisfactory aerodynamic characteristics of this type of wind turbine [9][10][11][12]. The drag VAWT has a suitable starting moment at a low wind speed, but the low revolving speed is unable to surpass the wind speed; thus, it is a sub-wind speed rotor, whose power coefficient of wind energy is lower at a high tip speed ratio [13][14][15][16][17]. In view of the characteristics of the two types of VAWTs, in order to develop their application, a large number of scholars are devoted to combining the two types by using a VAWT with semi-circular or savonius drag blades as the built-in starter of a lift-type VAWT to compose a lift-drag combined one, thereby optimizing the starting characteristics of the lift-type VAWT to enhance the performance of the VAWT. ...

In order to get rid of the impact of the global financial crisis and actively respond to global climate change, it has become a common choice for global economic development to develop clean energy such as wind energy, improve energy efficiency and reduce greenhouse gas emissions. With the advantages of simple structure, unnecessary facing the wind direction, and unique appearance, the vertical axis wind turbine (VAWT) attracts extensive attention in the field of small and medium wind turbines. The lift-type VAWT exhibits outstanding aerodynamic characteristics at a high tip speed ratio, while the starting characteristics are generally undesirable at a low wind speed; thus, how to improve the starting characteristics of the lift-type VAWT has always been an important issue. In this paper, a lift-drag combined starter (LDCS) suitable for lift-type VAWT was proposed to optimize the starting characteristics of lift-type VAWT. With semi-elliptical drag blades and lift blades equipped on the middle and rear part outside the starter, the structure is characterized by lift-drag combination, weakening the adverse effect of the starter with semi-elliptical drag blades alone on the output performance of the original lift-type VAWT and improving the characteristics of the lift-drag combined VAWT. The static characteristic is one of the important starting characteristics of the wind turbine. The rapid development of computational fluid dynamics has laid a solid material foundation for VAWT. Thus the static characteristics of the LDCS with different numbers of blades were investigated by conducting numerical simulation and wind tunnel tests. The results demonstrated that the static torque coefficient of LDCS increased significantly with the increased incoming wind speed. The average value of the static torque coefficient also increased significantly. This study can provide guidelines for the research of lift-drag combined wind turbines.

... The man-made irrigation channel is suitable for hydrokinetic power generation due to availability of sufficient water velocity, depth of water, and less debris (leaves, branches, logs) (Aisenbiey et al., 1978;Anyi and Kirke, 2010;Kerikous and Thévenin, 2019a;Khan et al., 2008;Kumar and Saini, 2016;Patel et al., 2016;Salleh et al., 2019). A small scale independent, pressure-driven Savonius turbine (Wahyudi et al., 2015;Yao et al., 2013) can be utilized to produce electrical power for domestic applications, like water pumps, charging batteries, fueling broadcast communications, and a few other low power applications (Al-Bahadly, 2009;Birjandi et al., 2013;Doso and Gao, 2020;El-Baz et al., 2015;Menet and Bourabaa, 2004;Patel et al., 2016;Ramadan et al., 2020). Since its invention in 1920, many efforts were carried out to enhance the turbine performance. ...

Hydrokinetic technologies harvest renewable power by harnessing the kinetic energy of water from free-flowing rivers, streams, dam head/tailrace and irrigation channels. Savonius rotor is one of the simple and low-cost vertical axis drag type devices used for the extraction of hydrokinetic power. The main limitation of Savonius hydrokinetic turbine is its low efficiency due to negative torque developed by the returning blade without augmentation techniques. In this paper, an experimental investigation is carried out in a multipurpose tilting water flume using V-shaped rotor blade profiles by maintaining a fixed V-angle of 90°, varying length of V-edges, arc radius and with a constant aspect ratio of 0.7. The simulations were carried out using commercial software, ANSYS Fluent. From the experimental and numerical results, it was found that, the optimum blade profile (V4) has developed a maximum coefficient of power 0.22 and 0.21 respectively, at a tip speed ratio 0.87. It was found that, the maximum coefficient of power of optimal V-shaped blade profile (V4) is 19.3% higher than the semi-circular blade profile.

... The non-vented elliptical-bladed rotor has C p greater than that of the conventional semi-circular-bladed rotor by 16.31% and the vented elliptical-bladed rotor has C p greater than that of the conventional semi-circular-bladed rotor by 23.06% [7]. The peak C p of the three-rotor Savonius turbine with rotors arranged in a triangular pattern is approximately 44% higher than that of the single rotor design [8]. The developed three turbine cluster has an average C p up to 34% higher than that of an isolated turbine [9]. ...

... The unsteady performance of the turbine rotor is simulated with a constant inlet velocity, while changing the rotor rotational speed to obtain different tip speed ratios. The time step (Δt) is set for each rotational speed corresponding to an azimuthal angular step (Dq) based on Ref. [59]. Each physical time step is set to perform about 30 sub-iterations in order to obtain a converged solution in the simulations. ...

Wind-lens turbines (WLTs) exhibit the prospect of a higher output power and more suitability for urban areas in comparison to bare wind turbines. The wind-lens typically comprises a diffuser shroud coupled with a flange appended to the exit periphery of the shroud. Wind-lenses can boost the velocity of the incoming wind through the turbine rotor owing to the creation of a low-pressure zone downstream the flanged diffuser. In this paper, the aerodynamic performance of the wind-lens is computationally assessed using high-fidelity transient CFD simulations for shrouds with different profiles, aiming to assess the effect of change of some design parameters such as length, area ratio and flange height of the diffuser shroud on the power augmentation. The power coefficient (C p) is calculated by solving the URANS equations with the aid of the SST k-ω model. Furthermore, comparisons with experimental data for validation are accomplished to prove that the proposed methodology could be able to precisely predict the aerodynamic behavior of the wind-lens turbine. The results affirm that wind-lens with cycloidal profile yield an augmentation of about 58% increase in power coefficient compared to bare wind turbine of the same rotor swept-area. It is also emphasized that diffusers (cycloid type) of small length could achieve a twice increase in power coefficient while maintaining large flange heights.

... To enhance the performance at high wind speed and harvest energy at low wind speed, a CFD study has been performed to analyze the effect of wind boosters on power generation of vertical axis wind turbines Leephakpreeda, 2015, 2016). Shigetomi et al. (2011), Shaheen et al. (2015, and El-Baz et al. (2016) proved that the interactions between Savonius wind turbines in a cluster increased the output power of an individual rotor. A guide-box tunnel was also employed to prevent the rotor from strong wind disaster (Irabu and Roy, 2007). ...

