Influence of varying the stage aspect ratio on the performance of multi-stage Savonius wind rotors

2021 ◽  
pp. 1-18
Author(s):  
Ahmed S. Saad ◽  
Shinichi Ookawara ◽  
Mahmoud Ahmed
Keyword(s):  
Aspect Ratio ◽  
Vertical Axis ◽  
The Self ◽  
Power Coefficient ◽  
Vertical Axis Wind Turbine ◽  
Noise Emission ◽  
Practical Applications ◽  
Operation Conditions ◽  
Aspect Ratios ◽  
Multi Stage

Abstract Although using a multi-stage rotor of Savonius vertical-axis wind turbine enhances the self-starting ability, it reduces the power coefficient. To improve power coefficient, the influence of varying the stage aspect ratio is investigated. Therefore, two-, three-, and four-stage Savonius rotors at stage aspect ratios ranging from 0.5 to 1.5 with increments of 0.25 are considered. To determine performance parameters such as coefficients of torque, power, and thrust, a comprehensive three-dimensional unsteady incompressible turbulent flow model using Reynolds-Averaged Navier-Stokes (RANS) equations along with k-ω shear stress transport turbulence model is developed. The developed numerical model is validated utilizing the available experimental results. Moreover, a novel assessment technique relying on flow field characteristics such as pressure distribution in conjunction with streamlines around the proposed multi-stage Savonius rotor with various stage aspect ratios is carried out. The contribution of each stage on the performance of the whole rotor is computed and presented. The findings of the current study illustrate that utilizing a multi-stage rotor with stage aspect ratio equal to or greater than 1.0 significantly enhances the output power. By rising the stage aspect ratio within the range of 0.5 to 1.5, the peak coefficient of power boosts from 0.163 to 0.213 for a two-stage rotor, and from 0.183 to 0.23 for a four-stage rotor. In addition, three-stage rotors with stage aspect ratio ranging from 0.5 to 1.5, shows increased average static coefficient of torque from 0.196 to 0.272 with positive values at whole rotation angles. This improves the self-starting abilities of the multi-stage rotor and makes it suitable in areas where the wind is intermittent and very low. Furthermore, raising the stage aspect ratio from 0.5 to 1.5 significantly mitigates the oscillations of both torque and thrust coefficients throughout the entire cycle for all multi-stages. This lowers the mechanical vibrations and noise emission during operation conditions. Accordingly, multi-stage Savonius rotors with stage aspect ratio equal to or greater than 1.0 are highly recommended for practical applications.

Experimental Study of Vertical Axis Wind Turbine with Wind Speed Self-Adapting

2012 ◽  
Vol 215-216 ◽  
pp. 1323-1326
Author(s):  
Ming Wei Xu ◽  
Jian Jun Qu ◽  
Han Zhang
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Wind Velocity ◽  
Vertical Axis ◽  
Maximum Power ◽  
The Self ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Opening And Closing

A small vertical axis wind turbine with wind speed self-adapting was designed. The diameter and height of the turbine were both 0.7m. It featured that the blades were composed of movable and fixed blades, and the opening and closing of the movable blades realized the wind speed self-adapting. Aerodynamic performance of this new kind turbine was tested in a simple wind tunnel. Then the self-starting and power coefficient of the turbine were studied. The turbine with load could reliably self-start and operate stably even when the wind velocity was only 3.6 m/s. When the wind velocity was 8 m/s and the load torque was 0.1Nm, the movable blades no longer opened and the wind turbine realized the conversion from drag mode to lift mode. With the increase of wind speed, the maximum power coefficient of the turbine also improves gradually. Under 8 m/s wind speed, the maximum power coefficient of the turbine reaches to 12.26%. The experimental results showed that the new turbine not only improved the self-starting ability of the lift-style turbine, but also had a higher power coefficient in low tip speed ratio.

scholarly journals AIRFOIL SHAPED STRUTS FOR VERTICAL AXIS WIND TURBINE

2021 ◽  
Vol 5 (9) ◽  
Author(s):  
Samyak Jain ◽  
Gautam Singh ◽  
Varun Yadav ◽  
Rahul Bisht
Keyword(s):  
Aspect Ratio ◽  
Wind Energy ◽  
Wind Turbine ◽  
Energy Resource ◽  
Bending Moment ◽  
Clean Energy ◽  
Vertical Axis ◽  
Vertical Axis Wind Turbine ◽  
Aspect Ratios ◽  
Cost Of Energy

