Performance evaluation of a pilot-scale two-stage Savonius turbine for low-speed flow

The Savonius hydrokinetic turbine offers a promising method for harnessing low-speed oceanic flow energy due to its self-starting capability. In this study, a pilot-scale, two-stage Savonius turbine with two semi-circular blades per stage, offset by 90° was designed. The turbine's hydrokinetic performance was first evaluated in a flume. A complete turbine system was assembled by integrating a customized generator, then tested in the flume to measure start-up velocity and power output. Based on the flume test results, the generator was optimized for higher efficiency before real-seal deployment and evaluation. The results demonstrated the system achieved successful start-up at minimum flow velocities of 0.3 m/s (flume) and 0.26 m/s (sea). Both torque and power output increased with higher flow velocities, and the maximum power coefficient at each flow velocity was achieved at a specific Tip Speed Ratio (TSR) between 0.7 and 0.8. The upgraded generator significantly improved the system's electrical power output efficiency, from 15 % at 0.3 m/s in the flume to 43 % at 0.26 m/s in the sea. Design challenges identified during testing were discussed for further optimization. These findings underscore the potential of the Savonius turbine system as a viable option for capturing low-speed flow energy in marine environments.