The purpose of the present study is to enhance significantly the Savonius Bach-type rotor performance. This was achieved by adding a new stator around it. The stator is composed of three parts: shield, obstacle, and guide plate. A comprehensive parametric study was performed in which eight geometrical parameters for the stator were varied. One factor at a time method was utilized to find the stator optimum shape that achieves the maximum rotor power coefficient value. A 2D numerical model was employed using ANSYS Fluent 18.1. The dominant parameters that affect the aerodynamic performance of the turbine were demonstrated. According to the examined conditions, the results revealed that the maximum power coefficient for the rotor with optimum stator configuration achieved a value of 6 times greater than that of the bare rotor. It was concluded from this parametric study that the main effective element in the turbine stator is the stator obstacle. This study may be an important issue for further enhancement of the Savonius turbine's performance.

... The torque coefficient is getting stable and constant after 130,000 cells and whatever the increase in several cells. Moreover, the time step size is considered as in El-Baz et al. (2016). ...

River current energy is considered as the greenest energy available, as it has enormous energies stored. It is a promising energy source in renewable energy according to its accessibility and availability of the sources worldwide during the whole year. The Nile River in Egypt has been chosen as a case study for this type of energy and its availability in this paper. Nile River is considered and counted as an auspicious area; in particular along Upper Egypt, to produce electrical energy from the water current energy. This type of renewable energy is mightily recognized as unparalleled and unorthodox solution for the electric power demand in the remote areas of Upper Egypt. The process of hydrokinetic energy conversion utilizes the stored kinetic energy in the river stream which can be captured by a submerged hydrokinetic turbine of vertical axis type (VAT). Since VATs offer some specific advantages, it has been chosen to be the system of conversion for the water current energy into useful electric power. The main objective of this work is to investigate experimentally the performance of two different Savonius rotor profiles inline irrigation canal in Toshka, Aswan, Egypt. The rotor with better fullness has better operating characteristics with a power coefficient 0.1285 at tip speed ratio 0.61 which is higher than the other rotor profile by 12%.

... They found that the maximum power can be extracted when the rotor is positioned at 45° & 90° with respect to the incoming flow. El-Baz et al., [21] introduced a new arranged design using multi-Savonius turbines. They concluded the novel triangular arrangement increased the power coefficient by about 44%. ...

The Savonius wind turbine is considered as one of the solutions for harvesting the kinetic energy from the wind in the urban areas, due to magnificent features such as, low construction cost, high starting torque, and self-starting ability especially at low wind speed. However, the conventional rotor suffers from low efficiency. Thus, modifying the configuration of the rotor may be an effective solution for providing electricity to the communities with no access to the power grid. Thus, this investigation aims to study numerically the effect of adding two inner blades on the performance of the Savonius wind rotor at low tip speed ratios (TSRs). The simulations are carried out using the two-dimensional simulation with the assist of ANSYS software. For turbulence modelling, the K-ε/realizable model was adopted in this study. Power coefficient (C p) and torque coefficient (C t) at various TSRs for the rotor are determined under a constant external overlap of 0.018 m. Furthermore, the effect of space between the inner blades was also investigated using three values of spacing. The simulation results show that the rotor with two inner blades performs better than the same rotor without inner blades at all tested TSRs expect at low considered values of 0.2 and 0.25. The heights Cp was 0.188 with 17.1% performance improvement at TSR = 0.4. Furthermore, the numerical results show that C p values decrease with the decrease of the space between the blades.

... Cuerva and Sanz Andres [26] proposed an 146 extended formulation of the power coefficient of a wind turbine, which is the generalization 147 of the Betz Lanchester expression for the power coefficient as the function of the axial 148 deceleration of the wind speed. Numerical simulation is a very useful tool to investigate 149 different parameters [27] like moment of inertia [28], flow instability [29], rotor 150 configurations [30], length of the blade and blade angle [31], twisted vane [32], J shaped 151 straight vane [33], aspect ratio and solidity [34] etc. on the performance of the Savonius or 152 Darrieus turbine. However, with numerical simulations, it is difficult to investigate the effect 153 of change of free surface contour on the performance of the hydrokinetic turbine. ...

The aim of the present work is to study the influence of channel geometrical parameters on the performance of Savonius type hydrokinetic turbine and to present velocity correction methodology to determine the actual performance of the turbine. In the present experimental work, the effect of geometry of channel bottom and channel side wall distance on the performance of a Savonius turbine is investigated. Elevated channel bottom (hump) enhances the velocity of flow by reducing the depth of flow. Experimental results indicate that nearly an increase of 83% in power output is achieved by placing the turbine on the hump with reference to the turbine placed at the bottom of the channel. Similarly, the effect of channel sidewall location on the performance of turbine is studied for two separate cases, i. Constant flow rate - water spilling not allowed from blocked region and ii. Variable flow rate -water spilling over the blocked region allowed. In both the cases, the obtained coefficient of power is achieved above 0.45, considering the inlet velocity of flow. The results suggest that the potential head difference between the turbine inlet and outlet has the predominant effect on the power output of the turbine when a rotor is placed between the two closely located side walls.
Considering the above facts, a new methodology is developed to find the corrected velocity to correlate the results obtained from restricted, high blockage canal flow with the performance which can be obtained from the same turbine when operated in a negligible blockage flow domain. Experimental results indicate that there is a vast variation in the maximum coefficient of power for all the cases studied if the velocity correction is not considered. However, with the application of the present velocity correction method, the corrected results are closer with the unblocked case.
Keywords
Savonius turbineHydrokinetic turbineMaskell's correctionblockage effectchannel parametersvelocity correction

... Orderly arranged rotors, along with the flow velocity distribution, are displayed in Figure 13. The configuration was reported in [42], and the numerical work was performed in the present study to describe flow parameter distributions. From a global view, the near-rotor flow patterns are analogous for the three rotors. ...

Applications of the Savonius rotor have been extended in recent years, necessitating an in-depth investigation on flow characteristics of such a fluid energy converting device. For the wake flow downstream of the Savonius rotor, studies have been reported extensively. Nevertheless, literature specifically devoted to the upstream flow of the Savonius rotor can rarely be found. This review collects and compiles findings from relevant studies to prove the significance of upstream flow patterns to the operation of the Savonius rotor. Then attempts from experimental and numerical aspects to substantiate the important effect of the upstream flow are implemented. Based on practical cases and laboratory works, upstream flow patterns for the Savonius rotor are divided into four types, namely uniform flow, guided flow, rotor wake flow and oscillating flow. Accordingly, conditions under which these upstream flow patterns arise are analyzed respectively. Experimental and numerical results are presented to clarify the influential factors underlying diverse upstream flow patterns. Furthermore, the relationship between the performance of the Savonius and the upstream flow is elucidated, facilitating the development of techniques of controlling the upstream flow. This review provides a systematic reference for the control of the upstream flow for the Savonius rotor, which has the tendency of developing into an independent technical branch.

