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The Savonius rotor is a drag-based vertical axis wind turbine and is used as an alternative source in small-scale energy generation. Design simplicity, low-cost, easy installation, good starting ability, relatively low operating speed and independent to wind directions are the main advantages of this rotor. However, because of its low efficiency and high negative torque produced by the returning blade, this rotor concept rarely gained popularity. Over the last few decades, although a number of investigations around the world have reported performance gains of the Savonius rotor, the available technical design is still not able to fulfill the demand of efficient small-scale wind energy converter at low wind speeds. Until now, various design changes have been proposed to meet a growth in power output through optimization of influencing variables like aspect ratio, overlap ratio, blade material, and so forth. Investigations have also been carried out by installing additional devices like curtain design, deflector plate, nozzle and ducts, multi-staging, guide-box tunnel and windshields. Installation of these devices considerably reduced the negative torque as well as improved the starting performance of the rotor. As a result, the power output of the rotor is also improved. Several researchers have reported increased power coefficients for various rotor designs based on their different testing parameters. Power coefficients for the conventional Savonius rotors have been mostly reported in the range of 0.12-0.18 and by optimizing its design, it can reach as high as 0.38. This article attempts to discuss the various influencing parameters as well as the augmentation techniques. This would offer an overall idea on the progress that has taken place to improve the design and performance of the Savonius rotor.

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WOS:000393726200034International audienceIn this paper, Direct Numerical Simulations (DNS) are carried out in order to capture the flow instabilities and transition to turbulence occurring on a Savonius style wind turbine (SSWT) blade. Simulations are conducted with the open source code NEK5000, solving the incompressible Navier-Stokes equations with a high order, spectral element method. Because of the relatively high Reynolds number considered (Re xi = 9 x 10(4)), the computational domain of the Savonius blade is reduced to the pressure side, and the blade is studied in static condition, which avoids the large scale vortex shedding that occurs on its suction side, particularly allows to investigate the static performance of the wind turbine. The results suggest that Gortler vortices can occur and cause the flow to transit to turbulence, which modify the pressure and wall friction distributions, and consequently alter the drag and lift forces. (C) 2016 Elsevier Ltd. All rights reserved

Rapid depletion rate of fossil fuels with an increasing energy demand and their high emission are imposing the evolution activities in the arena of renewable energy. To meet the future demands of renewable energy sources, wind energy is a very promising concept. In this feature, the drag based vertical axis wind turbines (VAWTs) are suitable for small scale wind energy generation for decentralized locations. However, these turbines have low power and torque coefficients as compared to other wind turbines. Numerous blade shapes have been proposed till now to improve the performance of these turbines. In the present paper, a computational study has been performed to simulate the air-flow over different blade profiles using shear stress transport (SST) k–ω turbulence model. The results obtained are validated with the available experimental data. In the dynamic simulations, the power and torque coefficients are calculated considering the blade arc angle as the variable shape parameter. The effects of drag and lift forces on the variable blade shapes are also studied in static simulations at various angular positions. The present paper tries to demonstrate an effective computational methodology to predict the flow behavior around a drag based VAWT. Through this study, it has been found possible to select an optimal blade shape from the point of its aerodynamic performance.