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 o f the roll-up vortex on the suction side of a Kaplan-type turbine blade wit h various endings is investigated. Measurements are made on different model s with simplified two-dimensional geometries using mainly particle image ve locimetry. It is found that the greatest danger of cavitation erosion exist s when the casing of the turbine is of the "semi-spherical" type, so that t here 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 ine ffective at increasing the distance of the vortex from the blade, although it does reduce the circulation of the vortex and presumably the danger of c avitation. Our measurements are found to be in good agreement with existing models for the position of the vortex when appropriately interpreted.