Cloud cavitation and flow field characteristics in sudden change channel

In this paper, the Delayed Detached-Eddy Simulation (DDES) model is used to simulate the cloud cavitation process and the flow field distribution characteristics in the three-dimensional cavitating chamber with a sudden change channel. The effect of cavitation evolution on the flow field is investigated by the change of vacuole volume fraction and the distribution of physical quantities in the flow field. And the Q criterion is introduced to identify the vortex structure and its variation. The results show that the evolution of cavitation presents periodic characteristics, but in a period, the flow field distribution, vortex structure, and vortex intensity under different cavitation states are different. In the stage of bubble growth, falling off, bubble cluster breaking, and separation, the vortex size is large and the vortex intensity is high, making the flow field show drastic fluctuations. However, in the stage of bubble mass integration, the flow field fluctuation is relatively weak, and the pressure fluctuation law is consistent with the bubble shedding frequency. In addition, the Q criterion indicates that the high-strength vortices are mainly concentrated in the throat, as the degree of cavitation increases, vortex breakage is intensified and vortices are not obvious in the flow field.