Currently, many countries are racing towards switching to clean energy resource (1). Among the options available Solar and Wind are two viable options that are economically feasible. Each day a new development is helping in bringing down the cost of energy extracted from these sources. With currently available technologies, solar energy is almost as expensive as the energy generated from burning coal, whereas wind energy is still slightly expensive (2). However, wind energy could be made cheaper by the use of a vertical axis wind turbine (3). However, structure is a major factor that is holding back the development of VAWTs with better efficiency (4). The efficiency of a VAWT depends upon its aspect ratio. Aspect Ratio is the ratio of the height of the blade to the diameter of the turbine. The lower the aspect ratio, the higher the efficiency (5). However, decreasing the AR would mean either increasing the diameter of the turbine or the height of the blade. In either case, the bending moment would increase on the struts, that connect the blades to the shaft. In this paper we propose, struts with airfoil cross-section. This is because, the lift generated by airfoil struts acts as additional support for the blade, thus increasing our ability to work at lower aspect ratios.

Numerical Modeling of Vertical Axis Wind Turbines

2014 ◽  
Author(s):  
Teresa Parra-Santos ◽  
Armando Gallegos-Muñoz ◽  
Miguel A. Rodriguez-Beneite ◽  
Cristobal Uzarraga-Rodriguez ◽  
Francisco Castro-Ruiz
Keyword(s):  
Mechanical Energy ◽  
Vertical Axis ◽  
The Self ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Tip Speed Ratio ◽  
Vertical Axis Wind Turbines ◽  
Selection Of ◽  
Rotor Axis

This paper aims to predict the performance of Vertical Axis Wind Turbine (VAWT), hence the modeling of kinetic energy extraction from wind and its conversion to mechanical energy at the rotor axis, is carried out. The H-type Darrieus turbine consists of three straight blades with shape of aerofoil attached to a rotating vertical shaft. The criterion on the selection of this kind of turbines, despite its reduced efficiency, is the easy manufacture in workshops. A parametric study has been carried out to analyze the camber effect on the non dimensional curves of power coefficient so that the self starting features as well as the range of tip speed ratio of operation could be predicted.

CFD Sensitivity Analysis of a Straight-Blade Vertical Axis Wind Turbine

2012 ◽  
Vol 36 (5) ◽  
pp. 571-588 ◽  
Author(s):  
Khaled M Almohammadi ◽  
D B Ingham ◽  
L Ma ◽  
M Pourkashanian
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Wind Turbine ◽  
Turbulence Intensity ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Computational Domain ◽  
Vertical Axis Wind Turbine ◽  
Airfoil Surface ◽  
Straight Blade

This paper investigates the flow field features and the predicted power coefficient of a straight blade vertical axis wind turbine (SB-VAWT) using computational fluid dynamics modeling using 2D simulations. The Unsteady Navier-Stokes equations are solved with the concept of Reynolds averaging using the commercial software FLUENT and the sliding mesh technique is applied. In the mesh phase, three parameters have been investigated, namely the cell type, the cell aspect ratio on the airfoil surface, and the total number of cells in the computational domain. In the simulation phase, two parameters have been investigated, namely the time step/Courant number, and the turbulence intensity. Significant differences have been observed in the flow field features and on the predicted power coefficient for some of these parameters which if not considered in details could lead to unreliable predictions. The sensitivity of the parameters is not equally significant and this paper suggests which parameters should be focused on in the modeling process. The convergence behavior of the quadrilateral based mesh is found to be more consistent compared to the triangular based mesh. In the mesh phase, the cell aspect ratio on the airfoil surface was found to be a significant factor, whereas the turbulence intensity was found to be a significant fac-tor in the simulation phase.

Effect of the Number of Stages on the Performance of Savonius Vertical Axis Wind Turbines: Part I — Using Straight Semicircular Blades

2020 ◽  
Author(s):  
Ahmed S. Saad ◽  
Shinichi Ookawara ◽  
Ahmed Elwardany ◽  
Ibrahim I. El-Sharkawy ◽  
Mahmoud Ahmed
Keyword(s):  
Wind Speed ◽  
Phase Shift ◽  
Vertical Axis ◽  
Single Stage ◽  
The Self ◽  
Power Coefficient ◽  
Savonius Rotor ◽  
Multi Stage ◽  
Torque Values ◽  
Two Stages

