Experimental investigation of unsteady cavitating flows around axisymmetric bodies with different headforms

A high-speed video camera was used to observe the process of cavity development, flow characteristics and effects of headforms around two axisymmetric bodies with blunt and 45° half cone angle shaped headforms respectively, with the circumstances of different cavitation numbers. A particle image velocimetry (PIV) system was employed to measure the velocity, vorticity and turbulent energy fields. The results show that at a given cavitation number, the maximum scale of the cavity around the blunt body is significantly bigger than that of the cone-shaped body. And as the cavitation number decreases, the cavities of the blunt body develop faster as compared with the cone-shaped body. It has been found that the process of cavity development around the blunt body represents a number of large cavity vortexes conjunct with each other, then they shed and disappear together with obvious unsteady characters, while there is a small scale cavity behaving around the cone-shaped body. In addition, from the flow field it appears that in the cavity area the flow speed is low and the instability is pronounced meanwhile the velocity distributing trends uniformly. What's more, with the cavitation number decreasing, the fluctuations in the cavities become fairly pronounced which induces the turbulent instability and causes the area with high turbulent energy to spread and broaden.