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Cavitation of a hydrofoil is observed in detail by using a high speed video camera. Paint removal test is also carried out in order to evaluate cavitation aggressiveness for erosion. 2D hydrofoil profile is Clark Y 11.7% and its angle of attack is seven degrees. Cavitation number is σ=1.08. Experimental results are compared with cavitation CFD. Numerous features of unsteady cavitation are observed such as cyclic fluctuation of sheet cavity, existence of glassy cones on a sheet cavity, generation of cloud cavitation from sheet cavity and isolated bubbles traveling over suction surface of the blade. Isolated traveling bubbles and their collapses are thought to be one of the main causes of severe paint removals. Isolated traveling bubbles are derived from flowing cavitation nucleus or from abrupt generation at the leading edge of the blade. Some important factors of computation are clarified for the modification of cavitation CFD.

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A ducted Darrieus-type turbine has been proposed for extra-low head hydropower utilization of total head less than 2m. Though the hydro turbine system, in general, might consist of an intake, runner section and the draft tube for higher efficiency operation, in the case of duct with an inlet nozzle, it was clarified in previous experiment that there was no need of the side-walls of runner section and a draft-tube for keeping high performance, which yields a simplification of the structure of the turbine system. In order to reconfirm this result for large-sized turbine with 400×500 mm duct, instead of small-sized one with 400×200 mm, the side-wall effect on turbine performance was experimentally investigated for three- or four-bladed runner. In the present paper, the experimental results are shown with considering flow behaviors in the runner section.

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