Experimental investigation on the effects of deflector angles on the power performance of a Savonius turbine for hydrokinetic applications in small rivers

A vertical-axis drag-driven Savonius turbine has various advantages and has demonstrated strong potential in hydrokinetic applications for sustainable rural electrification. However, its applicability is limited by the low coefficient of power inherent in the system. To solve this issue, the present study aims to evaluate the power performance improvement of a conventional Savonius turbine using two deflectors on the advancing and returning blades. Wind tunnel experiments conducted at Reynolds number, Re = 148,000 corresponding to 7.0 m/s (equivalent to 0.4 m/s water flow speed for hydrokinetic applications) revealed that, among the 30 deflector angle configurations tested, the advancing and returning blade deflectors were optimally configured at 30° and 90°, respectively. This combination of deflector angles resulted in the highest maximum coefficient of power at C_Pmax = 0.21, a 61.53% improvement relative to the case without the deflectors. This optimal configuration deflected the flow to the advancing blade while blocking the flow from impinging on the returning blade, effectively increasing the net positive torque and consequently the power performance. Moreover, it was found that variations in the returning blade deflector angle, δ_R had more significant effects on the turbine power than variations in the advancing blade deflector angle, δ_A. Conclusively, careful optimization of the deflector angle configurations was able to increase turbine power performance, suitable for practical implementation in small rivers with low flow rates for optimal power production.