Analysis of flow field characteristics and structural optimization of self-excited oscillating pulse jet nozzles

Oscillating jet technology has gained considerable attention due to its strong pulsation intensity and excellent hydrodynamic performance. In this study, large eddy simulation (LES) is employed to model the three-dimensional transient flow field of the oscillating nozzle, considering design variables, such as inlet diameter, outlet diameter, feedback channel width, and wall-attached angle. Single-factor response analysis indicates that adjusting the nozzle's geometric configuration can regulate the inlet jet morphology, expand the outlet disturbance range, and influence the return flow in the feedback channel as well as wall attachment inside the oscillation chamber. Using the Box–Behnken design and the response surface method (RSM), regression equations were established with pressure fluctuation average difference and average outlet pressure as objective functions to optimize the structural parameters. Fourier decomposition and multi-scale proper orthogonal decomposition (MPOD) analyses of the flow field reveal that the optimized self-excited oscillating pulse jet nozzle (O-ON) exhibits stronger jet intermittency, higher frequency amplitudes in the temporal coefficients, and more regular periodic outlet pressure pulsations. Aluminum block impact experiments further confirm that the O-ON nozzle produces a larger erosion area and stable pressure pulsations. This work provides guidance for optimizing the flow field performance of self-excited oscillating pulsed jets and offers a useful reference for structural design in applications, such as rock fragmentation, surface descaling, and fracturing drilling.