International audienceWe conducted a series of shock tube experiments to study the influence of a cloud of water droplets on the propagation of a planar shock wave. In a vertically oriented shock tube, the cloud of droplets was released downwards into the air at atmospheric pressure while the shock wave propagated upwards. Two shock wave Mach numbers, 1.3 and 1.5, and three different heights of clouds, 150 mm, 400 mm, and 700 mm, were tested with an air-water volume fraction and a droplet diameter fixed at 1.2% and 500 mu m, respectively. From high-speed visualization and pressure measurements, we analyzed the effect of water clouds on the propagation of the shock wave. It was shown that the pressure histories recorded in the two-phase gas-liquid mixture are different from those previously obtained in the gas-solid case. This different behavior is attributed to the process of atomization of the droplets, which is absent in the gas-solid medium. Finally, it was observed that the shock wave attenuation was dependent on the exchange surface crossed by the shock combined with the breakup criterion. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3657083

International audienceCompressible granular materials are involved in many applications, some of them being related to energetic porous media. Gas permeation effects are important during their compaction stage, as well as their eventual chemical decomposition. Also, many situations involve porous media separated from pure fluids through two-phase interfaces. It is thus important to develop theoretical and numerical formulations to deal with granular materials in the presence of both two-phase interfaces and gas permeation effects. Similar topic was addressed for fluid mixtures and interfaces with the Discrete Equations Method (DEM) [R. Abgrall and R. Saurel, ``Discrete equations for physical and numerical compressible multiphase mixtures,''J. Comput. Phys. 186 (2), 361-396 (2003)] but it seemed impossible to extend this approach to granular media as intergranular stress [K. K. Kuo, V. Yang, and B. B. Moore, ``Intragranular stress, particle-wall friction and speed of sound in granular propellant beds,'' J. Ballist. 4 (1), 697-730 (1980)] and associated configuration energy [J. B. Bdzil, R. Menikoff, S. F. Son, A. K. Kapila, and D. S. Stewart, `` Two-phase modeling of deflagration-to-detonation transition in granular materials: A critical examination of modeling issues,'' Phys. Fluids 11, 378 (1999)] were present with significant effects. An approach to deal with fluid-porous media interfaces was derived in Saurel et al. [''Modelling dynamic and irreversible powder compaction,'' J. Fluid Mech. 664, 348-396 (2010)] but its validity was restricted to weak velocity disequilibrium only. Thanks to a deeper analysis, the DEM is successfully extended to granular media modelling in the present paper. It results in an enhanced version of the Baer and Nunziato [''A two-phase mixture theory for the deflagration-to-detonation transition (DDT) in reactive granular materials,'' Int. J. Multiphase Flow 12 (6), 861-889 (1986)] model as symmetry of the formulation is now preserved. Several computational examples are shown to validate and illustrate method's capabilities. (C) 2014 AIP Publishing LLC

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This paper presents a method that allows very accurate measurements for a full characterization of shaped charge jets.A double visualization of the jets is achieved by means of both a modified high speed camera CORDIN i Double Orthogonal Synchro Streak Technique (DOSST) configuration and a classical Double X.Rays Technique (DXRT).The interests of this method are twofold: -Firstly, the DOSST and the DXRT complement each other. Because of the high precision of the system, DOSST allows to obtain very accurate space-time data. But some fragments can be hidden either at the jet tip by shock waves or at the rear of the jet by some detonation products. With DXRT, all fragments are visible on the X-ray photograph.-Secondly, the validity of the results can be controlled by comparing, on the same experiment, the X-ray data with the camera data.For each fragment, the raw data (space-time position, length and area) is semi-automatically determined by an image processing system developed at the Centre Technique des Systèmes Navals (CTSN). Then, all the usual characteristics of the jet are calculated using appropriate algorithms.The experimental methodology, the data processing and the results obtained for various shaped charges are detailed. Values obtained by the high speed camera and the X-ray flashes are compared. Finally, comparisons between the calculated values and the experimental observations, like impact locations on the witness plates, are also made.