A Marked Change in Subcavitating-Cascade-Performance Resulted from a Very Small Modification in Leading Edges.

For the first step to find low-drag thin hydrofoils in cascade applicable to Kaplan-turbines, the subcavitating performance and the corresponding cavitation aspects for two different hydrofoils whose shapes are quite the same except the neighborhood of the leading edge within one percent chord. The leading edges are somewhat modified, for two cascade arrangements of a pitch-chordratio t/l=1.14 and of two cascade angles θ1=23°and 35°, for various cavitation numbers and various incidences. Clearly, a marked change in drag is resulted from such a very small modification around the edge, which is closely related to the boundary layer separation around the leading edge. It is also suggested to the suitable modifications without separation bubble.