Submerged cavitation water jet, with intensive cavitation erosion ability, has been extensively applied for various engineering purposes such as petroleum well drilling and reservoir stimulation. The dynamics of cavitation cloud are closely related to the erosion process of cavitation jet. In this paper, high-speed photography is utilized to visualize the cavitation jet. The dynamic features of cavitation cloud are illustrated using Frame Difference Method; the mechanism of periodic cavitation cloud shedding is discussed; and for the first time, the influences of variable type (the length, area, width of cavitation cloud, the gray level of points in jet center line and the average gray level) and variable position on determining the shedding frequency of cavitation cloud are clarified, based on which the optimal method to decide the shedding frequency is derived. The results show that cavitation cloud in submerged cavitation has evident periodicity. One cycle contains incubation, developing, shedding and collapse phases. The periodic shedding of cavitation cloud seems to be closely related to the shedding of vortex in the shear layer, the nozzle structure and the variety of nozzle open area as a result of the cavitation appearance and its ‘chock effect’. Average gray level is believed to be the optimal viable for determining the shedding frequency of cavitation cloud. Under the experimental conditions in this paper, the shedding frequency of cavitation cloud is decided to be 1?350 Hz. The region where shedding frequency is stable ranges from 17.6 mm to 28.16 mm from the nozzle outlet. This paper provides an important supplement for understanding the dynamics of cavitation cloud in submerged cavitation jet and builds the foundation of optimizing the nozzle geometry based on shedding frequency.
