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Abstract

Experiences have shown that creating a super-cavitating flows over underwater projectiles can significantly reduce their drag forces and change their dynamical behaviors. So the extended issues of this problem have been studied by researchers in the recent decades. In this paper, the geometrical characteristics of super-cavities, developed downstream of three conical cavitator with cone angles of 30°, 45° and 60°, are studied. A semi open-loop water tunnel with maximum flow velocity of 38 m/s is utilized. The measurements are done for both cases of ventilated or air-injected and natural cavitation in a range of 0.34 ≦ σv ≦ 0.36. Validating of setup and measurements is done by comparison of present results with experimental data of a circular disk cavitator reported in the literature. Both the maximum diameter and the length of the cavities are determined from the relevant photos captured by a high speed camera. Also, to trace the pressure variations, the sensors which are located behind the cavitator, are used for determining the transient length of the cavity. Effects of important parameters such as the cavitation number, upstream flow velocity and cone angle of cavitators on the drag coefficients as well as cavity shapes and relevant dimensions are studied. The results also show that the most effective parameter on the drag coefficient is the cone angle of cavitators. In ventilated cases, reduction in drag coefficient is more sensitive to the amount of air-injection than the increasing of velocity. Also the measurements show that the cavity length increases dramatically as the supercavitation transforms from the natural to ventilated regime.

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