Abstract: The erosion pattern of self-excited cavitating waterjet is the most intuitive characteristic of operation. However, its evolution mechanism is not yet clear, which limits the active control of the pattern and the efficient application of waterjet. Firstly, erosion experiments of self-excited cavitating waterjet were carried out to elucidate the evolution of erosion pattern as cavitation number and standoff distance changed. The instantaneous morphological characteristics of the cavitation cloud under different erosion patterns were obtained by visualization experiments based on a high-speed camera. The statistical regularity of bubble collapse was obtained by orthogonal modal decomposition. Meanwhile, combined with the computational fluid dynamics simulation method based on transient large eddy simulation, the fluid dynamic characteristics under typical erosion patterns were obtained to explore and clarify the erosion patterns’ formation mechanism. The research results show that under different cavitation numbers, with the increase of standoff distance, three representative erosion patterns, A, B and C, appear, in which erosion pattern A is composed of erosion ring 1 and larger erosion ring 2, erosion pattern B contains only erosion ring 1, erosion pattern C mainly comprises erosion ring 1 and smaller erosion ring 3. Ring 1 as the primary ring occurs in all the patterns, which possesses the highest erosive power. The transfer mode between different erosion pattern is related to cavitation number. The formation mechanisms of three erosion patterns are as follows: when the standoff distance is short, ring 1 of pattern A is eroded by the collapsing of the cavitation cloud that appears in the waterjet’s shear layer, and ring 2 is caused by the secondary cavitation cloud incepted in vortex ring near the wall. When the standoff distance is large, erosion pattern B contains only ring 1, mainly caused by the collapse of the primary cavitation cloud in the waterjet’s shear layer. Under a specific cavitation number and standoff distance, rings 1 and 3 in erosion pattern C are generated by the alternating shedding and colliding of the cavitating waterjet’s primary and secondary cavitation clouds.

Key words: self-excited waterjet, cavitating waterjet, erosion pattern, cavitation cloud, fluid dynamics