Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 08, 2021 - November 10, 2021
Generally, cavitation develops as the cavitation number decreases. However, on NACA16-012 hydrofoil, once occurred cavitation disappears despite of in low cavitation number condition. This phenomenon was called as cavitation disappearance phenomenon. In previous study, Franc and Michel reported that cavitation disappears at the angle of attack where the laminar separation point and transition region move from the rear to the front of the hydrofoil. Between two consecutive turbulent spots, the boundary layer is laminar, and a sheet cavity can develop locally for a short time, before being swept out by the next turbulent spot. Our research group confirmed that cavitation disappearance phenomenon was unique to NACA16-012 hydrofoil, the pressure distribution was different under disappearance condition from under non-cavitation condition despite of the same single-phase flow, and the short bubble was instability at the angle of attack where cavitation disappearance phenomenon occurs. It was considered that the boundary layer changed to one which cavitation did not occur due to some effect. In this study, for the purpose of investigating the relationship between cavitation disappearance phenomenon and the boundary layer, the boundary layer was experimentally investigated. As the experimental apparatus, low-turbulence heat-transfer wind tunnel installed at Tohoku University was used. Normally, the cavitation tunnel should be used, however the size of hydrofoil was too small to accurate measure, therefore the wind tunnel was used. NACA16-012 airfoil with the chord length of 200 mm and the span length of 1400 mm was used. The experimental conditions were set to mainstream velocity of 36 m/s, temperature of 16 ℃. Oil film method was used to visualize the boundary layer. As the results, the angle of attack where cavitation disappearance phenomenon occurs corresponds to onset of the short bubble. This tendency is consistent with the results of Franc and Michel in 1985. Therefore, it was suggested that onset of the short bubble related to cavitation disappearance phenomenon.
