Experimental investigation into the effects of endplate designs for a Savonius turbine

Abstract

Wind energy is experiencing a trend of exponential growth in both literature and industrial employment, emphasizing its current pivotal role in achieving carbon neutrality by replacing fossil fuels. Vertical axis wind turbines (VAWTs) particularly Savonius rotors operate at a lower tip-speed-ratio (TSR) range compared to horizontal axis wind turbines (HAWTs). The Savonius rotor has good starting characteristics, making it suitable to be placed in urban areas with lower wind speeds. Due to its low efficiency, studies on augmentation and optimization have been conducted to improve its blade and deflector designs. Extensive research has established a common consensus that the use of endplates significantly improves the aerodynamic performance of the Savonius rotor. However, limited research has been undertaken to explore the endplate design further. In this study, wind tunnel tests were conducted on different endplate ratios, to investigate the effects of endplate design on the aerodynamic performance of a conventional Savonius turbine. Three different Savonius rotor with no endplate, semi-circular endplate and circular endplate were designed and manufactured. Experiments were conducted in an open-type suction wind tunnel at a constant measured wind velocity of 5.89 m/s. The turbine’s performance for different endplate ratios was evaluated across a TSR range of 0.2 to 1.0. The performance was assessed based on the maximum power generated and its self-starting ability. From the experimental results, the circular endplate ratio of 1.1 shows a significantly high coefficient of power compared to both semi-circular and without endplates. This is due to reduced spanwise spillage and enhanced airflow capture by the rotor. The endplates direct incoming air to the advancing blade and overlap region, resulting in the increased pressure difference between the concave and convex sides of both the advancing and returning blade, thereby improving the power efficiency of the turbine with 1.1D diameter endplate and semi-circular endplate by 296.6% and 6.9% compared to no endplates case.