Experimental investigation of a two-bladed double stage Savonius-akin hydrokinetic turbine at low flow velocity conditions

Abstract

Savonius-akin hydrokinetic turbine (SAHT) is a promising technology for generating hydropower from an ultra-low head condition with low flow velocity, wherein the kinetic energy of the free-stream flow is converted into mechanical power. The main drawback of SAHT is its lower efficiency. Therefore, the research works in this area is focussed towards improving the performance of such turbine by innovative design and development. The goal of the present work is to investigate the performance of a two-bladed two-stage vertical axis SAHT as a river-stream turbine by changing the gap/clearance between the stages. The stages are mounted on the shaft at 90° out of phase with each other. The gap between stages is varied from 0 to 20 mm in the increment of 5 mm. The experiments are performed under variable load conditions by considering different low flow velocities ranging from 0.4 to 0.6 m/s, commonly found in the perennial rivers. It is found that gap between the stage affects the performance of the SAHT. Based on the experimental results, the optimal loading condition as well as the optimal gap between the stages has been found out. Further, the maximum turbine power and the maximum coefficient of power (Cp) at corresponding TSR are also evaluated for the optimal conditions.