A novel ejector-type nozzle for enhanced erosion performance of submerged cavitating jets: Insights from high-speed visualization

Submerged cavitating jets have attracted extensive attention in engineering applications due to their exceptional erosion capability. Optimizing nozzle configuration substantially enhances cavitation-induced erosion intensity without increasing injection power. Inspired by the design and working principle of jet pumps, this study proposes a novel ejector-type cavitation nozzle aimed at further enhancing cavitation erosion performance. This study employs impingement tests and high-speed imaging to analyze the erosion characteristics of three ejector-type nozzles, three conical expansion-type nozzles, and a cylindrical expansion-type nozzle at various standoff distances. Furthermore, spectral analysis and spectral proper orthogonal decomposition (SPOD) are utilized to investigate the frequency distribution and coherent structures of the cavitation clouds. The results indicate that the ejector-type nozzle induces an erosion intensity 192.83% higher than the conical expansion-type nozzle, which itself induces 2.93 times the erosion of the cylindrical expansion-type nozzle. The ejector-type nozzle promotes the complete initiation and development of cavitation clouds and increases the kinetic energy of the jet core, thereby extending the optimal standoff distance and the axial and radial impingement range of the kinetic energy. Additionally, the nozzle exhibits superior frequency modulation capability, with cavitation shedding behavior displaying notable periodicity and higher energy concentration. SPOD analysis shows that the coherent structure of the cavitation cloud induced by the ejector-type nozzle extends farther axially and maintains a relatively intact shape upon target impingement, confirming its improved energy transfer and sustainability.