A ducted Darrieus-type hydro turbine has been proposed for utilization of extra-low head hydropower less than 2 m. In general, the low head hydro turbine system demands the simple structure to reduce the cost of power generation. The Darrieus-type hydro turbine is cross flow type and takes larger values of generated torque with higher efficiency on the upstream path of the Darrieus blades passing in one revolution. Based on this reason, when a narrow intake at the upstream of the runner, called as "inlet nozzle", is installed, the performance of Darrieus-type hydro turbine becomes higher than that without one. In addition, it is possible to remove the draft tube and side-walls of the runner casing keeping the turbine efficiency high. In the present paper, more simplified runner casing, composed of only the inlet nozzle and the small upper-casing, is proposed and the experimental results are shown.
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