24. Performance Improvement of Contra-Rotating Small Hydroturbine

Pico hydropower, which generates about 100 W–1 kW, is called new energy in Japan, and there are a lot of places suitable for the pico-hydropower in agricultural water and a small stream. Efficiency of the pico-hydroturbines is lower than that of large one and it can be used in wide flow rates range. There are inline agricultural water and small water-supply system for mountainous village, which use the high elevation over 30 m from the dam, in Tokushima Prefecture of Japan. In this research, we designed the inline small hydroturbine using the contra-rotating rotor, which can be applied for the above facility with 2 inches’ pipe. The maximum static pressure efficiency over 64% was obtained by the experiment in the previous research. In order to improve the performance of small hydroturbine, the tip clearance and solidity are varied from the base model using the numerical analysis model, and the numerical analysis is conducted with steady condition to reduce the computational cost. It is found that the efficiency increases about 10% with the decrease of the tip clearance from 1.0 mm to 0.5 mm at the design flow rate 1.0 Qd. The solidity of each front and rear rotor is optimized and the numerical analysis is conducted with the unsteady condition for the best solidity combination model. The maximum total pressure efficiency over 68% is obtained for the best solidity model at the 1.25 Qd. The pressure distribution in axial direction of each type of the model is investigated by the numerical analysis results.