Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session A19: Mini-Symposium: High-Speed, High-Energy Multimaterial Flows |
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Chair: Gustaaf Jacobs, San Diego State University Room: 28E |
Sunday, November 18, 2012 8:00AM - 8:26AM |
A19.00001: Development of a multiscale Eulerian-Lagrangian method for high-speed multi-material flows Uday Kumar Explosions and combustion processes generate environments where fluid turbulence and shocks have an intimate and mutual interaction with solid materials. While there has been considerable effort to determine suitable models for low speed (i.e. incompressible and low subsonic) flows and in solid mechanics, there is sparse work of this nature in the context of compressible (particularly shocked) multi-material flows. We seek to automate the development of particle transport models and closure by employing a multi-scale approach. In order to develop multi-scale modeling capabilities for high-speed particle-laden flows, we will discuss a joint effort that brings together a macro-scale, hig--order resolution Eulerian-Lagrangian method, and a micro-scale, full-resolution, high-fidelity first principle model for direct numerical simulations of shocked flows through heterogeneous media and micro-macro coupling. The multiscale approach is constructed in a hierarchical framework where high-fidelity DNS of particle interactions with shocked flows are employed at the micro-scale with full description of flow around resolved particles. At the macroscale the particles are modeled using Lagrangian point cloud methods. The linkage between scales is established through artificial neural networks (ANNs) trained to assimilate micro-scale physics and serve as closure models for the macro-scale simulations. [Preview Abstract] |
Sunday, November 18, 2012 8:26AM - 8:52AM |
A19.00002: Toward Rigorous Modeling of Extreme Compressible Multiphase Flows Y. Ling, M. Parmar, S. Annamalai, S. Balachandar, D.L. Frost Modeling is an important approach to investigate extreme compressible multiphase flows, such as explosive dispersal of particles/droplets and volcanic eruptions. Since the scale of practical interest is much larger than the particle size, point-particle models are usually employed in macro-scale simulations. We have developed a physics-based point-particle model, which divides the overall particle force and heat transfer into physically meaningful contributions. The effects of finite Reynolds and Mach numbers and finite particle volume fraction on each force and heat transfer contribution are incorporated. The model is used to simulate the problems of a planar shock wave interacting with a dense particle curtain and the rapid radial spreading of an annular bed of particles emplaced around a cylindrical explosive. In both cases the numerical results agree well with experimental data. Shock refractions that occur at the particle fronts generate reflected and transmitted shocks. These shocks introduce strong velocity and pressure gradients across the curtain, which causes the curtain to expand. The presentation will also discuss the modeling and simulation challenges of detonation-particle interaction and strong interparticle interaction arising from large volume fraction. [Preview Abstract] |
Sunday, November 18, 2012 8:52AM - 9:18AM |
A19.00003: Closure Models for Turbulent Particle-laden Flows from Particle-resolved Direct Numerical Simulation Shankar Subramaniam, Sudheer Tenneti, Mohammad Mehrabadi, Rahul Garg Gas-phase velocity fluctuations in fixed particle beds and freely evolving suspensions are quantified using a particle-resolved direct numerical simulation (PR-DNS). The flow regime corresponds to gas-solid systems typically encountered in fluidized bed risers, with high solid to gas density ratio and particle diameter being greater than the dissipative length scales. The kinetic energy associated with gas-phase velocity fluctuations in homogeneous monodisperse fixed beds is characterized as a function of solid volume fraction $\phi$ and the Reynolds number based on the mean slip velocity Re. A simple scaling analysis is used to explain the dependence of k on $\epsilon$ and Re. The steady value of k results from the balance between the source of k due to interphase transfer of kinetic energy, and the dissipation rate ($\epsilon$) of k in the gas-phase. It is found that the dissipation rate of k in gas-solid flows can be modeled using a length scale that is analogous to the Taylor microscale used in single-phase turbulence. Using the PR-DNS data for k and $\epsilon$ we also infer an eddy viscosity for gas-solid flow. For the parameter values considered here, the level of gas-phase velocity fluctuations in freely evolving suspensions differs by only 10\% from the value for the corresponding fixed beds. [Preview Abstract] |
Sunday, November 18, 2012 9:18AM - 9:44AM |
A19.00004: Modeling Detonation of Heterogeneous Explosives with Embedded Inert Particles Using Detonation Shock Dynamics: Normal and Divergent Propagation in Regular and Simplified Microstructure Scott Stewart We use a detonation shock propagation model, Detonation Shock Dynamics(DSD) to compute the interaction of a detonation shock wave that passes over a series of inert spherical particles embedded in a high explosive material. DSD provides an efficient means to study the dynamics of lead shock waves without the necessity of simulating the entire multi-material, reactive flow field. We derive partial differential equations for the motion of a detonation shock that obeys a linear shock normal velocity-curvature relation in a cylindrical coordinate system and in a moving, shock-attached coordinate system. The shock dynamics equations are solved numerically, in a unit-cell configuration. We describe the short-term and long-term behavior of the shock wave as it passes over the particles. We describe both the averages and character of the stochastic behavior that affects long-term average properties for microstructure in which the inert particles are periodically and randomly spaced. [Preview Abstract] |
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