No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Abstract
A new vertical-axis spiral wind blade was proposed. The relation between flow characteristics around the blade and torque property of the blade was studied. With computational fluid dynamics (CFD) technology and Spalart-Allmaras turbulence model, three-dimensional flows inside and outside the two-blade rotor were numerically simulated. The torque coefficient under rated wind speed was analyzed. At upper stream velocity of 4m/s, flow parameter distributions under maximum and minimum torque coefficient conditions were compared. The results indicate that torque property of the presented rotor is satisfying. Pressure difference between pressure and suction surfaces of the blade, position of large-scale low-pressure zone are two critical factors affecting torque production. Flows around the blade are evident three-dimensional spatial flow patterns. The study provides helpful references for further improvement and aerodynamics analysis of Savonius rotor.
... The benefits of replacing straight blades with curved blades have been demonstrated by improved flow patterns and decreased aerodynamic force variability [85][86][87][88]. Because of their low cut-in wind speeds and ability to selfstart, these turbine rotors have gained some acceptance. ...
The vertical-axis Savonius wind rotor is known for its design simplicity, better starting qualities, and direction independency despite its inferior efficiency when measured against certain other types of vertical-axis wind rotors. Despite a plethora of research work on Savonius rotors, an in-depth analysis of Reynolds number (Re) on aerodynamic and power coefficients of the Savonius rotors is scarce. This paper aims at understanding the influence of Re on the performance of a novel parabolic blade profile through unsteady two-dimensional (2D) computation. The Reynolds-averaged Navier Stokes (RANS) equations are modelled using the ANSYS-Fluent by adopting shear stress transport (SST) k-ω turbulence model. The computational results of the novel blade profile are then compared and analysed with an established semicircular blade profile to draw some meaningful insights into the aerodynamic performance. In the tested range of Re = 5.3 × 104 − 10.6 × 104, the novel parabolic blade profile outperformed the semicircular blade profile in terms of aerodynamic and performance coefficients.
The eminent energy crisis and high emission of fossil fuels provide thrust for developing renewable energy-based technologies. Wind and hydrokinetic energies are the most promising renewable energy resources for electric power generation to meet the growing energy demand. The vertical-axis hybrid turbine, which combines the features of good starting characteristics of the Savonius turbine and the operational efficiency of the Darrieus turbine, can serve as a viable option for power generation. A variety of configurations of the hybrid turbine are possible based on several design parameters such as the relative position of the Darrieus and Savonius rotors, overlap ratio, solidity ratio, blade or buckets shape and radius ratio, attachment angle and others. To some extent, the influence of these parameters on the hybrid turbine performance has been investigated through experimental and numerical studies by considering a number of physical and computational models. In most of the findings, the range of maximum power coefficient values is recorded between 0.08 and 0.51. Though individual vertical axis turbines have been widely studied and reviewed, similar review papers on hybrid turbines are scarce. This paper brings out significant developments that have taken place in the area of hybrid turbines, identifies the operating parameters, highlights the challenges related to rotor/turbine aerodynamics, modelling, simulation, testing methodologies. Based on these discussions, the strategies for future hybrid turbine designs are presented.
The Savonius wind turbine bears unique features in both aspects of rotor structure and torque production. Continual improvement of the Savonius wind turbine motivates the authors of this review to gather, classify and discuss the quintessential parts of the relevant studies. Unambiguous priority is granted to the turbulent flow surrounding the Savonius wind rotor. Flow patterns near the Savonius wind rotor are represented with distributions of static pressure near conventional and spiral Savonius wind rotors. Assorted geometric shapes of Savonius wind rotors are demonstrated to illuminate a panorama of the development of the Savonius wind rotor, as well as to highlight the connection between rotor-based solid boundary and flow structures near Savonius wind rotor blades. Limitations of existing analytical methods used to predict the performance of the Savonius wind rotor are interpreted. Advantages of both numerical and experimental techniques in acquiring aerodynamics forces, shaft torque and internal stress distribution for the Savonius wind rotor blade are enumerated, and the difficulties incurred by curved blades and the rotation of the rotor are analyzed as well. Optimal values of tip-speed ratio corresponding to maximum power coefficient or maximum torque coefficient are different for various geometric shapes of Savonius wind rotors, which sheds new light upon the relationship between flow characteristics and performance parameters associated with the Savonius wind rotor.
Flow in and around a Savonius rotor has been studied by flow visualization experiments, and the rotation effect is discussed in comparison with the measured pressure distributions on the blade surfaces. It is observed that the flow separating regions on the blade surfaces are fairly reduced by the rotation effect and the flow through the overlap is weakened by the appearance of resisting flow. The former contributes to the torque production of the rotating rotor while the latter acts as a resistance. These phenomena together with the stagnation effect on the front side of the rotor contribute to the power producing mechanism of the Savonius rotor.