Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 07, 2019 - November 08, 2019
Under the specific angle of attack on NACA16-012 hydrofoil, generated cavitation suddenly disappears even in low cavitation number, in which cavitation is normally generated. This cavitation disappearance phenomenon was confirmed by previous research to be unique to NACA16-012 hydrofoil. It was experimentally confirmed that this phenomenon occurred when the sheet cavity generated on the hydrofoil was periodically broken and the cloud cavity was released. In this study, the break-off frequency before and after cavitation disappearance phenomenon was measured experimentally. NACA16-012 with the cord length of 30 mm and high-temperature and high-pressure water tunnel installed at Institute of Fluid Science, Tohoku University were used. Since the compressor and vacuum pump were connected to this tunnel, the pressure can be controlled independently of the flow velocity. The experimental conditions were flow rate of 13.4 m/s, water temperature of 30 ℃ and dissolved oxygen of about 30 %. Under these conditions, cavitation disappearance phenomenon was confirmed at angles of attack of 6° and 7°. The fluctuation of pressure was measured with a pressure transducer 80 mm downstream from the center of the hydrofoil and the characteristics frequency was evaluated by the frequency analysis. In general, the break-off frequency of cloud cavity releasing tends to decrease with decreasing cavitation number. However, NACA16-012 hydrofoil showed different results. The peak of the break-off frequency increased to a certain frequency when the cavitation number decreased. In addition, no strong peaks were observed before and after this break-off frequency, it is assumed that the frequencies before and after the break-off frequency were related to the cavitation disappearance phenomenon.
