Flow field characteristics and three-dimensional coherent structures of free and impinging cavitating water jets: Effects of nozzle configuration
Runyu Zhu, Wenqian Xi, Haitao Zhu, Xiaohui Zhang, Shize Pan, Bo Li, Zhongliang Xie
Abstract
In engineering applications leveraging the erosive capabilities of submerged cavitating jets, impinging jets are prevalent, and optimizing nozzle configuration can enhance cavitation-induced erosion. This study investigates the effects of nozzle configuration on flow structures and erosion intensity in both free and impinging submerged cavitating jets. Two nozzle configurations are analyzed: one with a cylindrical expansion section and one without. High-speed visualization, erosion testing, and numerical simulations with the stress-blended eddy simulation turbulence model and Schnerr–Sauer cavitation model are integrated to resolve cavitation dynamics. Proper orthogonal decomposition (POD) is further used to analyze the three-dimensional coherent structures. In results, the expansion section enhances both cavitation and erosive intensity, producing periodic cloud shedding through generating upstream-directed reentrant motion that is accompanied by vortex fragmentation. Impinging jets from a nozzle with an expansion section produce structured cavitation cloud collapse with extended high-pressure regions. Wall impingement induces axial-to-radial vortex reorientation, reducing vorticity density in the expansion region. POD analysis indicates that the expansion section concentrates energy in low-order modes, reflecting stronger large-scale fluctuations, while spectral entropy highlights the frequency modulation effect of the expansion section. Moreover, wall constraint in impinging jets promotes small-scale fluctuations.