Impact of inner blades on power and torque of Savonius rotor through wind tunnel experiments

Energy crisis due to fast globalization and the negative effects of global warming compels a greater need for nonconventional energy sources. Solar and wind power are the primary sources of renewable energy used to meet the power demand. Savonius rotor, a kind of vertical-axis wind turbine, whose operation is dependent upon drag force, has many benefits, including low operating speeds, good self-starting ability, ease of installation, design simplicity, and wind direction independence. However, the low efficiency of the turbine caused by the negative torque it produces on the returning blade limits the applicability of the turbine. The present work experimentally investigated the possibility of performance improvement of the turbine by incorporating inner blades. A 3-bladed configuration of the turbine containing 2 inner blades and an outer semi-circular blade was designed and constructed for performance assessment using an open circuit wind tunnel. Three turbine configurations with 160º inner blade angle and 2 cm spacing between the blades were tested for optimal performance. The performance was evaluated for different wind velocities by fixing the test setup at the wind tunnel outlet. The rotational speed and torque were measured using a rope break dynamometer and tachometer, respectively. The result indicated that using 1 inner arc blade improved the maximum power coefficient and torque coefficient of the rotor by 33.17% and 8.89%, respectively, compared to the conventional configuration. However, using 2 inner blades reduced the maximum power coefficient and torque coefficient by 37.43% and 46.67%, respectively. The maximum value of the power coefficient was found at tip speed ratios (TSRs) between 0.25 and 0.45, whereas the torque coefficient declined with the increase of TSR for all 3 configurations. Moreover, the maximum power coefficient and torque were observed at lower wind speeds.