Splashing and sealing of an ejecta sheet induced by a cavitation bubble close to a water surface

An ejecta sheet is commonly formed when a cavitation bubble bursts into the air, creating an open cavity. The evolution of the sheet has been studied independently, with limited focus on the interaction between the ejecta sheet and the cavity. This study offers insights into the splashing and sealing of a laser-induced ejecta sheet. An object-distance compensation method is developed to capture clear images of the phenomena both above and below the water surface simultaneously. The ejecta sheet exhibits two patterns: an open splash and a sealed splash. In the case of an open splash, the cavity seals quasistatically, whereas in the case of a sealed splash, the cavity type transitions from shallow sealing to surface sealing as the dimensionless standoff distance γ increases. An axisymmetric model is proposed for analyzing how the ejecta sheet evolves during the sealing process. Since the sealing process is dominated by suction pressure resulting from rapid expansion of the cavity, we obtain the cross-sectional area As of the ejecta sheet as a function of the rates of change of the bubble volume (V̇b) and the sheet cross-sectional area (Ȧinn), and this function is shown to be independent of time. Remarkably, as γ increases, As decreases and increases in the regimes of shallow sealing and surface sealing, respectively. This tendency is induced by the significant difference in V̇b due to the initial state of the cavity. Our findings offer a new understanding of the dynamics of laser-induced ejecta sheets.