Effect of Semi-elliptical Outer Blade-surface on the Savonius Hydrokinetic Turbine Performance: A Numerical Investigation

The Savonius hydrokinetic turbine (SHT) is widely used for generating electricity from running water. However, most optimization work has been carried out on conventional blades with similar concave and convex profiles. This study aims to enhance SHT performance by modifying the rotor blades' outer surface radius (۰.۰۷۹, ۰.۰۸۷ and ۰.۰۹۵ m) to create a semi-elliptical shape, thus reducing opposing forces. The tip speed ratio (TSR) varies from ۰.۵ to ۱.۳ with an interval of ۰.۱. A constant channel velocity of ۰.۸ m/s at Re = ۲.۲۵ × ۱۰۵ is considered for the analysis. The flow field has been numerically investigated using the SST k - ω model. This study comprises the angular variation in the coefficients of power (Cp) and torque (Cm), performance curves of the rotor, and pressure distribution on the blade surface at different angular positions. It is observed that the rotor with a radius of ۰.۰۹۵ m has a maximum Cp value of ۰.۱۴۲, which is ۷.۵۷% and ۱۸.۳۳% higher than the Cp values of rotors with radii of ۰.۰۷۹ m and ۰.۰۸۷ m, respectively. The maximum power output of the rotor with a radius of ۰.۰۹۵ m is ۲.۳۲ W, whereas the power outputs of the rotors with radii of ۰.۰۸۷ m and ۰.۰۷۹ m are ۲.۱۶ W and ۱.۹۶ W, respectively. An increase in the instantaneous values of Cm between rotation angles ۰◦ to ۱۱۵◦ is observed, during which the returning blades mainly interact with the incoming stream. The pressure decreases as the radius of the semi-elliptical outer surface increases at rotor positions ranging from ۰◦ to ۲۲۵◦, but it increases at rotor positions ranging from ۲۷۰◦ to ۳۱۵◦.

کلیدواژه ها:

SHT ، Power and torque coefficients ، SST k - ω model ، Flow characteristics ، Computational fluid dynamics ، OpenFOAM