Direct Visualization of Laser-Driven Focusing Shock Waves

Cylindrically or spherically focusing shock waves have been of keen interest for the past several decades. In addition to fundamental study of materials under extreme conditions, cavitation, and sonoluminescence, focusing shock waves enable myriad applications including hypervelocity launchers, synthesis of new materials, production of high-temperature and high-density plasma fields, and a variety of medical therapies. Applications in controlled thermonuclear fusion and in the study of the conditions reached in laser fusion are also of current interest. Here we report on a method for direct real-time visualization and measurement of laser-driven shock generation, propagation, and 2D focusing in a sample. The 2D focusing of the shock front is the consequence of spatial shaping of the laser shock generation pulse into a ring pattern. A substantial increase of the pressure at the convergence of the acoustic shock front is observed experimentally and simulated numerically. Single-shot acquisitions using a streak camera reveal that at the convergence of the shock wave in liquid water the supersonic speed reaches Mach 6, corresponding to the multiple gigapascal pressure range 30 GPa

Rarefaction Waves and Bubbly Cavitation in Real Liquid

The paper presents the short review of two stages of cavitating liquid fracture at the explosive loading. The problems of the real liquid state (with view point of its inhomogeneity) and limit tensile stress, as well as the mechanics of the cavitation development excited by intense rarefaction waves and the dynamic feature of breaking of a spherical liquid drop under the action of ultra-short shock wave are considered

Hydrodynamics of Explosion: Experiments and Models

Hydronamics of Explosion presents the research results for the problems of underwater explosions and contains a detailed analysis of the structure and the parameters of the wave fields generated by explosions of cord and spiral charges, a description of the formation mechanisms for a wide range of cumulative flows at underwater explosions near the free surface, and the relevant mathematical models. Shock-wave transformation in bubbly liquids, shock-wave amplification due to collision and focusing, and the formation of bubble detonation waves in reactive bubbly liquids are studied in detail. Particular emphasis is placed on the investigation of wave processes in cavitating liquids, which incorporates the concepts of the strength of real liquids containing natural microinhomogeneities, the relaxation of tensile stress, and the cavitation fracture of a liquid as the inversion of its two-phase state under impulsive (explosive) loading. The problems are classed among essentially nonlinear processes that occur under shock loading of liquids and may be of interest to researchers in physical acoustics, mechanics of multiphase media, shock-wave processes in condensed media, explosive hydroacoustics, and cumulation

STRUCTURE OF PERIODICAL DISTURBANCES IN REAL LIQUID

Dans cet article, on étudie les ondes supersoniques et la cavitation qui prennent naissance dans un liquide contenant du gaz libre sous forme de bulles. L'onde de pression est produite par un piston qui oscille périodiquement. Les calculs numériques sont conduits, dans le cadre du problème à une dimension, en s'appuyant sur le modèle diphasique hors équilibre. Initialement, la teneur en gaz est K0 = 10-8 et le rayon des bulles R0 = 10-3 cm. Le piston oscille avec une fréquence qui peut varier de 1 à 200 kHz ; l'amplitude de son déplacement peut prendre deux valeurs, qui correspondent pour la pression (dans un liquide ne contenant pas de gaz) à des amplitudes de 9 à 49 atm. On montre que l'amplitude, la durée et la forme de l'onde de pression dépendent fortement de la fréquence excitatrice. C'est ainsi que la diminution de cette fréquence provoque, pour l'onde de pression, une augmentation de la fréquence, une diminution de l'amplitude et une profonde modification de la forme par rapport au modèle monophasique. Les calculs ne sont pas conduits jusqu'au moment de l'implosion.Within the framework of the nonequilibrium two-phase model the structure of supersonic waves and the cavitation development are investigated in a real liquid containing a free gas as cavitation bubbles. The calculation were carried out at the initial volumetric gas concentration K0 = 10-8, the gas bubble radius R0 = 10-3 cm and the oscillation frequency of the piston ranged from 1 to 200 kc