Influence of a deflector on a self-starting speed and power performance of a two-bladed Savonius hydrokinetic turbine

The aim of this study is to investigate the self-starting speed and power performance of a 2-bladed Savonius rotor turbine for hydrokinetic application with the presence of a deflector. Experiments were performed in a closed-circuit wind tunnel under two cases: with and without a deflector. First, the self-starting speed of the turbine was characterised at different rotor angles for various deflector angles ranging from 30° to 120° where the coefficient of the static torque was also acquired. Based on the self-starting speed of the turbine, the power performance, in terms of coefficients of power and torque, were acquired and compared. The study found that the deflector reduced the self-starting speed of the turbine with the highest reduction, which occurred when the deflector was configured at 90°. At this optimal deflector angle, the lowest self-starting speed of the turbine was found to be 5.1 m/s air flow speed (equivalent to 0.29 m/s water flow speed) where it had reduced by 38.55%, relative to the baseline case. Moreover, the turbine exhibited the highest coefficients of static torque for all the deflector angles considered in this study. Besides, the coefficient of power had significantly improved by 84.62%, and the range of tip speed ratio also increased which indicated the capability of the turbine to generate more power. With the presence of a deflector, the returning blade was blocked from the incoming flow, thus reducing the negative torque on the blade that opposed the turbine’s rotational motion. The comparisons of the turbines’ performance indicated that the turbine with a deflector operating under low flow rate condition was capable of generating a marginally more substantial amount of power compared to the turbine with no deflector, which operated under a high flow rate. This study demonstrated the effectiveness of the deflector to improve the operating range and performance of the Savonius turbine under low water flow speed condition for hydrokinetic application without deteriorating the turbine performance. Therefore, it can be suitably adopted for low load applications to provide sustainable electrical power, especially in remote areas with extensive river networks such as those found in Malaysia.