... Later Muller et al. used it for flat plate shaped wind blade [13]. The most recent approach to VAWT related with the number of blades was made by [17] and further research to improve the drag wind turbine performance was done by [18]. ...

Technology of wind exploitation has been applied widely all over the world and has already reached the level in which manufacturers want to maximize the yield with the minimum investment outlays. The main objective of this paper is the determination of the optimal number of blades in the Cup-Bladed Vertical Axis Wind Turbine. Optimizing the size of the Vertical Axis Wind Turbine allow the reduction of costs and increase the output. The target is the maximum power of the rotor. The optimum number of Vertical Axis Wind Turbine blades evaluation is based on analysis of a single blade simulation and its superposition for the whole rotor. The simulation of working blade was done in MatLab environment. Power spectrum graphs were prepared and compared throughout superposition of individual blades in the Vertical Axis Wind Turbine rotor. Some wind tunnel measurements of the hydrodynamic force according to pitch angle of the blade are also shown. The major result of this research is the Vertical Axis Wind Turbine kmax ratio power characteristic. On the basis of the analysis of the power spectra, optimum number of the blades was specified for the analysed rotor. Power spectrum analysis of wind turbine enabled the specification of the optimal number of blades, and can be used regarding investment outlays and power output of the Vertical Axis Wind Turbine.

... Bu arada, rotor tasarımı araştırmalarında ise El-Baz vd. [17] yeni bir tasarım olarak üçgen bir modele göre yapılan üç-rotorlu Savonius tipi türbin geliştirdiklerini yayımlamışlardır. Bu yeni tasarımın tek rotora sahip tasarımlardan daha yüksek güç katsayılarına sahip oldukları sunulmuştur. ...

In this paper, Stochastic Frontier Analysis (SFA) technique is contributed to measure the productive efficiency of a working wind farm. In the current literature SFA, which is one of the commonly used efficiency analysis tool in many different areas, has not been studied previously to measure wind turbine efficiencies. Stochastic nature is the key advantage of SFA, whereby frontier deviations include both external effects that are not within the company's control and technical inefficiency. The proposed approach was used to calculate efficiency of each wind turbines to compare each other and to determine whole wind farm efficiency according to four different cases. These cases were introduced to determine the effects of different input parameters on the efficiency levels. Thereby, the other crucial interest of this study is to answer which factors are effective to measure the efficiency of a wind turbine by implementing four different input oriented cases. Also, these four cases studied under three different time periods; monthly averaged data, twelve monthly averaged data, and twenty four monthly data. Results showed that different input groups gave different efficiency results. Whether the efficiency loses originated from statistical noise or technical inefficiency could be concluded by the advantage of SFA.

... Bu arada, rotor tasarımı araştırmalarında ise El-Baz vd. [17] yeni bir tasarım olarak üçgen bir modele göre yapılan üç-rotorlu Savonius tipi türbin geliştirdiklerini yayımlamışlardır. Bu yeni tasarımın tek rotora sahip tasarımlardan daha yüksek güç katsayılarına sahip oldukları sunulmuştur. ...

... The most recent approach to VAWT related with the number of blades was made by [16] and further research to improve the drag wind turbine performance was done by [17]. ...

Technology of wind exploitation has been applied widely all over the world and has already reached the level in which manufacturers want to maximize the yield with the minimum investment outlays. The main objective of this paper is the determination of the optimal number of blades in the Cup-Bladed Vertical Axis Wind Turbine. Optimizing the size of the Vertical Axis Wind Turbine allows the reduction of costs. The maximum power of the rotor is selected as the performance target. The optimum number of Vertical Axis Wind Turbine blades evaluation is based on analysis of a single blade simulation and its superposition for the whole rotor. The simulation of working blade was done in MatLab environment. Power spectrum graphs were prepared and compared throughout superposition of individual blades in the Vertical Axis Wind Turbine rotor. The major result of this research is the Vertical Axis Wind Turbine power characteristic. On the basis of the analysis of the power spectra, optimum number of the blades was specified for the analysed rotor. Power spectrum analysis of wind turbine enabled the specification of the optimal number of blades, and can be used regarding investment outlays and power output of the Vertical Axis Wind Turbine.

... The modern windmills have been furnished with turbines that create a kinetic energy which is then converted to electricity. In an effort to improve the efficiency of wind power generation, various technologies have been tested with an aim of increasing efficiencies of wind power such as flat detector [5], three-rotor savonious [6], fixed pitch angle variation [7], number blades in savonious [8]. Another method employs the wind lens technology which is by far going to increase the generation of wind power energy [9]- [12]. ...

... Mohammed et al. [21] analyzed a cluster with two and three turbines, varying several factors such as inter-axial distance, wind incidence angle and rotation direction of the turbines. Generally, data present in literature are related to clusters composed of two or at most three turbines (El-Baz et al. [22]), arranged in different configurations. ...

This work focuses on Savonius turbine numerical modeling and mutual turbine interaction in a linear array farm. Two-dimensional Computational Fluid Dynamics modeling was carried out using the open source solver OpenFOAM. Results are compared with available experimental data and three-dimensional CFD modeling. The influence of main parameters, such as the distance between adjacent turbines, the wind incidence angle and the number of turbines is investigated and the linear array efficiency is defined. The obtained results show a performance increase as the distance between the turbines reduces, higher efficiency for small wind incidence angles, and a larger number of turbines.

... The modern windmills have been furnished with turbines that create a kinetic energy which is then converted to electricity. In an effort to improve the efficiency of wind power generation, various technologies have been tested with an aim of increasing efficiencies of wind power such as flat detector [5], three-rotor savonious [6], fixed pitch angle variation [7], number blades in savonious [8]. Another method employs the wind lens technology which is by far going to increase the generation of wind power energy [9]- [12]. ...

The main objective of this research is to investigate the effect of attaching nozzle lens with difference diameter and number of blades in non-twisted NACA 4415 on the power output of the Horizontal Axis Wind Turbine (HAWT). The Artificial of low wind speed were used in this experiment at 2.5 m/s, 3.5 m/s, and 4.5 m/s. The result shows that the lenses increase the power output. The lens diameter is directly proportional to the rotor speed and TSR of the turbine. In the difference number of blades, the three-blades turbine consistently generates the highest power output compared to two-blades and four-blades turbines. The evidence has established that nozzle lenses and three-blades turbine can successfully increase the efficiency of wind turbines in areas where wind speed is low.

... Shih and et al. [10] showed that, the normal stress can't be negative and Schwartz inequality ( ́ ́ ̅̅̅̅̅̅ 1 is satisfied. The Realizable model usually provides improvement results for swirling flow and flow involved separation compared to other models [11]. This model has been proclaimed to yield of good agreement with the experimental measurements on the flow field of Savonius turbine by Mohamed and et, al. [12]. ...

