The kinetic mechanism of vortex-cavitation interaction in dual-chamber self-excited oscillation waterjets

To explore the kinetic mechanism of vortex-cavitation in self-excited oscillation waterjets, large Eddy simulation was employed to simulate waterjets generated by a Helmholtz nozzle, an organ pipe nozzle, and a dual-chamber nozzle. The deconstruction from vortex energy to cavitation generation mechanisms was accomplished through proper orthogonal decomposition. The vorticity transport equation was used to investigate the relationship between the cavitation cloud in the cleavage state and each of the terms after the corresponding vortex decomposition. The results emphasize the importance of diffusion lip and downstream nozzle length in enhancing the jet capability of the dual-chamber nozzle. Furthermore, the excitation generated by the fluid after modulation through the Organ pipe nozzle significantly enhances the shear capacity of the dual-chamber nozzle jet. The interaction process between vortex-walls in the dual-chamber nozzle is described, with a particular focus on explaining the principle of self-excited oscillation generated by the organ pipe nozzle. The direction of shear vortex rotation represents the area of expansion in the cavitation cloud cluster. The end of the cavitation cloud exchanges energy with the surrounding water, and the expansion and disappearance of the cavitation cloud are directly related to the velocity state of the jet. The waterjets produced by the three types of nozzles have different shear forms to generate cavitation. Compared with waterjets from Helmholtz and organ pipe nozzles, the vapor volume fraction at the center of the dual-chamber nozzle jet increases by 56.3% and 77.6%, respectively, at a distance of 15 times the inlet diameter of the downstream chamber from the outlet.