Marked Change in Subcavitation-Cascade Performance Resulting from a Very Slight Modification in Leading Edges

Abstract

As a first step to finding thin, low-drag foils in cascades applicable to Kaplan turbines of high specific speed, we systematically investigate the subcavitation performance and the cavitation aspects, especially those of the leading-edge separation bubble related to the drag, for two foils whose shapes are very similar, except for two percent of the total area near the leading edge contained by a chord, with somewhat modified edges, for various cavitation numbers and incidences. A marked change in drag results from a very small modification in the edge, and it is closely related to the stochastical appearance of the leading-edge separation bubble visualized through the attached cavitation.