... Hence, different configurations were explored using CFD techniques to improve efficiency. El-Baz et al. 3 , showed that the peak power coefficient of a novel Savonius design achieved 44% higher performance than that of the ordinary rotor. Another design, developed by El-Askary et al. 4 , reached a power coefficient peak of 0.52. ...

The Savonius vertical axis wind turbine is a simple device, easy to manufacture, has good starting characteristics, and rotates with wind from any direction; nevertheless, it has a lower efficiency than the other wind turbines. The aim of this paper is to numerically explore the non-linear unsteady flow over a conventional Savonius using three dimensional computations with emphasis on the placement of these turbines in a linear array and the effect of an obstacle that acts as a wind deflector. First, an infinite array of turbines is used to study the gap distance between the wind turbine axis rotors. This investigation is conducted via numerical simulations based on the computational fluid dynamics computer program Fluent 14.5. It is found that a gap distance L = 1.4R gives a very good performance. Second, four farms with different number of turbines - from 3 to 21 turbines - are studied. The effect on the power coefficient of the number of turbines in each farm is reported and analyzed. Third, a new arrangement that includes an obstacle at one end of the array of turbines is presented. The best configuration explored in this work increases the power coefficient of each Savonius wind turbine by 82% compared to a single turbine. Finally, the effect of the wind direction for the best configuration is presented and the range of wind angles for which the farm outperforms isolated turbines is calculated.

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In this study, the turbine performances of Savonius wind turbines were investigated in the case of dual usage. While implementing the dual use of the Savonius wind turbine, a flat plate deflector was placed in front of the turbines to increase the turbine performance. The effects of design parameters such as the geometric dimensions of this flat plate placed in front of the turbines and the geometrical placement position on the turbine performance were investigated. In this direction, the flat plate prevented the negative torque that occurs during the operation of the turbines. Hence, the plate guided the wind to the turbine blade, which generated positive torque. The numerical analyses made in this study were confirmed by the previous literature study. The performance values of single, dual, and flat plate dual Savonius wind turbines were analyzed using the numerical analysis method, the accuracy of which was proven by the experimental data. It was determined that the similarity between the experimental result and the numerical result was approximately 0.3%, especially in the maximum power coefficient values. The computational fluid dynamics (CFD) program ANSYS Fluent was used for turbine performance analysis. With this design study, the maximum power coefficient ( C p ) was obtained around 0.17 with a single Savonius wind turbine, while the maximum power coefficient ( C p ) was obtained around 0.24 with a flat plate dual Savonius wind turbine. As a result, the power coefficient obtained with a single Savonius wind turbine increased by 42% in the flat plate dual Savonius turbine system when compared to the power coefficient of the single Savonius wind turbine. Thus, it was determined that the power coefficient obtained with a single Savonius wind turbine in the flat plate dual Savonius turbine system increased by 42% compared to the power coefficient of the single Savonius wind turbine.

Savonius wind turbines are low-efficiency drag-driven turbines, however an efficient clustering of Savonius turbines in close proximity boosts positive coupling among the turbines. The primary goal of this research is to analyze the flow-driven characterization of Savonius wind turbine clusters using a modified wind turbine in order to forecast the positive couple effect and enhanced power coefficient. The 2D numerical study is modeled using open source CFD toolbox OpenFOAM-v1812 with unsteady RANS solver overPimpleDyMFoam adopting dynamic overset mesh approach. For a two turbine configuration, the wind-driven positive interaction is determined by accounting the effective separation distance with linear and oblique arrangement, as well as with varied rotation direction (Co-rotating and Counter-rotating turbines). The modified two turbine oblique and linear clusters display an overall torque coefficient Ct of 20.18% and 17.04% higher than the single turbine study.

Many countries are currently making the transition from CAD modeling to BIM modeling and project management. There are considerable challenges for a society to integrate these new methodologies in an industry that is so changing, where many professional disciplines are involved, and whose economic contribution is relevant for the growth of a nation. There are different authors in the global context that have documented the advantages in the implementation of the methodology, but this does not mean that it is a simple process. In this sense, the undergraduate programs of universities play a fundamental role. This document describes the exercise that was done, on the recognition of the process that would be required to achieve the implementation of the BIM methodology in the current Civil Engineering program of the Catholic University of Colombia, in this, it reflects on the most relevant aspects to consider in the approach of BIM from the academy, particularly from Engineering.

Savonius turbines for wind and hydrokinetic applications both operate on the same principle in terms of power generation. However, the effects of their power performance when augmented with various deflector configurations in wind and water have not been comprehensively investigated, and the comparative analysis in the literature still lacks due to the different fluid mediums. Therefore, the present study aims to evaluate and compare the power performance of a conventional Savonius turbine augmented with various deflector longitudinal positions, heights, and angles using a water channel and a wind tunnel with identical flow dynamics. The same turbine model and deflector configurations were tested at equivalent flow rates with the same Reynolds number of 1.48 × 10⁵, corresponding to a typical flow condition in hydrokinetic applications. The turbine power performance, when operated in the wind tunnel, was found to match relatively well with the corrected results of the turbine power performance operated in the water channel, despite being tested in different fluid mediums. In addition, the trends for maximum coefficients of power for both tests are similar in terms of the variations of the deflector angles and the longitudinal positions, resulting in the same deflector parameters that contributed to the best power performance. The maximum coefficient of power, its corresponding coefficient of torque, and tip speed ratio obtained in the wind tunnel differ from the water channel results by 3.98%, 4.44%, and -1.08%, respectively. As a result, this study validates wind tunnel measurements of the power performance of Savonius turbines for hydrokinetic applications, augmented with flow deflectors. Therefore, results obtained in wind tunnel experiments can be used to evaluate the turbine power performance for hydrokinetic applications provided that the principle of flow similarity between the two mediums, wind and water, is satisfied.

Wind power is sustainable and prevalent virtually all over the globe. However, the conversion efficiency of the conventional single-rotor wind turbine (SRWT) is still far from satisfactory. The dual-rotor counter-rotating concept is among the reliable techniques used to enhance the efficiency of a wind energy conversion device for its renowned effectiveness. This study aims to investigate the performance of a Savonius dual/twin-rotor system, particularly in low-speed wind conditions while employing the counter-rotating technique. The evaluation of this technique is presented in terms of aerodynamic characteristics, including the power and torque coefficients. The results have shown that the new concept was able to improve the performance of the system extensively and was
capable of operating in a lower wind speed condition. Compared to a single-rotor system, an additional 42% more torque was possible owing to the existence of a second rotor in the new system. The results have also revealed that the conversion efficiency of the system has been enhanced substantially. A corresponding average power coefficient of up to 28% was achieved. The present technique is thought to be promising for wind energy conversion systems, including sites with poor wind conditions.

