The role of wake splitter deflector on performance enhancement of Savonius wind turbine

Abstract

The Savonius drag-type wind turbine suffers from poor efficiency due to the adverse negative torques on the returning blades when they rotate against incoming flows. It was proven that using a suitable deflector system has the potential to improve wind turbine efficiency. However, as previously identified in studies, the common drawback of using a flat deflector is the strong wake zone behind it. The present study aims to improve the overall performance of a drag-type wind turbine by using a cylinder deflector with a wake splitter plate to manage and mitigate the detrimental effect of the wake zone behind the deflector. The wake control and suppressing vortex shedding downstream of a circular cylinder have been divided into active and passive flow control techniques. Amid the latter control methods, the adoption of splitter plates has proven to be highly effective for wake control and suppressing vortex shedding behind the cylinder. Unlike previous studies, a cylinder deflector with the wake splitter plate will be utilized instead of the conventional deflectors to improve the efficiency of the wind turbine by disturbing the wake zone downstream of the deflector. To obtain a more efficient configuration, the effect of the variations of the wake splitter length (Ls/D), attachment angle (θwsp), and the count of wake splitters on the outputs such as generated torque coefficient (Cm), power coefficient (CP), and wake zone on the performance of the Savonius rotor were investigated via Computational Fluid Dynamics simulation. The results revealed that cylinder deflectors with the wake splitter increased the Savonius rotor's performance the most for almost all Tip Speed Ratios (TSRs). The average Cm and CP raised considerably up to 15% using a deflector with two wake splitters at TSR = 0.6 compared to the case without deflectors.