Study on the cavitation erosion of a single bubble collapse near a rigid wall based on chronoamperometry

Cavitation is indeed a significant phenomenon in fluid dynamics, involving the formation, growth, and eventual collapse of vapor-filled bubbles in a liquid. This process can lead to various effects, particularly when bubbles collapse near a rigid wall, resulting in cavitation erosion. In this study, the dynamic behaviors of a single cavitation bubble collapsing near a rigid wall, focusing on varying dimensionless bubble-wall stand-off distances (γ) and the effects of dimensionless eccentricity (ε) were investigated. This study explored the pulsating evolution of a single cavitation bubble through high-speed photography, utilizing chronoamperometry combined with morphological analysis to characterize cavitation erosion damage. The results showed that: (1) At the dimensionless distance γ of 0.1 between the cavitation bubble and the wall, the peak current reached its maximum. This indicated that cavitation erosion was the most severe at this proximity. Both the high-velocity micro-jet generated during the first collapse of the bubble and the crushing flow generated during the asymmetric collapse of the ring vortex in the second collapse of the bubble contribute to cavitation erosion, with their damage effects being comparable. (2) When the dimensionless distance γ increased to 1.3, serious cavitation erosion was observed again, primarily caused by the collapse of the ring vortex. In this scenario, the contribution of micro-jets was minimal, indicating a shift in the erosion mechanism as the bubble was further from the wall. (3) At a dimensionless distance of 0.1, the material surface showed a centrally depressed area characterized by dense pits arranged in a ring-like distribution. This reflected the intense local impacts from the bubble collapse. At a distance of 1.3, the damage morphology was different, featuring only a ring-like distribution of dense pits with a flatter center. This change suggested that the collapse dynamics and resulting jet interactions vary significantly with distance. The morphological observations aligned with the cavitation mechanisms identified through chronoamperometry, reinforcing the relationship between bubble dynamics, erosion intensity, and the resultant material damage.