MARKED CHANGE IN SUBCAVITATION CASCADE PERFORMANCE RESULTING FROM A VERY SLIGHT MODIFICATION IN LEADING EDGES

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