Simulation analysis of self-excited oscillating water jet with petal-shaped nozzle under confining pressure

The self-excited oscillating water jet is widely used in ocean engineering. Its effectiveness stems from the impact of cavitation collapse driven by periodic pressure pulsations. This study investigated the flow field evolution and vortex stretching mechanisms of self-excited oscillating water jets using large eddy simulation. The combined effects of petal-shaped nozzle structure and confining pressure were considered. Three confining pressures (0.1, 0.3, and 0.5 MPa) were considered. Flow field visualization combined with dynamic mode decomposition (DMD) was employed to investigate the flow characteristics of the jet. The simulation results demonstrate that elevated confining pressure enhances vortex compression more significantly than vortex stretching for the four-petaled nozzle. For the circular nozzle, vortex stretching peaks at an intermediate pressure and weakens at higher pressures. Nozzles with lower degrees of rotational symmetry are dominated by multi-order low-frequency modes. Increasing the confining pressure splits the large-scale vortex structure, thereby weakening the jet intensity while improving the uniformity of the vortex field. The results provide a basis for selecting nozzle geometries and operating conditions under the investigated confining pressures.