Measurements of tip vortex characteristics and the effect of an anti-cavitation lip on a model Kaplan turbine blade

Motivated by the problem of cavitation erosion, the position and strength of the roll-up vortex on the suction side of a Kaplan-type turbine blade with various endings is investigated. Measurements are made on different models with simplified two-dimensional geometries using mainly particle image velocimetry. It is found that the greatest danger of cavitation erosion exists when the casing of the turbine is of the "semi-spherical" type, so that there is a large and closing clearance gap at the leading edge of the blade. Furthermore, the anti-cavitation lip used in this study is shown to be ineffective at increasing the distance of the vortex from the blade, although it does reduce the circulation of the vortex and presumably the danger of cavitation. Our measurements are found to be in good agreement with existing models for the position of the vortex when appropriately interpreted.