In the previous study which was conducted by J. P. Franc et al., it was reported that on NACA16-012 hydrofoil at the angle of attack 4 degree, partial cavitation disappears although cavitation number is decreasing. We call this phenomenon "Disappearance phenomenon" and aim to clarify this mechanism. In the same previous study, it was also reported that at around 4 degree, reattachment of laminar separation leads transition to turbulence boundary layer and cavity cannot occur. In this study, in order to investigate the detail of boundary layer characteristic at the angle of attack where disappearance phenomenon occurred, we measured the pressure distribution on NACA16-012 hydrofoil and made boundary layer visible by oil flow method. In addition, fluid force was measured under the conditions from non-cavitation to super cavitation in order to estimate boundary layer characteristics during disappearance phenomenon. As the result, although the position of reattachment was different, reattachment of laminar separation described in previous study was confirmed and the lift during disappearance phenomenon was the almost same value as that of non-cavitation condition. From this result, it could be inferred that pressure distribution i.e. boundary layer characteristic during disappearance phenomenon was greatly different from that of non-cavitation condition.

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We propose a tangential blowing cylinder, a type of circulation control wing, to control the direction of a jet replacing a blade or a cascade. Flow characteristics including deflection are experimentally investigated. Specifically, visualization observations, velocity distribution measurements, and the effects of momentum ratio, injection angle, and location of the cylinder on the deflection angle of the jet are analyzed. The stalling at an angle-of-attack above 20°with a single blade impedes direction control for such large angles. However, the jet may be bent to approximately 90°by using the proposed tangential blowing cylinder. The optimal injection angle for controlling the jet direction and the unsteady characteristics downstream of the tangential blowing cylinder are also determined.

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