Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session L4: Post Shock Turbulence I |
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Chair: Sunil Dwendi, University of Florida Room: Renaissance Ballroom C |
Wednesday, June 29, 2011 9:15AM - 9:30AM |
L4.00001: Modeling Turbulent Mixing Baolian Cheng, James Glimm, David Sharp Fluid mixing is an important phenomenon in many physical applications from supernova explosions to genetic structure formations. Moving interfaces between distinct fluids in a multi-fluid system are often unstable. Small perturbations at such interfaces grow as a result of nonlinear hydrodynamic processes, and evolve into turbulent mixing regions. Three major types of hydrodynamic instability play an important role in mix processes: (1) the Rayleigh-Taylor instability, occurring when a fluid pushes another fluid of higher density; (2) the Richtmyer-Meshkov instability, which takes place when a shock wave accelerates a perturbed interface between two fluids of different densities; and (3) the Kelvin-Helmholtz instability, which arises when a nonzero velocity discontinuity exists between the two fluids. In this work, we present theoretical models to predict the mixing growth rates and numerical simulations for the chaotic mixing fluids. Our results are in good agreement with experiments. [Preview Abstract] |
Wednesday, June 29, 2011 9:30AM - 9:45AM |
L4.00002: Jetting Instabilities of Particles from Explosive Dispersal Robert Ripley, Laura Donahue, Fan Zhang The formation of post-detonation `particle' jets, which are characterized by ballistic conical structures followed by billowing wakes, is widely observed in particle dispersal from explosives. This paper analyzes experimental observations to examine the mechanism for formation and growth of such particle jetting instabilities, and to propose a model to address the issues of jetting growth at a macroscopic level. Cylindrical charges employed a range of central explosive masses for dispersal of dry solid powder, pure liquid, or a hybrid mixture of solid powder and liquid. The results demonstrate that the jets form very early, and that the number of jets is dependent on shock pressure at the charge perimeter, within the range of particle sizes studied. The jetting instabilities may therefore be initiated by shock interaction with the dense solid particle interfaces near the charge surface, followed by transverse particle motion from the interaction of shocked and turbulent wake flow around the particles. From the experiments, a macroscopic model is proposed, in which an edge perturbation on a scale proportional to the number of jets is employed, and the subsequent transverse particle motion is controlled by an attraction function. The model is implemented in the Chinook hydrocode and is capable of modeling the initiation and growth of particle jetting structures in large-scale dispersal, and the results are validated against experiments. [Preview Abstract] |
Wednesday, June 29, 2011 9:45AM - 10:00AM |
L4.00003: The Role of Vorticity and Turbulence on the Instability of a Dense Solid Particle Flow Fue-Sang Lien, Tao Xu, Fan Zhang The dense solid particle flow regime lies between the dilute particle flow and packed granular bed limit and its flow topology is characterized by a large number of particle interactions. Such a flow regime is frequently observed in the initial expansion of detonation products from a heterogeneous explosive containing solid particles. Due to the stochastic nature of the interactions, instability of particle trajectories occurs including clustering, agglomeration and collision, which may lead to a nonuniform spatial distribution or macroscopic particle jet structures. Large eddy simulations at mesoscale are used to gain insight into the physical mechanisms for this instability of particle dynamics, in which the Immersed Boundary Method is applied to simulate a group of randomly distributed moving particles in a post-detonation flow. A criterion is established to represent the tendency of particle agglomeration, either based on divergence of particle velocity related to the difference between strain-rate and vorticity invariants or time derivative of particle volume fraction. The criterion is further evaluated based on our mesoscale solutions in order to show the role and importance of each physical mechanism involved. Preliminary mesoscale results for dispersal of densely-packed particles in a cylindrical charge and its possible connection to the formation of macroscopic particle jet structure will be discussed. [Preview Abstract] |
Wednesday, June 29, 2011 10:00AM - 10:15AM |
L4.00004: Development of instabilities in explosively dispersed particles Yann Gregoire, Oren Petel, David Frost Previous experimental studies have shown that when a layer of solid particles is explosively dispersed, the particles often develop a non-uniform spatial distribution. The instabilities within the particles and at the particle layer interface likely form on the timescale of the shock propagation through the particles. The mesoscale perturbations are manifested at later times in experiments by the formation of coherent clusters of particles or jet-like particle structures, which are aerodynamically stable. The particle instabilities that occur in explosively dispersed particles are investigated with a mesh-free computational method (Smoothed Particle Hydrodynamics). The simulations are compared with experimental results for the dispersal of a spherical packed bed of particles surrounding a central explosive charge. Of particular interest is the effect of the particle density and charge/particle mass ratio on the susceptibility of the particles to form jets. [Preview Abstract] |
Wednesday, June 29, 2011 10:15AM - 10:30AM |
L4.00005: Interaction of a planar shock with an isotropic field of sound waves Juan Gustavo Wouchuk Schmidt, Cesar Huete Ruiz de Lira, Alexander L. Velikovich We present here an anaytical model that describes the linear interaction of a planar shock front with a field of randomly oriented acoustic waves. The dynamics of the interaction with a single mode is studied in detail at first. The mode averaging is performed as usual, by integrating over the angle that the pre-shock mode wavenumber vector forms with the normal to the shock front. In this way, averages of the turbulent kinetic energy, vorticity, density and sonic flux are analytically obtained as functions of the fluid compressibility and the shock strength. Good agreement with previous numerical results has been obtained [K. Mahesh, S. Lee, S. K. Lele, and P. Moin, J. Fluid Mech. \textbf{300}, 383 (1995)]. Comparison to the shock interaction with vortical and entropic perturbations is also shown. [Preview Abstract] |
Wednesday, June 29, 2011 10:30AM - 10:45AM |
L4.00006: Instabilities and turbulence originating from relaxation phenomena behind shock waves Matei I. Radulescu, Nick Sirmas A strong shock is typically followed by a zone of energy relaxation. In gases, for example, this energy relaxation involves inelastic collisions among the molecules, during which the kinetic energy of the microscopic motion of the molecules is progressively transferred into the energy of the internal modes (vibration, ionization, etc...) as the medium equilibriates thermally. On the time scales of the relaxation process, the system acts as a dissipative medium, i.e. a system in which the energy available in the translational modes of motion of the molecules (which define pressure) is lost to the internal modes. In the present work, we study via molecular dynamic calculations the dynamics of shock waves driven through a dissipative molecular medium. The medium is modeled as a collection of hard disks undergoing inelastic collisions. We show that such a dissipative medium is unstable and forms distinctive high density and low pressure clustered non-uniformities by the Goldhirsch-Zanetti instability mechanism (Goldhirsch \& Zanetti, Clustering instability in dissipative gases, Phys. Rev. Letters, 70(11), 1993). The results obtained may shed light on the turbulence observed experimentally behind strong shock waves and anomalous reactivity centers (hot-spots)in reactive media. [Preview Abstract] |
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