High Specific-Speed Kaplan Turbine-Cascade Whose Perfomance Scarcely Changes with Cavitation Number

In order to find low-drag thin hydorfoils in cascades applicable to Kaplan turbines, we systematically investigate the subcavitating perfomance and the cavitation aspects around circular-shape hydrofoils for two cascade arrangements of various cavitation numbers and incidences. Our previous paper showed that the separation bubble near the leading edge, especially a long bubble, markedly increases the drag for thin hydrofoils in the cascade of present interest. Hence we investigate the behavior of the long bubble here. We try to suppress the long bubble, so that there is a marked increase in drag, by applying accelerating cascade effects of high-cambered hydrofoils effectively. We find a superior cascade hydorfoil, whose perfomance scarcely changes with cavitation number.