Abstract The Savonius vertical axis wind turbine offers several benefits as simple construction, low manufacturing, installation and maintenance costs, low operating wind speed, and independence of wind direction. However, the conventional single-stage Savonius rotors have negative torque values at a certain range of rotor angles and large torque variation over the complete cycle which led to reduction of the power coefficient and the self-starting abilities. To overcome these drawbacks, a multi-stage Savonius wind rotor is proposed to obtain the optimum number of stages that enhances both the power coefficient and the self-starting capabilities. In the current study, one-, two-, three-, and four-stage Savonius wind rotors with straight semicircular blades are investigated. In two stages rotor, one single-stage rotor is mounted over another single stage with a phase shift of 90°. In the three stages rotor, the three singlestage rotors are mounted one above the other with a phase shift of 60° relative to one another while with a phase shift of 45° for the four stages. All rotors have overall rotor diameter (D) of 200 mm, a thickness of 2 mm, a stage aspect ratio of 1.0, and an overlap ratio (δ) of 0.0. The diameter of the circular end plates (Do) attached to the rotor tips is 1.1 of the rotor diameter (D). All studies are performed at a wind speed (V) of 6 m/s. The variations of torque and power coefficients are estimated for all the studied multi-stages rotors. Therefore, 3D incompressible unsteady Reynolds-Averaged Navier-Stokes equations along with the k-ω shear-stress transport turbulence model is developed and numerically simulated using ANSYS Fluent. The numerical model is validated using the available measurements and numerical results. The predicted flow field characteristics such as streamlines and pressure fields around the studied rotors with various numbers of stages are presented and analyzed. Accordingly, results indicated that with the increase in the number of stages, a significant enhancement of the torque and the power coefficients is attained. In addition, the rate of percentage gain in the torque and the power coefficients is higher for two stages rotor than that of three and four stages rotors. The maximum torque and power coefficients for the two stages rotor are 0.336 and 0.194, respectively. The power coefficient gain obtained by using the two stages Savonius rotor is 17.5 % compared to the conventional single stage which has a power coefficient of 0.165 at a wind velocity (V) of 6 m/s. Furthermore, using a multi-stage rotor significantly smooths the variations in the torque coefficient and produces positive static torque values at all rotational angles resulted in enhancing the self-starting capabilities of the Savonius rotor.

Aerodynamic and aeroacoustic performance investigations on modified H-rotor Darrieus wind turbine

2021 ◽  
pp. 0309524X2110039
Author(s):  
Amgad Dessoky ◽  
Thorsten Lutz ◽  
Ewald Krämer
Keyword(s):  
Wind Turbine ◽  
High Speed ◽  
Cfd Simulation ◽  
Vertical Axis ◽  
3D Models ◽  
Power Coefficient ◽  
Design Parameters ◽  
Second Phase ◽  
Vertical Axis Wind Turbine ◽  
Guide Vanes

The present paper investigates the aerodynamic and aeroacoustic characteristics of the H-rotor Darrieus vertical axis wind turbine (VAWT) combined with very promising energy conversion and steering technology; a fixed guide-vanes. The main scope of the current work is to enhance the aerodynamic performance and assess the noise production accomplished with such enhancement. The studies are carried out in two phases; the first phase is a parametric 2D CFD simulation employing the unsteady Reynolds-averaged Navier-Stokes (URANS) approach to optimize the design parameters of the guide-vanes. The second phase is a 3D CFD simulation of the full turbine using a higher-order numerical scheme and a hybrid RANS/LES (DDES) method. The guide-vanes show a superior power augmentation, about 42% increase in the power coefficient at λ = 2.75, with a slightly noisy operation and completely change the signal directivity. A remarkable difference in power coefficient is observed between 2D and 3D models at the high-speed ratios stems from the 3D effect. As a result, a 3D simulation of the capped Darrieus turbine is carried out, and then a noise assessment of such configuration is assessed. The results show a 20% increase in power coefficient by using the cap, without significant change in the noise signal.

Numerical Study of Pitch Angle on H-Type Vertical Axis Wind Turbine

2012 ◽  
Vol 499 ◽  
pp. 259-264
Author(s):  
Qi Yao ◽  
Ying Xue Yao ◽  
Liang Zhou ◽  
S.Y. Zheng
Keyword(s):  
Wind Turbine ◽  
Pitch Angle ◽  
Numerical Study ◽  
Vertical Axis ◽  
Azimuth Angle ◽  
Power Coefficient ◽  
Cfd Model ◽  
Vertical Axis Wind Turbine ◽  
Sliding Mesh ◽  
Mesh Technique

This paper presents a simulation study of an H-type vertical axis wind turbine. Two dimensional CFD model using sliding mesh technique was generated to help understand aerodynamics performance of this wind turbine. The effect of the pith angle on H-type vertical axis wind turbine was studied based on the computational model. As a result, this wind turbine could get the maximum power coefficient when pitch angle adjusted to a suited angle, furthermore, the effects of pitch angle and azimuth angle on single blade were investigated. The results will provide theoretical supports on study of variable pitch of wind turbine.

