Experimental investagations on the dynamic of cavitating flow around a cascade of hydrofoil

The flow structure and the dynamics of cavitating flow in a cascade of hydrofoil are investigated experimentally. Experiments are conducted in a cavitation tunnel and situations ranging from non cavitation to unsteady cloud cavitation are obtained by varying the Reynolds number and the cavitation numbers. The instantaneous shapes of the cavity are observed by high-speed video and high-speed photo. The frequency of cavitating oscillation is obtained by the lift/drag measurements. From the results of experiments, the lift/drag of the hydrofoil increases with increasing the Reynolds number in cavitating flow. When the cavitation number is decreased, it is found that two distinct cavity self-oscillation dynamics characterized by mainly responsible for the cavity breakdown. At 4 > σ/2α > 2.8, a low frequency shedding of cloud cavitation results in a strong oscillation in lift at a Strouhal number, based on chord length, of about 0.11. This frequency is relatively insensitive to changes in σ. As σ/2α < 2.8, cavity lengths exceed the foil chord, the growth breakdown cycle of the cavity is observed at a higher Strouhal number, of about 0.28.