The Archimedes screw turbine differs considerably from other water turbines in terms of its structure. In this report, its unique losses are defined, and a calculation method for each loss is proposed. The larger the number of blades, the smaller is the water level difference between the upstream and the downstream sides of the blade. Therefore, if the blade tip clearance is constant, there is a reduction in leakage because of the decreasing pressure difference, and the discharge efficiency is increased. In addition, the boundary layers on the casing wall surface are scraped away by the blades. This causes loss, and a prediction method for shaft power is proposed, considering this loss. It was confirmed that the shaft power predicted using this method and the shaft power obtained experimentally are in good agreement over a wide range of rotational speeds, except for the low speed range.

This paper investigates the influence of pressure-side separation on the aerodynamic performance of high-lift LP turbine cascades by varying the thickness of airfoils. A linear cascade test facility is employed and a miniature pitot tube and hot-wire probe measurements are performed along with LES simulation. In the experiment, as the airfoil thickness is increased with the suction surface shape unchanged, total pressure loss on the pressure-side decreases probably because of the suppression of pressure-side separation, leading to reduction of cascade loss. However, an excessive increase of the airfoil thickness causes a higher peak in the airfoil loading distribution, resulting in early boundary layer separation on the suction-side. As a result, the thickest airfoil yields an increase in cascade loss. In the LES analysis, it is found that the vortex released from the pressure-side separation bubble generates a total pressure loss in the pressure-side region in baseline airfoils.