Design and performance investigation of a triple blade dual stage Savonius-alike hydrokinetic turbine from low flow stream reserves

Abstract

ABSTRACT A trending technology that is being employed to generate hydro energy from low-flow stream reserves is the Savonius-alike hydrokinetic turbine (SAHT). Clearance between the stages of a dual-stage two-bladed SAHT was found to improve its performance at low flow speeds; however, the impact of clearance on the triple-bladed configuration of SAHT was not studied earlier. In this paper, a triple blade dual stage configuration of SAHT is designed, and its performance is investigated in a water flume under various stage clearances (0,5,10,15 and 20 mm), low flow speeds (0.45,0.55 and 0.65 m/s) and different brake loads. Detailed turbine performance under different design and off-design conditions are investigated to obtain meaningful performance insights. The findings show that torque production by the turbine increases with the increase of brake load, with maximum hydrodynamic torque generated at the highest brake load. The highest coefficient of performance and torque of 0.071 and 0.261 are obtained at a stage clearance of 5 mm, tip speed ratio of 0.273, and free-stream flow speed of 0.55 m/s. The present SAHT under design condition has improved performance compared to a dual blade dual stage SAHT exhibiting a wider tip speed ratio range for its application in low flow stream reserves. Further, this turbine may also be recommended for torque generation to work as a motor in a flow speed condition less than 0.5 m/s. The novelty of this work is the application of an additional flow control measure in the form of flow-through clearance to negotiate vertical water thrust through the clearance and exert additional pressure on the advancing blades of the SAHT in the upper stage.