Application of Counter Rotating Rotors for Improving Performance of Savonius Turbines
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RESEARCH PAPER
Application of Counter Rotating Rotors for Improving Performance of Savonius Turbines Vahid Etemadeasl1 · Rasool Esmaelnajad2 · Babak Farzaneh1 · Moharram Jafari2 Received: 21 January 2019 / Accepted: 1 November 2020 © Shiraz University 2020
Abstract In this paper, a new configuration is proposed for using Savonius rotors by installing two Counter-Rotating Savonius Rotors (CRSR) together. In order to study the aerodynamic performance of the CRSR turbine, 2D unsteady turbulent flow around the CRSR turbine is simulated using commercial CFD software ANSYS-Fluent16.0. Turbulence modeling is done using k − 𝜔 SST model. Numerical results demonstrate a considerable improvement in aerodynamic performance of the CRSR turbine in comparison to a single conventional rotor. Effect of the distance between two rotors and different angular positions of two rotors on the CRSR turbine performance is studied. It is shown that the most effective parameter influencing the performance of the CRSR turbine is the distance between the rotors. Numerical results reveal that, locating two rotors in an optimal phase angle (θ = 90) and distance(S = 1.0D0), average power coefficient of the CRSR turbine can be increased to 21%, which indicates a rise of 38% compared to conventional Savonius rotors. Keywords Savonius rotor · Counter-rotating rotors · Aerodynamic performance · Vertical axis wind turbine (VAWT) Nomenclature AS Turbine swept area CP Power coefficient CPave Average power coefficient CT Torque coefficient d Bucket diameter D Rotor diameter D0 Rotation zone diameter D Rotor diameter a/D Blades Overlap ratio H Rotor height R Blade radius S Gap distance between adjacent turbines blade tips t Blade thickness T Torque U Wind velocity λ Tip speed ratio θ Relative phase angle between rotors ω Angular velocity (rad/s) * Rasool Esmaelnajad [email protected] 1
Young Researchers and Elite Club, Ardabil Branch, Islamic Azad University, Ardabil, Iran
Department of Mechanical Engineering, University of Tabriz, Tabriz, Iran
2
ρ Density α Angular position of a rotor
1 Introduction In recent decades, increasing energy demand and climate change caused by fossil fuels have enhanced the interest in renewable energy resources. Lower costs of maintenance and operation, as well as the absence of fuel consumption, are among the most important advantages of the wind energy in comparison to other sources of renewable energy. Lower production cost and less starting wind speed in comparison to Horizontal Axis Wind Turbines (HAWT) are the most important advantages of Vertical Axis Wind Turbines (VAWT) (Paraschivoiu 2002; Muscolo and Molfino 2014). Savonius rotor is one of the simplest types of VAWT in terms of design and manufacturability (Schubel and Crossley 2012). This rotor has two convex and concave surfaces that are located in the wind direction. It is rotated by an imbalanced drag force exerted on these surfaces. The blade with concave side against the flow producing negative torque is called returning
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