Empty cavity in a cavitating liquid: Features of flow structure

Abstract

Problem of empty cavity dynamics in a two-phase medium is considered. The initial equilibrium state of “cavity-medium” system is disturbed when pressure inside cavity falls abruptly up to 0. Rarefaction wave arising on an interface initiates a cavitation development. Two-phase mathematical model is applied to investigate the medium state dynamics. The medium parameters correspond to a distilled water state: microbubbles, 1.5 μm, their density 106 cm-3, and gas concentration, about 10-5. The numerical analysis has shown that interface “cavity-medium” becomes a cavitating spherical layer. The concluding process of cavity collapse can be characterized by two stages. First, the interface as a spherical layer in a result of its cumulation is transformed into a spherical bubbly cluster with 1 mm radius. Cluster contains 2.5·105 см-3 microbubbles with 40 μm radii. Gas concentration is distributed from 20%,cluster center, up to 1% on its surface. Second, the cumulation of flow on the spherical bubbly cluster will determine a level of internal energy of compressed bubbly cluster and its further dynamics. The similar phenomenon was found in the experiments on the development, structure, and collapse of a rupture forming in cavitating layer of distilled water at its shock-wave loading. The analysis of experimental data has shown that a rupture in the cavitating layer is the cavity with interface as thin layer of cavitating liquid and its collapse tends to the bubbly cluster formation. [Support RFBR, grant 15-05-03336.]