Recent Advances in Experimental and Numerical Studies on Cloud and Erosion Behaviors in Cavitating Jets

Recent advances in experimental techniques for visualizing cloud behavior, pit formation, and erosion in cavitating jets have been reviewed. To characterize the erosion behavior of cavitating jets and clarify their erosion mechanisms, various experimental techniques—such as high-speed imaging, frame difference method, proper orthogonal decomposition (POD) analysis, pit sensors, polyvinylidene fluoride (PVDF) sensors, laser schlieren imaging, and cross schlieren imaging—have been developed. Experimental results demonstrated that the erosion mechanism of cavitating jets is highly correlated with periodic cloud behaviors, including the growth, shrinkage, and collapse, which generate impulsive pressure on the wall material. This pressure initiates random pits on the wall surface and is associated with the generation of microjets caused by the reentrant-jet mechanism during cloud collapse near the wall. Several shockwaves were generated at peak impulsive pressures when the cavitation cloud collapsed, and a microjet was formed. Some of these experimental findings were successfully reproduced in recent numerical studies; however, further numerical modeling of erosion behavior in cavitating jets is still needed. Furthermore, the behavior of cavitating jets on rough walls requires future study, as the erosion rate is significantly higher than that on smooth walls.