In the present paper, we present an experimental investigation of the onset and detachment of a leading edge cavitation over a 2-D and 3-D hydrofoils. An insight of the flow field in the vicinity of the main cavity detachment is reached with the help of a miniature sensor fitted in a NACA009 hydrofoil suction side close to the leading edge stagnation point. Owing to theses experiments, we have demonstrated how the water may withstand negative pressure as low as −0.8 bar without any visible cavitation. As soon as the leading edge cavitation takes place, the pressure upstream to the cavity detachment rises significantly but remains negative while the measured pressure in the cavity is almost equal to the vapor pressure. This result confirms the assumption already stated by former studies according to which the liquid is in tension just upstream to the detachment point. Furthermore, flow visualization clearly shows that a well developed leading edge cavitation turns into bubble cavitation in a continuous way when the surrounding pressure is gradually increased. Owing to those results, we have introduced a physical model of the cavitation detachment in which, no laminar separation of the boundary layer is required to ensure its mechanical equilibrium as already stated by former studies. The nuclei in the vicinity of the blade surface explode as they cross the liquid-vapor interface, which is not a material surface. The main cavity is thus continuously fed with exploding bubbles at its detachment location. The negative pressure measured upstream to the cavity detachment may thus be explained by the dynamic delay of exploding nuclei due to inertia.

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