Experimental study of inception cavitation around axisymmetric bodies with different headforms

A high-speed video camera was used to observe the process and structure of cavitation inception, flow characteristics and effects of headforms around two axisymmetric bodies with blunt and cone-shaped respectively. A particle image velocimetry (PIV) system was employed to measure the velocity and vorticity fields. The results show that the shape of headform has an effect on inception cavitation number and cavity shapes. In this work, the inception cavitation numbers of the blunt body and the fastigiate one are 1.2 and 0.9 respectively. Traveling bubbles with hairpin type at inception cavitation are incurred in the region downstream from the corner and the cavities are detached from the surface of bodies. Compared with the cone-shaped body, the bigger traveling bubbles forming around the blunt body are farther from the shoulder and body surface. In addition, the flow field shows inception cavitation is related to vortex intensity of the flow around heads. Compared to the cone-shaped body with the same value of Re, the scale of detached vortex around the blunt body is bigger, shear layer is farther from the body surface, and the area of high vorticity is larger and farther from the body surface. All of these probably cause the different characteristics of inception cavitation of the two bodies.