In this study, a comparison of two different Kaplan turbine runners with differently shaped turbine blades was performed. The two turbines differed in the selection of the hydrofoil, the main hydrofoil parameters of which had been modified including, the position of maximum thickness and curvature and the inlet edge radius. Both turbines (unmodified and modified hydrofoils) were tested on a rig designed for low pressure model turbine acceptance tests. The effect of blade shape on cavitation inception, development, and intensity was demonstrated using computer aided visualization. Visualization was performed on the suction side of Kaplan runner blade where the shape of the blade determines cavitation inception and development. The modified Kaplan turbine reduced the cavitation phenomena, and as a result, both turbine performance and output increased for the selected operating points. This demonstrates that choosing the right turbine blade shape is key for optimal turbine performance.
The influence of a bulb runner blade hydrofoil shape on flow characteristics around the blade was studied. Experimental work was performed on a bulb turbine measuring station and a single hydrofoil in a cavitating tunnel. In the cavitation tunnel, flow visualization was performed on the hydrofoil’s suction side. Cavitation structures were observed for several cavitation numbers. Cavitation was less intense on the modified hydrofoil than on the original hydrofoil, delaying the cavitation onset by several tenths in cavitation number. The results of the visualization in the cavitation tunnel show that modifying the existing hydrofoil design parameters played a key role in reducing the cavitation inception and development, as well as the size of the cavitation structures. A regression model was produced for cavitation cloud length. The results of the regression model show that cavitation length is dependent on Reynolds’s number and the cavitation number. The coefficients of determination for both the existing and modified hydrofoils were reasonably high, with R2 values above 0.95. The results of the cavitation length regression model also confirm that the modified hydrofoil exhibits improved the cavitation properties.
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