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The paper is devoted to the investigation of a dynamics of state and structure of compressed magma flow saturated by gas and microcrystallites which is characterized by phase transitions, diffusive processes, by increase of a magma viscosity magnitude by the orders and bubbly cavitation development behind the decompression wave front formed in the result of volcanic channel depressurization. The multi-phase mathematical model, which includes well-known conservation laws for mean pressure, mass velocity, and density as well as the system of the kinetic equations describing the physical processes that occur in a compressed magma during its explosive decompression, is considered. The results of numerical analysis show that the processes of a magma saturation by cavitation nuclei as their density magnitude increases by a few orders lead to the formation of separate zone with anomalously high values of the flow parameters. As it has turned out the abnormal zone is located in the vicinity of a free surface of a cavitating magma column. The mechanism of its formation is determined by diffusion flows redistribution as the nuclei density increases as well as by the change of the distribution character of main flow parameters in the abnormal zone from a gradual to an abrupt increase of their values on the lower zone bound. Note, the mass velocity jump by the order magnitude relatively main flow allows to conclude that the flow disintegration on the lower bound of the zone is quite probable. [Supp. RAS Presidium Program, Project 2.6].

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.]

The evolution of bubble cavitation behind the front of a converging cylindrical rarefaction wave in distilled water containing micro inhomogeneities is investigated numerically within the framework IKvanW mathematical model. The dynamics of the cavitation zone state is considered in a one-dimensional formulation with cylindrical symmetry. A thin liquid layer bounded by the free surface is loaded by a shock wave generated by a piston coaxial the axis of symmetry. As a result of shock wave reflection from free surface, a rarefaction wave converging toward the axis of symmetry is formed. The influence of the initial size of microbubbles, gas phase concentration, and parameters of shock wave loading on the dynamics offormation of the cavitation zone and its growth in the course of rarefaction wave focusing is analyzed.