Numerical Research on the Characteristics of Lift-Drag Type Vertical Axis Wind Turbine

2012 ◽  
Vol 189 ◽  
pp. 448-452
Author(s):  
Yan Jun Chen ◽  
Guo Qing Wu ◽  
Yang Cao ◽  
Dian Gui Huang ◽  
Qin Wang ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Vertical Axis ◽  
Chord Length ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Tip Speed Ratio ◽  
Middle Range ◽  
Parabolic Form ◽  
Cfd Method

Numerical studies are conducted to research the performance of a kind of lift-drag type vertical axis wind turbine (VAWT) affected by solidity with the CFD method. Moving mesh technique is used to construct the model. The Spalart-Allmaras one equation turbulent model and the implicit coupled algorithm based on pressure are selected to solve the transient equations. In this research, how the tip speed ratio and the solidity of blade affect the power coefficient (Cp) of the small H-VAWT is analyzed. The results indicate that Cp curves exhibit approximate parabolic form with its maximum in the middle range of tip speed ratio. The two-blade wind turbine has the lowest Cp while the three-blade one is more powerful and the four-blade one brings the highest power. With the certain number of blades, there is a best chord length, and too long or too short chord length may reduce the Cp.

scholarly journals Double multiple stream tube theory coupled with dynamic stall and wake correction for aerodynamic investigation of vertical axis wind turbine

2020 ◽  
Vol 23 (4) ◽  
pp. 771-780
Author(s):  
Anh Ngoc VU ◽  
Ngoc Son Pham
Keyword(s):  
Wind Turbine ◽  
Shape Function ◽  
Vertical Axis ◽  
Transformation Method ◽  
Aerodynamic Performance ◽  
Dynamic Stall ◽  
Power Coefficient ◽  
Vertical Axis Wind Turbine ◽  
Stream Tube ◽  
Aerodynamic Investigation

This study describes an effectively analytic methodology to investigate the aerodynamic performance of H vertical axis wind turbine (H-VAWT). An in-house code based on double multiple stream tube theory (DMST) coupled with dynamic stall and wake correction is implemented to estimate the power coefficient. Design optimization of airfoil shape is conducted to study the influences of the dynamic stall and turbulent wakes. Airfoil shape is universally investigated by using the Class/Shape function transformation method. The airfoil study shows that the upper curve tends to be less convex than the lower curve in order to extract more energy of the wind upstream and generate less drag of the blade downstream. The optimal results show that the power coefficient increases by 6.5% with the new airfoil shape.

Computational fluid dynamic analysis of roof-mounted vertical-axis wind turbine with diffuser shroud, flange, and vanes

2018 ◽  
Vol 42 (4) ◽  
pp. 404-415
Author(s):  
H. Abu-Thuraia ◽  
C. Aygun ◽  
M. Paraschivoiu ◽  
M.A. Allard
Keyword(s):  
Wind Turbine ◽  
Urban Areas ◽  
Guide Vane ◽  
Fluid Dynamic ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Small Scale ◽  
Vertical Axis Wind Turbine ◽  
Guide Vanes ◽  
Turbine Design

Advances in wind power and tidal power have matured considerably to offer clean and sustainable energy alternatives. Nevertheless, distributed small-scale energy production from wind in urban areas has been disappointing because of very low efficiencies of the turbines. A novel wind turbine design — a seven-bladed Savonius vertical-axis wind turbine (VAWT) that is horizontally oriented inside a diffuser shroud and mounted on top of a building — has been shown to overcome the drawback of low efficiency. The objective this study was to analyze the performance of this novel wind turbine design for different wind directions and for different guide vanes placed at the entrance of the diffuser shroud. The flow field over the turbine and guide vanes was analyzed using computational fluid dynamics (CFD) on a 3D grid for multiple tip-speed ratios (TSRs). Four wind directions and three guide-vane angles were analyzed. The wind-direction analysis indicates that the power coefficient decreases to about half when the wind is oriented at 45° to the main axis of the turbine. The analysis of the guide vanes indicates a maximum power coefficient of 0.33 at a vane angle of 55°.

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