The effects of adding inner blades to the Bach-type Savonius turbine deserve extensive attention due to its promising improvement of the performance over the conventional turbine. In the present work, the performance improvement is based on comparing the power coefficient of two modified configurations, which produced by installing concentric blade inside the original rotor blade of the conventional Savonius rotor. Numerical simulations are performed for three configurations: the traditional rotor; turbine with the additional inner blades tip parallel to the original turbine blades tip; and turbine with the additional inner blades parallel to the original rotor blades root. Numerical CFD analysis is carried out to study the influence of varying the radius and/or the central angles of the additional inner blades applying ANSYS FLUENT. The considered radius of the additional blades ranges from 0.25 to 0.85 of that of the reference blade whereas the blade central angle varied from 70° to 180°. The acquired numerical results reveal that the performance of the turbine with additional inner blades is increased by 22.39%, 46.27%, and 103.86% when the tip speed ratio equals 0.75, 0.25, and 1.3, respectively.

Nile River is considered as an auspicious area; in particular along with Upper Egypt, to produce electrical energy from the water current which called hydrokinetic energy. This sort of renewable energy is admitted deeply as a unique and uncommon solution for the electric power demand in the remote areas on the rivers' sides. The hydrokinetic energy of the river stream can be extracted by a submerged vertical axis turbine due to its specific advantages. The main objective of this work is to investigate experimentally the performance of two different Savonius rotor profiles inside an irrigation canal in Toshka, Aswan, Egypt. Furthermore, the rotor with the optimum performance is investigated numerically by adding two shielding plates to further enhancements. The results indicate that the rotor with better fullness has better operating characteristics with a power coefficient 0.1285 at a tip speed ratio of 0.61 that is higher than the other rotor profile by 12%. Moreover, the two shielding plates increased the net average power coefficient at a tip speed ratio at 0.7 for the optimum rotor profile by 84% compared with the conventional design.

There are many types of wind turbine. Large propeller-type wind turbines are used mainly for large wind farms and offshore wind power generation. Small vertical-axis wind turbines (VAWTs) are often used in distributed energy systems. In previous studies on wind turbines, the basic characteristics such as torque coefficient have often been obtained during rotation, with the turbine rotating at a constant speed. Such studies are necessary for the proper design of wind turbines. However, it is also necessary to conduct research under conditions in which the wind direction and wind speed change over time. Numerical simulation of the starting characteristics is carried out in this study. Based on the flow field around the wind turbine, the force required to rotate the turbine is calculated. The force used to stop the turbine is modeled based on friction in relation to the bearing. Equations for the motion of the turbine are solved by their use as external force. Wind turbine operation from the stationary state to the start of rotation is simulated. Five parameters, namely, blade length, wind turbine radius, overlap, gap, and blade thickness, are changed and the optimum shape is obtained. The simulation results tend to qualitatively agree with the experimental results for steadily rotating wind turbines in terms of two aspects: (1) the optimal shape has an 20% overlap of the turbine radius, and (2) the larger the gap, the lower the efficiency.

The increasing need for access to reliable off-grid electricity in remote areas, coupled with the negative effects of diesel-based generators, is driving demand for renewable and sustainable energy productions. River-based hydrokinetic turbines are one such environmentally friendly technology that has received growing interest for further scientific studies and real engineering applications within the last decade. Several challenges remain which have hindered the realization of this technology in those areas. This review article focuses on the vertical-axis Savonius hydrokinetic turbines, which are primarily preferred for being simple, practical, and economical for low-load applications in low-income communities in remote areas. The principles, technicalities, and recent improvements of these turbines are comprehensively reviewed and discussed. The potential advantages of implementing such a technology in Malaysia are abundant, primarily due to its monsoon climate with ample precipitation and vast river networks. However, several challenges and gaps still remain, which are identified in this article to further improve the technology for realistic implementation.

In this paper, using numerical simulation, the effects of inward and outward overlaps on the performance of a conventional two-blade Savonius wind turbine and the complete analysis of the events caused by the rotation of the blades have been investigated. Computations have been carried out at several nondimensional overlap ratios such as G/d = 0, ±0.1, ±0.2, and ±0.3 for three wind speeds of 3, 5, and 7 m/s. On the other hand, in the present study, the values of the tip speed ratio (TSR) are considered in the range from 0.2 to 1.2. The obtained results are validated against the available data in the open literature and found excellent agreements between them. Several results such as the instantaneous velocity and pressure fields in the rotating zone, variation of torque coefficients in one complete cycle of the rotor, and mean power coefficient distributions as a function of TSR and wind speed have been presented in this numerical investigation. The results show that, regardless of the overlap ratio, the maximum power coefficient occurs at a tip speed ratio (TSR) of 0.8. Additionally, the maximum power coefficient is observed in the inwards overlap ratio of 0.2 and an increasing or decreasing the overlap ratio reduces the maximum value of the power coefficient in all wind speeds under consideration. Finally, it was concluded that at each TSR and G/D value, increasing the wind speed enhances the power coefficient of two-blade Savonius VAWT. It was hoped the obtained results arouse interest among the VAWT designers.

For an in-line arrangement of two drag-type hydrokinetic rotors, flow patterns between the two rotors and the rotor performance were investigated. The flows were measured using time-resolved particle image velocimetry (TR-PIV) technique. Computational fluid dynamics (CFD) technique was used to quantify the rotor performance. Emphasis was placed upon the influence of the rotor angle and the inter-rotor distance. The results show that two large-scale vortices dominate the wake of the upstream rotor. Expanding, shrinking and shifting of the large-scale vortices significantly influence the rotor performance. Three distinct regions, velocity-rising, velocity declining and velocity-recovery regions, are defined. They serve as indicators of the impact of the downstream rotor on the upstream rotor. Instantaneous wake flow patterns between the two rotors alter with the orientation of the two rotors. The most adverse effect on the upstream rotor arises as the upstream rotor area that faces the incident flow reaches its maximum. At high upstream velocity, both the torque output and the power coefficient of the upstream rotor approach their counterparts associated with the single rotor. With increasing inter-rotor distance, the negative impact of the downstream rotor on the upstream rotor decays continuously. An inter-rotor distance larger than five times the rotor diameter is suggested.

