Analysis of the vortex-pressure coupling mechanism in cavitation dynamics for self-excited oscillation nozzles and its structural optimization

This study investigates cavitation dynamics in a self-excited oscillation nozzle (SEON) under gravitational influence using high-speed imaging, computational fluid dynamics (CFD) simulations, Proper Orthogonal Decomposition (POD), wavelet analysis, and multi-objective optimization with Dynamic Adaptive NSGA-II (DANSGA-II). High-speed imaging displays the formation, detachment, and collapse of cavitation cloud. CFD simulations reveal the internal flow field and vapor distribution, clarifying cavitation evolution in the SEON chamber. POD and wavelet analyses demonstrate a nonlinear relationship between cavitation behavior and inlet pressure, with peak performance at 1.5 MPa. A novel vortex-pressure pulsation coupling mechanism was proposed to explain cavitation cloud development. This mechanism guided structural optimization by selecting chamber length (L), impingement wall angle (α), and outlet contraction ratio (d₂/D) as design variables. Multi-objective optimization using DANSGA-II produced optimal nozzle designs. For example, in Case 1 (L = 10.1 mm, α = 103°, d₂/D = 0.1881), the mean vapor volume fraction increased by 59.18 %, and turbulent kinetic energy rose by 32.32 %. Methylene blue degradation experiments showed a 15.88 % removal efficiency after 120 minutes, improving 77.8 % over the baseline. This study investigated a vortex-pressure coupling mechanism through integrated visualization and simulation techniques, thereby facilitating the structural optimization of SEONs and enhancing cavitation performance. The findings provide both theoretical insights and practical guidance for the design and application of SEONs in industrial cleaning and wastewater treatment processes.