Flow field characterization of cavitation water jets applied to concave, plane, and convex surfaces

The cavitation cloud is a significant guide for the assessment of the non-constant behavior of cavitation water jets. Nevertheless, the mechanism by which the cavitation cloud evolves when a cavitation jet is applied to different target surface shapes remains unclear. In order to investigate the evolution and collapse mechanism of cavitation clouds on different target surface shapes, this study employs a high-speed visualization system to observe the behavior of cavitation water jets impinging on concave, planar, and convex surfaces. By analyzing the shedding behavior of the cavitation cloud and the morphological evolution on the target surface, the influence of the target surface shape on the cavitation cloud is explored, and the law of the morphological evolution of the cavitation cloud is obtained. The frequency of cavitation ring formation is approximately 0.7 ms when the cavitation jet strikes concave surfaces and approximately 0.8 ms when the cavitation jet hits planar and convex surfaces. Furthermore, the variation of the cavitation structure is illustrated by proper order decomposition (POD) and Dynamic Mode Decomposition (DMD) analyses, which demonstrate that the concave targets are prone to triggering high-frequency turbulence and the formation of unstable vortex structures. In contrast, plane and convex surfaces tend to stabilize the flow, although they also exhibit significant instability in higher-order modes. The behavior of cavitation flows upon impact with different target surfaces is simulated using the Large Eddy Simulation (LES) turbulence model in conjunction with the Zwart–Gerber–Belamri (ZGB) cavitation model. The results demonstrate that upon impacting the concave surface, the jet generates a series of reflows in the central region. These reflows not only result in the formation of vortices but also exert a significant influence on the cavitation cloud, accelerating its discharging frequency. In contrast, the cavitation jet impingement planes and convex surfaces exhibit less sensitivity to the refluxes. The results of this study provide technical support for the application of cavitation jets on concave surfaces (cleaning of tube, casing), flat surfaces (shot peening), and convex surfaces (cleaning of submarine pipelines) and contribute to a broader understanding of the erosion mechanism of cavitation jets.