This work presents an innovative technique to enhance the performance of the Savonius wind turbine. The new technique is based on introducing an upstream deflector and downstream baffle. The shape and location of both devices are optimized using a genetic algorithm. The performance of the turbine with the optimized devices is compared with the single Savonius turbine performance. The study employs the finite volume solver (ANSYS-FLUENT) to solve unsteady Reynolds Averaged Navier–Stokes equations and turbulence model equations. The optimized configuration results in much higher power coefficient than the Savonius turbine. The average peak power coefficient using both deflector and baffle is 0.47 compared to 0.24 of the Savonius turbine. The peak power coefficient of the turbine corresponds to a speed ratio close to unity. This improved performance is attributed to the favorable aerodynamic interaction between the turbine and the downstream baffle which accelerates the flow around the rotor and generates larger turning torque. The baffle generates a jet effect on the advancing bucket and accelerates the flow behind the bucket creating a large zone of negative pressure and thereby increases the driving torque. Furthermore, the upstream deflector (also called shield or curtain) produces a shield for the returning bucket of the turbine which diminishes the adverse effect associated with the returning bucket on the aerodynamic torque of the turbine. This remarkable improvement of turbine performance will encourage the future application of the Savonius wind turbine in small power applications of wind energy.

Modeling and performance study of large parabolic trough solar power plant using molten slat storage tank is conducted and presented for three different locations in Egypt (Aswan, Al-Arish and Hurghada) using 16 h storage system. The simulation algorithm and solar modeling have been created and simulated by MATLAB/SIMULINK program. A comparison between studied cities is introduced to select the best location for constructing the solar plant based on selection criteria; hot header outlet temperature, volume (hot and cold) variations during charging and discharging, and cycle power efficiency. A full design of the thermal power plant with the storage tanks is also conducted using a molten salt (60% NaNO3 and 40% KNO3). Moreover, hourly electricity plant output to obtain the influence of the thermal storage tank on the plant performance was calculated and presented. The results indicated that Aswan city is the optimum location to construct a 500 MW solar power plant under the Egyptian climate. A comparison for current model validation between simulated results and the actual results of existing plant (Archimede) was fulfilled and good agreement was obtained by maximum error 5%.

In this study, we present the results of a two-dimensional fluid-dynamic simulation of novel rotor geometry with spline function which is derivative of the traditional S-shape Savonius blade. A computational fluid dynamic (CFD) analysis is conducted using the Spalart-Allmaras turbulent model, validated using experimental data released by Sandia National Laboratory. Results are presented in terms of dimensionless torque and power coefficients, assuming a wind speed of 7 m/s and height and rotor diameter of 1m. Furthermore, analysis of the forces acting on the rotor is conducted by evaluating frontal and side forces on each blade, and the resultant force acting on the central shaft. A qualitative representation of the vorticity around the traditional and spline rotor is shown to prove that the novel blade allows less turbulent flow through the rotor.

Wind energy represents a very important source of energy for many countries nowadays. Wind energy provides an efficient and an effective solution to reduce fusel fuel consumption as well as pollutant emissions. VAWTs (vertical axis wind turbines) were originally considered as very promising, before being subrogated by the present, horizontal axis turbines. There is now a resurgence of interests for VAWTs, in particular Darrieus turbines. VAWTs (vertical axis wind turbines) like the Darrieus turbine appear to be particularly promising for the conditions of low wind speed, but suffer from a low efficiency compared to horizontal axis turbines. Additionally, VAWTs are not always self-starting, which is a major drawback. The present paper introduces the main problem of the self-stating capability of Darrieus turbine and investigates some techniques to improve this drawback. The effect of the turbine solidity and the usage of hybrid system between drag and lift types have been investigated in this paper numerically using CFD (Computational Fluid Dynamics) technique and experimentally. A considerable improvement of the H-rotor Darrieus turbine self-starting capability can be obtained by these techniques. (c) 2013 Elsevier Ltd. All rights reserved.

The problems aided with wind turbine noise have been one of the more studied environmental influence areas in wind energy engineering. Noise levels can be measured, but, similar to other environmental attentions, the public's perception of the noise impact of wind turbines is in part a subjective determination. The author investigated in this work the aerodynamic acoustics of one type of the VAWT (vertical axis wind turbine) which called Darrieus turbine. Darrieus turbine is suitable to be established within the densely populated city area. Therefore, the noise item is very important to investigate. In this work, Darrieus rotor has been studied numerically and aerodynamically to obtain the generated noise from blades. This work offers a method based on the FW-H (Ffowcs Williams and Hawkings) equations and its integral solutions. Time-accurate solutions can be obtained from URANS (unsteady Reynolds-averaged Navier Stokes) equations. Blade shape, tip speed ratio and solidity effects have been studied in this work. The results indicated that the higher solidity and higher tip speed ratio rotors are more noisy than the normal turbines.

The Savonius rotor is a slow running vertical axis wind turbine, the advantages of which are numerous ; however, it has a poor aerodynamic efficiency. We present a study aiming to raise this efficiency by adjusting several geometrical parameters, in particular the overlap of the paddles and their respective position. The results are coming from a bidimensional numerical simulation, using the CFD code Fluent v6.0. First the numerical model is validated on the conventional Savonius rotor. Then the geometry of an optimised Savonius rotor is proposed, the overlap ratio of which is 0.242. Last a different positioning of the paddles leads to an optimal paddle angle of about 55°, corresponding to the maximum of the mean starting torque coefficient.

A Savonius rotor can be used as a wind or water current energy conversion device that produces electricity. In spite of their simple structure and assembly, Savonius turbines have less commercial appeal than other types of turbines due to their relatively low energy conversion efficiency. In order to increase the output power of a Savonius turbine, most studies have only focused on optimization of the rotor configuration or installation of ancillary equipment around the rotor. However, previous research has found that a beneficial interaction that existed between two parallel Savonius turbines can also augment the power output of each rotor if they are rotating side by side. This paper numerically examines the interactions among multiple Savonius turbines with the help of the commercial computational fluid dynamics software fluent and finds that these coupling effects can effectively increase the overall power output of a Savonius turbine farm, especially when Savonius turbines are arranged relatively close together. Numerical results also indicate that the separation distance and relative phase angle between the two adjacent Savonius rotors can greatly influence this positive interaction between them.

