A ducted Darrieus-type turbine has been proposed for extra-low head hydropower utilization of total head less than 2m. In the case of installing the runner in the duct, a narrow intake type brings about higher efficiency than that of the parallel intake with the same width of runner shaft section. In the latter application, the clearance between the casing wall and the runner pitch circle roles an important factor for turbine performance as flow distortion occurs toward the side wall and the main flow is decreased through the center passage of duct. Then, turbine performance is severely deteriorated. On the other hand in the former application, effects of the clearance on turbine performance are not clarified yet, though the flow distortion is supposed to become weakened because of the narrow intake before the runner. In the present paper, the effects on turbine performance are experimentally examined with help of flow measurement and the results are compared with the results of parallel walls. Then, it is shown that there is little influence of the casing clearance on the efficiency and without deteriorating turbine efficiency the structure of turbine enables to become simplified by removing the side-wall at the runner section and the draft tube downstream of runner.

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Development of high specific speed turbine is one of the countermeasure to environment issue. However, the higher specific speed of multi-jet Pelton turbine can leads to the jet interference in the low head, high discharge operation conditions and it causes extraordinary efficiency drop. Authors measured the performance around the jet interference occurring region in prototype and recognized the jet interference starting line is different between model and proto type. On the other hand, FAM, which is the prediction method of the jet interference starting line studied by authors showed a good agreement with the proto type test result. In this study, model test results in which the test head is changed are compared with the FAM results. As the result, a good agreement between analysis results and model test results is obtained.

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The effects of the return vane profile on the multistage turbopump efficiency were investigated experimentally, taking account of the inlet flow condition for the next stage impeller. It is desirable to set the trailing edge of the return vane on the outer diameter position of next stage suction cover. Then, the swirl stop ranging the trailing edge and the main shaft contributes fruitfully to suppress the unstable performance at the low discharge.

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In the low specific speed range, performance improvement of centrifugal pump is one of the important issues. The present study is focused on performance improvement in the range of low specific speed, and a new type centrifugal impeller with J-Groove mounted at the back of both front and rear shroud is proposed and tested. The results show that the proposed device is effective in the range of n_s<150(m, m³ / min, min^-1). J-Groove raises up pumping head by 25%, which is caused by rapid increase of fluid velocity in a volute. In addition, the unstable head-capacity curve becomes stable. It is also clarified that the reduction of impeller diameter is possible without changing the pump overall performances.

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In a high specific speed pump, such as a mixed flow or an axial flow pump, the head-capacity curve tends to have a rising characteristic, which is called "performance curve instability". To improve this unstable performance, an innovative technique using shallow grooves mounted on an inner casing wall (called J-Grooves) had been developed. By J-Groove, a performance curve instability of a mixed-flow pump was completely suppressed without dropping the maximum efficiency, but it is still difficult to suppress the instability in an axial flow pump without dropping the maximum efficiency.
The present study is aimed to attain complete suppression of the performance curve instability with keeping the maximum efficiency in an axial flow pump, and a new type J-Groove technique was developed using the axial flow pump of specific speed n_s=2000(min^-1, m³/min, m).

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The resonant condition by the interaction between the impellers and the stationary parts of the centrifugal compressor has been experimentally investigated. The two types of the diffuser were examined, which is vaneless and vaned diffuser. The 5^th nodal diameter mode of the natural frequency was highly excited by the vaned diffuser, which is installed just downstream of the impeller. This resonance can be verified by the interaction theory between the pressure distribution around the impeller and nodal diameter mode of the impeller natural frequency.
The distance between the impeller outlet and leading edge of the diffuser vane is proved to be the critical parameter of the magnitude of the resonance.

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In this paper, vibration phenomena of a curved pipe with a guide vane were considered. In order to decide analysis conditions of Computational Fluid Dynamics (CFD) based on Large Eddy Simulation (LES), CFD results were compared to Particle Image Velocimetry (PIV) results for a downscale model. Moreover, Fluid-Structure Interaction Analysis was conducted for the elbow pipe fitting having actual size. As a result of this analysis, stress fluctuation on the trailing edge of the guide vane was largest. This result indicates that vibration phenomena are possible to occur on the trailing edge of the guide vane.

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