Abstract: To address the dynamic characteristics of cavitating flows, the unsteady characteristics of cavitating flows around a Clark-y hydrofoil are investigated experimentally. The experiments are carried out in a rectangular test section of a closed cavitation tunnel. A high-speed video camera is used to visualize the unsteady cavitating flow patterns. The observition results are analysed by using a home-developed software. The drag and lift under different cavitation conditions are measured. The spectral analysis of the measured date is conducted. It is found that the dynamic characteristic of the cavitation varies considerably with the changes of the cavitation number. Two stages of the development of unsteady cavitation are observed. When , the average non-dimensional length of the cavities is less than 0.7, while the Strouhal number, based on chord length, corresponding to the peak of the power spectral densities of the cavity length and lift, is above 0.3. When , the non-dimensional cavity length is in the range of . A low frequency shedding of cloud cavitation results in a strong oscillation in lift at the Strouhal number of about 0.18. This frequency is relatively insensitive to changes in cavitation number.

Key words: Cavitating flow, Shedding frequency, Spectral analysis, Unsteady fluid dynamics