This paper aims to present the study of flow through a vertical axis wind turbine of Savonius type. The studied turbine is intended to be used within a compact package with multisource of energy. The rotor has height, which is approximately equivalent to the rotor diameter. In this condition, the simulation of flow through the wind turbine needs 3D model. Due to its principle of operation and the continuous variation of flow angle with respect to blades, strong unsteady effects including separation and vortex shedding are observed. In these conditions, the turbulence modeling by means of k-ω and DES permits to obtain good results comparatively to experiments. In this work we are using CFD to study the behaviour of a Savonius wind turbine under flow field conditions and to determine its performance and the evolution of wake geometry. The flow analysis helps to qualify the design of the wind turbine. To validate simulations, experimental investigation in wind tunnel is carried out using PIV. The investigation permits to determine the structure of the real flow and to access the quality of numerical simulations

The Savonius rotor is a slow running vertical axis wind turbine, the advantages of which are numerous ; however, it has a poor aerodynamic efficiency and a very unsteady mechanical torque. We present the results of numerical simulations of the flow around derived Savonius rotors, aiming to raise and stabilise the torque. It is the reason why several geometrical parameters have been adjusted, in particular the overlap of the paddles and their respective position. Then a rotor with displaced blades is studied. The results obtained on few configurations of rotors show that the two-bladed rotor, called reverse paddles rotor, seems to be the most efficient.

This paper discusses the influence of the buckets overlap ratio of a Savonius wind rotor on the averaged moment and power coefficients, over complete cycles of operation. The continuity and Reynolds Averaged Navier-Stokes (RANS) equations, and the Eddy Viscosity Model k-omega, SST, on its Low-Reynolds approaches, using hybrid near wall treatment; are numerically solved by the commercial software Star-CCM(+). This software is based on Finite Volume Method and computes the pressure and velocity fields of the flow and the forces acting on the rotor buckets. The moment and power coefficients are achieved by integrating the forces coming from the effects of pressure and viscosity of the wind on the device. The influence of the buckets overlap ratio on the moment and power coefficients is checked by changing the geometry of the rotor, keeping the Reynolds number, based on rotor diameter, equal to 433,500. The results obtained for the rotor with zero overlap are in agreement with those obtained experimentally by other authors what indicates that the method can be successfully used for such analysis. The values of the moment and power coefficients obtained as a function of tip speed ratio and the buckets overlap of the rotor indicates that the maximum device performance occurs for buckets overlap ratios with values close to 0.15.

This work has resulted in the publications of a monograph that summarises the performance areodynamics of a variety of wind actuated, power producing machines. Several areas important to wind power production were identified in which adequate aerodynamics models have not been developed. Under NSF/RANN Grant AER 74-04014 A03 the following topics will be studied: (i) aerodynamics of the Darrieus rotor; (ii) performance and configuration of the optimum horizontal axis rotor; (iii) aerodynamics of low-tip-speed, high-solidity horizontal axis rotors; (iv) aerodynamics of the Savonius rotor. In all these areas, some groundwork for the development of aerodynamic performance models has already been accomplished. (from paper)

This paper presents a review on the performance of Savonius wind turbines. This type of turbine is unusual and its application for obtaining useful energy from air stream is an alternative to the use of conventional wind turbines. Simple construction, high start up and full operation moment, wind acceptance from any direction, low noise and angular velocity in operation, reducing wear on moving parts, are some advantages of using this type of machine. Over the years, numerous adaptations for this device were proposed. The variety of possible configurations of the rotor is another advantage in using such machine. Each different arrangement of Savonius rotor affects its performance. Savonius rotor performance is affected by operational conditions, geometric and air flow parameters. The range of reported values for maximum averaged power coefficient includes values around 0.05–0.30 for most settings. Performance gains of up to 50% for tip speed ratio of maximum averaged power coefficient are also reported with the use of stators. Present article aims to gather relevant information about Savonius turbines, bringing a discussion about their performance. It is intended to provide useful knowledge for future studies.

Since millenaries humans have attempted to harness the wind energy through diverse means. Vertical axis wind turbines (VAWTs) were originally considered as very promising, before being superseded by the present, horizontal axis turbines. For various reasons, there is now a resurgence of interests for VAWTs, in particular Darrieus turbines. Using modern design tools and computational approaches, it should be possible to increase considerably the performance of traditional VAWTs, reaching a level almost comparable to that of horizontal axis turbines. Since VAWTs show many specific advantages (compact design, easier connection to gears/generator, easier blade control if needed, lower fatigue…), it is important to check quantitatively the efficiency of such turbines. This is the purpose of the present work, starting from the standard, straight Darrieus turbine (H-rotor). The aerodynamic investigation will be carried out for 20 different airfoils (Symmetric and Non-symmetric) by two-dimensional Computational Fluid Dynamics in order to maximize output torque coefficient and output power coefficient (efficiency). A considerable improvement of the H-rotor Darrieus turbine performance can be obtained in this manner.

In this study, a curtain design has been arranged so as to improve the low performance levels of the Savonius wind rotors. Designed to prevent the negative torque on the convex blade of the rotor, this curtain has been placed in front of the rotor, and performance experiments have been carried out when the rotor is with and without curtain. It has been determined from here that a significant increase can be achieved in the rotor performance by means of the curtain design. Experiments of the curtain design have been conducted in three different dimensions when the Savonius wind rotor is static, and the highest values have been obtained with the curtain 1. Therefore, the curtain designs and curtain angles in which the highest values obtained have been analyzed numerically with Fluent 6.0 program and the results obtained experimentally have been supported with numerical analysis. Moreover, performance experiments have been made for the curtain 1 with which the best performance values have been obtained when the rotor is in its dynamic position, and the results obtained have been given in figures.

This paper presents a study, carried out with the help of the French Agency of Innovation (ANVAR). It deals with the conception of a small Savonius rotor (i.e. of low power) for local production of electricity. Our challenge was to design, develop and ultimately build a prototype of such a rotor, which was considered as a complete electromechanical system. An optimised configuration was chosen for the geometry of the present prototype. The building data were calculated on the basis of the nominal wind velocity V=10 m/s. Particular care was necessary to choose the appropriate generator, which was finally a rewound conventional car alternator. The whole design of the prototype has confirmed the high efficiency and the low technicality of the Savonius rotors for local production of electricity. The present prototype is to be tested in situ.

When compared with of other wind turbine the Savonius wind rotor offers lower performance in terms of power coefficient, on the other hand it offers a number of advantages as it is extremely simple to built, it is self-starting and it has no need to be oriented in the wind direction. Although it is well suited to be integrated in urban environment as mini or micro wind turbine it is inappropriate when high power is requested. For this reason several studies have been carried-out in recent years in order to improve its aerodynamic performance. The aim of this research is to gain an insight into the complex flow field developing around a Savonius wind rotor and to evaluate its performance. A mathematical model of the interaction between the flow field and the rotor blades was developed and validated by comparing its results with data obtained at Environmental Wind Tunnel (EWT) laboratory of the “Polytechnic University of Marche”.

