Abstract
Unsteady cavitating flows around two types of isolated two-dimensional hydrofoils, flat plate and Clark-Y 11.7％, are experimentally studied in order to understand the unsteady characteristics of cavitation instabilities. From visual observations using high-speed video cameras, the cavity length fluctuations with the cloud cavity formation from the trailing edge of attached cavity are investigated as well as cavity patterns such as patch, sheet（partial and super），shear, and so on. The pressure fluctuations near the leading and trailing edges of hydrofoil are measured simultaneously with high-speed camera recording, to relate the emitted pressure disturbances with sheet cavity fluctuations. It is found that, despite of large geometric
differences between hydrofoils, two types of cavitation instabilities, partial and transitional cavity oscillations, can occur
for both hydrofoils, provided the necessary flow conditions：the partial cavity oscillation occurs when the partial cavity
forms from near the leading edge of hydrofoil. The transitional cavity oscillation is unaffected by the location of the leading
edge of the cavity, and occurs when the trailing edge of the cavity becomes close to that of hydrofoil.
