Flow structure and cavitation evolution of submerged waterjet produced through different nozzles

The submerged waterjet was studied using flow visualization and numerical techniques. The proper orthogonal decomposition (POD) method was employed to analyze energy distribution and flow structures at different waterjet pressures. The effect of nozzle structure on cavitation was investigated. The results show that turbulent structures of the submerged waterjet are dominated by large-scale vortices, which exhibit an ordered coherent structure that evolves downstream with crossing, splitting, and reconnection behaviors. At low-order eigenmodes, large-scale flow structures exhibit a parallel and symmetrical distribution. As the waterjet pressure increases, high-energy large-scale flow structures remain relatively stable, and changes are evidenced in the flow structures associated with high-order eigenmodes. Meanwhile, the cavitation pattern transitions from dispersed cavitation bubbles to string cavitation and eventually to relatively stable cloud cavitation. The cavitator alone does not substantially enhance cavitation, and the introduction of a cavitator in conjunction with a spacer and a restraint pipe enables a significant enhancement of cavitation intensity.