EXPERIMENTAL INVESTIGATION OF THE VIBRATION CHARACTERISTICS OF HYDROFOIL IN CAVITATING FLOW

Cavitation is a kind of complex and unsteady hydrodynamics phenomenon occurred in hydraulic machinery. The cavity shedding leads to structure vibration which a ects the e ciency, noise and safety of hydraulic machinery, so it is important to study the structure vibration in cavitating flow. The characteristics of the cavity shape around a NACA66 hydrofoil and the vibration response are analyzed experimentally. A high-speed video camera is used to visualize the unsteady cavitating flow patterns and a laser doppler vibration meter is used to measure the vibration velocity. The highspeed video camera and the laser doppler vibration meter can be triggered synchronously by a synchronization system. The characteristics of cavity shape and vibration in di erent cavitation stages are analyzed both in time field and frequency field. Synchronous results of cloud cavitation are studied. It is found that as the cavitation number decreases, four stages of cavitation are visualized in which are non-cavitation, cavitation inception, sheet cavitation and cloud cavitation. The vibration amplitude of the hydrofoil increases as the cavitation number decreases. Cavities shedding leads to vibrations whose dominant frequencies are same with the frequencies of cavities shedding at sheet cavitation and cloud cavitation stages. At the cloud cavitation stage, the vibration is high-frequency and low-amplitude when the attached cavity develops. At the stages of cavity pulsation and cavity shedding, the vibration is low-frequency and high-amplitude.