Outlet tube effects on cavitation cloud dynamics and erosion in self-excited waterjets

Using high-speed imaging and three-dimensional surface morphology analysis, we examined the cavitation cloud dynamics and erosion characteristics of self-excited pulsating cavitating waterjets. Erosion experiments on aluminum specimens were conducted to evaluate the influence of varying outlet tube diameters and lengths on the waterjet’s performance. Mass loss measurements revealed that the erosion capability increased approximately threefold under the optimal outlet tube configuration. Proper Orthogonal Decomposition (POD) of high-speed snapshots identified distinct primary and secondary shedding modes driven by passive acoustic excitation. The presence of an outlet tube was found to enhance the volume and development of the primary cavitation cloud while facilitating the merging of secondary and primary modes. This mode-specific structural evolution leads to a synergistic amplification of cavitation cloud intensity, which governs the enhancement of erosion capacity.