Fifteen configurations of a Savonius rotor wind turbine were tested in the Vought Corporation Systems Division 4.9- x 6.1-m Low Speed Wind Tunnel to determine aerodynamic performance. The range of values of the varied parameters was as follows: number of buckets, 2 and 3; nominal freestream velocity, 7 and 14 m/s; Reynolds number per meter, 4.32 x 10/sup 5/ and 8.67 x 10/sup 5/; rotor height, 1 and 1.5 m; rotor diameter (nominal), 1 m; bucket overlap, 0.0 to 0.1 m. The measured test variables were torque, rotational speed, and tunnel conditions. It is concluded that increasing Reynolds number and/or aspect ratio improves performance. The recommended configuration consists of two sets of two-bucket rotors, rotated 90 deg apart, with each rotor having a dimensionless gap width of 0.1 to 0.15.

Due to the worldwide energy crisis, research and development activities in the field of renewable energy have been considerably increased in many countries. Wind energy is becoming particularly important. Although considerable progress have already been achieved, the available technical design is not yet adequate to develop reliable wind energy converters for conditions corresponding to low wind speeds and urban areas. The Savonius turbine appears to be particularly promising for such conditions, but suffers from a poor efficiency. The present study considers a considerably improved design in order to increase the output power of a classical Savonius turbine. In previous works, the efficiency of the classical Savonius turbine has been increased by placing in an optimal manner an obstacle plate shielding the returning blade. The present study now aims at improving further the output power of the Savonius turbine as well as the static torque, which measures the self-starting capability of the turbine. In order to achieve both objectives, the geometry of the blade shape (skeleton line) is now optimized in presence of the obstacle plate. Six free parameters are considered in this optimization process, realized by coupling an in-house optimization library (OPAL, relying in the present case on Evolutionary Algorithms) with an industrial flow simulation code (ANSYS-Fluent). The target function is the output power coefficient. Compared to a standard Savonius turbine, a relative increase of the power output coefficient by almost 40% is finally obtained at λ = 0.7. The performance increase exceeds 30% throughout the useful operating range. Finally, the static torque is investigated and found to be positive at any angle, high enough to obtain self-starting conditions.

Due to the worldwide energy crisis, research and development activities in the field of renewable energy have been considerably increased in many countries. In Germany, wind energy is becoming particularly important. Although considerable progress has already been achieved, the available technical design is not yet adequate to develop reliable wind energy converters for conditions corresponding to low wind speeds and urban areas. The Savonius turbine appears to be particularly promising for such conditions, but suffers from a poor efficiency. The present study considers a considerably improved design in order to increase the output power of a Savonius turbine with either two or three blades. In addition, the improved design leads to a better self-starting capability. To achieve these objectives, the position of an obstacle shielding the returning blade of the Savonius turbine and possibly leading to a better flow orientation toward the advancing blade is optimized. This automatic optimization is carried out by coupling an in-house optimization library (OPAL) with an industrial flow simulation code (ANSYS-Fluent). The optimization process takes into account the output power coefficient as target function, considers the position and the angle of the shield as optimization parameters, and relies on Evolutionary Algorithms. A considerable improvement of the performance of Savonius turbines can be obtained in this manner, in particular a relative increase of the power output coefficient by more than 27%. It is furthermore demonstrated that the optimized configuration involving a two-blade rotor is better than the three-blade design.

The use of a Savonius type of vertical axis wind turbine is expanding in urban environments as a result of its ability to withstand turbulence as well as its relatively quiet operation. In the past, single turbine performance has been investigated primarily for determining the optimum blade configuration. In contrast, combining multiple Savonius turbines in the horizontal plane produces extra power in particular configurations. This results from the interaction between the two flow fields around individual turbines. To understand quantitatively the interaction mechanism, we measured the flow field around two Savonius turbines in close configurations using particle image velocimetry. The phase-averaged flow fields with respect to the rotation angle of the turbines revealed two types of power-improvement interactions. One comes from the Magnus effect that bends the main stream behind the turbine to provide additional rotation of the downstream turbine. The other is obtained from the periodic coupling of local flow between the two turbines, which is associated with vortex shedding and cyclic pressure fluctuations. Use of this knowledge will assist the design of packaged installations of multiple Savonius turbines.

A new k-[epsilon] eddy viscosity model, which consists of a new model dissipation rate equation and a new realizable eddy viscosity formulation, is proposed in this paper. The new model dissipation rate equation is based on the dynamic equation of the mean-square vorticity fluctuation at large turbulent Reynolds number. The new eddy viscosity formulation is based on the realizability constraints; the positivity of normal Reynolds stresses and the Schwarz' inequality for turbulent shear stresses. We find that the present model with a set of unified model coefficients can perform well for a variety of flows. The flows that are examined include: (i) rotating homogeneous shear flows; (ii) boundary-free shear flows including a mixing layer, planar and round jets; (iii) a channel flow, and flat plate boundary layers with and without a pressure gradient; and (iv) backward facing step separated flows. The model predictions are compared with available experimental data. The results from the standard k-[epsilon]

Modern wind farms comprised of horizontal-axis wind turbines (HAWTs) require
significant land resources to separate each wind turbine from the adjacent
turbine wakes. This aerodynamic constraint limits the amount of power that can
be extracted from a given wind farm footprint. The resulting inefficiency of
HAWT farms is currently compensated by using taller wind turbines to access
greater wind resources at high altitudes, but this solution comes at the
expense of higher engineering costs and greater visual, acoustic, radar and
environmental impacts. We investigated the use of counter-rotating
vertical-axis wind turbines (VAWTs) in order to achieve higher power output per
unit land area than existing wind farms consisting of HAWTs. Full-scale field
tests of 10-m tall VAWTs in various counter-rotating configurations were
conducted under natural wind conditions during summer 2010. Whereas modern wind
farms consisting of HAWTs produce 2 to 3 watts of power per square meter of
land area, these field tests indicate that power densities an order of
magnitude greater can potentially be achieved by arranging VAWTs in layouts
that enable them to extract energy from adjacent wakes and from above the wind
farm. Moreover, this improved performance does not require higher individual
wind turbine efficiency, only closer wind turbine spacing and a sufficient
vertical flux of turbulence kinetic energy from the atmospheric surface layer.
The results suggest an alternative approach to wind farming that has the
potential to concurrently reduce the cost, size, and environmental impacts of
wind farms.

Design Optimization of Savonius and Wells Turbines

- M H Mohamed

M.H. Mohamed, Design Optimization of Savonius and Wells Turbines, Ottovon-Guericke University, Magdeburg, 2011.

Pr evision des performances a erodynamiques d'un nouveau type d' eolienne a axe vertical: le rotor a contrevoiles

- J Menet
- N Bourabaa

J. Menet, N. Bourabaa, Pr evision des performances a erodynamiques d'un
nouveau type d' eolienne a axe vertical: le rotor
a contrevoiles, in: 18 e Congr es
Français de M ecanique, 2007. Grenoble.