Small hydropower generation is one of important alternative energy, and potential of small hydropower is great. Efficiency of small hydroturbines is lower than that of large one, and these small hydroturbine’s common problems are out of operation by foreign materials. Then, there are demands for small hydroturbines to keep high performance and wide flow passage. Therefore, we adopted contra-rotating rotors, which can be expected to achieve high performance and enable to use low-solidity rotors with wide flow passage, in order to accomplish high performance and stable operation. Final goal of this study is development of a small hydroturbine like electrical goods, which has high portability and makes an effective use of unused small hydro power energy source. Efficiency of the contra-rotating small hydroturbine was high in pico-hydroturbine and high efficiency could be kept in wide flow rate range. On the other hand, the relatively large loss occurred at the spokes which should be installed for this small hydroturbine to support the rotors. Then, the new spoke to increase its performance is proposed in this research. Internal flow condition, which was difficult to measure experimentally, was shown by the numerical flow analysis. Further, the influence of spoke geometry was clarified. Then, a relation between the performance and internal flow condition was considered by the numerical analysis results.
In the present paper, the performance of the contra-rotating small hydroturbine using different spoke geometry is shown by the numerical results. Further, internal flow condition between the front and rear rotors are investigated.