Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session R18: Flow Instability: Richtmyer-Meshkov II |
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Chair: Niranjan Ghaisas, Center for Turbulence Research, Stanford University Room: D135 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R18.00001: Richtmyer-Meshkov flow of elastic-plastic solids using a high-order Eulerian framework Niranjan S. Ghaisas, Akshay Subramaniam, Sanjiva K. Lele A high-order, fully Eulerian numerical framework is developed for tracking large, elastic-plastic deformations of solids coupled to fluids. Material interfaces are treated numerically using a diffuse-interface approximation. The numerical method is based on a 10$^{\mathrm{th}}$order compact finite difference scheme for spatial discretization, a 4$^{\mathrm{th}}$order Runge-Kutta time stepping method and a localized artificial diffusivity (LAD) method for regularizing shocks and material interfaces. This numerical framework was previously established for ideal gases and is extended in this study to liquids (stiffened gases) and solids. We establish the accuracy of our method by comparing to analytical results and demonstrate the superior resolution properties of our method by comparing to results of previous numerical studies that employed lower order methods. The effects of different equations of state and material stiffness parameters on the characteristics of the Richtmyer-Meshkov flow are investigated. [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R18.00002: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2016 1:56PM - 2:09PM |
R18.00003: Probabilistic events in shock driven multiphase hydrodynamic instabilities Wolfgang Black, Nick Denissen, Jacob McFarland Multiphase flows are an important and complex topic of research with a rich parameter space. Historically many simplifications and assumptions have been made to allow simulation techniques to be applied to these systems. Some common assumptions include no partilce-particle effects, evenly distributed particle fields, no phase change, or even constant particle radii. For some flows, these assumptions may be applicable but as the systems undergo complex accelerations and eventually become turbulent these multiphase parameters can create significant effects. Through the use of FLAG, a multiphysics hydrodynamics code developed at Los Alamos national laboratory, these assumptions can be relaxed or eliminated to increase fidelity and guide the development of experiments. This talk will build on our previous work utilizing simulations on the shock driven multiphase instability with a new investigation into a greater parameter space provided by additional multiphase effects; including a probabilistic particle field, various particle radii, and particle-particle effects on the evolution of commonly studied interfaces. [Preview Abstract] |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R18.00004: Growth-rate of Richtmyer-Meshkov instability for small and large amplitude initial perturbation Nora Swisher, Arun Pandian, Zachary Dell, Robert Stellingwerf, Snezhana Abarzhi We study the effect of the amplitude of the initial perturbation on Richtmyer-Meshkov instability (RMI) by means of Smooth Particle Hydrodynamics simulations and by the rigorous theory and the newly developed empirical model. A broad parameter regime is analyzed. Initially, the interface has a single-mode sinusoidal perturbation with the amplitude varying from 0\% to 100\% of its wavelength. An empirical model is developed to describe the non-monotone dependence of the RMI growth-rate on the initial amplitude. The initial growth rate of the interface has a peak value. The position of the peak depends only weakly on the Mach and Atwood numbers, whereas the peak value depends strongly on Atwood number and weakly on Mach number. The ratio of initial growth rate to background velocity is related to the energy partitioning between the interface and the bulk. We find an upper bound of the ratio of the interfacial energy to the bulk energy, and identified its scaling with the Atwood number. This peak value of the energy ratio indicates that RM interfacial growth can be controlled by initial conditions. [Preview Abstract] |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R18.00005: Dimensional crossover in Richtmyer-Meshkov flows Katsunobu Nishihara, Aklant K. Bhowmick, Snezhana Abarzhi We analyze nonlinear dynamics of large scale coherent structures in Richtmyer-Meshkov flows. Group theory based analysis is applied with a detailed consideration of RM dynamics invariant with respect to p2mm (3D rectangular), p4mm (3D square) and pm1 (2D) groups. Symmetry dictates that asymptotic solutions form a 2 parameter family for rectangular flows and a 1 parameter family for 3D square and 2D flows. For 3D square and 2D symmetry, asymptotic solutions are obtained for the 1st and 2nd order of approximation and the fastest growth rate occurs at zero bubble curvatures. Fourier amplitudes exponentially decay with increase in order showing that solutions are convergent. Both 2D and 3D square solutions are stable with respect to symmetry conserving perturbations. Isotropic 3D square solutions are universally stable, while 2D solutions are unstable to anisotropic perturbations. Furthermore, the 3D and 2D solutions cannot be continuously transformed from one to another, and the dimensional crossover is discontinuous. [Preview Abstract] |
Tuesday, November 22, 2016 2:35PM - 2:48PM |
R18.00006: Wave interference in Richtmyer-Meshkov flows Robert F. Stellingwerf, Arun Pandian, Snezhana Abarzhi While it is a conventional wisdom that the initial conditions determine the linear and nonlinear dynamics of the Richtmyer-Meshkov (RM) flows, the research in this area is focused primarily on the effects of the wavelength and amplitude of the interface perturbation. The information is hitherto largely ignored about the influences on the evolution of Richtmyer-Meshkov instability (RMI) of the relative phase of a multi-wave perturbation and the interference of the perturbation waves. In this work we report a detailed study of confluence of effects of the relative phase as well as amplitudes of the interfacial waves on the structure of bubbles and spikes that is formed at the RM unstable interface after the shock passage. We show that the phase and the wave interference are important factors of the dynamics, because they influence the RM flow qualitatively and quantitatively, including the symmetry of the interface, the morphology of spikes and bubbles, and the RMI growth. [Preview Abstract] |
Tuesday, November 22, 2016 2:48PM - 3:01PM |
R18.00007: Shock Driven Multiphase Instabilities in Scramjet Applications Jacob McFarland Shock driven multiphase instabilities (SDMI) arise in many applications from dust production in supernovae to ejecta distribution in explosions. At the limit of small, fast reacting particles the instability evolves similar to the Richtmyer-Meshkov (RM) instability. However, as additional particle effects such as lag, phase change, and collisions become significant the required parameter space becomes much larger and the instability deviates significantly from the RM instability. In scramjet engines the SDMI arises during a cold start where liquid fuel droplets are injected and processed by shock and expansion waves. In this case the particle evaporation and mixing is important to starting and sustaining combustion, but the particles are large and slow to react, creating significant multiphase effects. This talk will examine multiphase mixing in scramjet relevant conditions in 3D multiphase hydrodynamic simulations using the FLASH code from the University of Chicago FLASH center. [Preview Abstract] |
Tuesday, November 22, 2016 3:01PM - 3:14PM |
R18.00008: Two-fluid plasma Richtmyer-Meshkov instability Vincent Wheatley, Daryl Bond, Dale Pullin, Ravi Samtaney The Richtmyer-Meshkov instability of a shock accelerated perturbed density interface is computationally investigated in the context of ideal two-fluid plasmas. This is accomplished by numerically solving separate sets of conservation equations for the ions and electrons, coupled to the full Maxwell's equations. We focus on cases without an imposed magnetic field and with Debye lengths ranging from a thousandth to a tenth of the interface perturbation wavelength. For all cases investigated, the behavior of the flow is substantially different from that predicted by the Euler or ideal magnetohydrodynamics equations. Electric fields generated by charge separation cause interface oscillations, particularly in the electrons, that drive a secondary high-wavenumber instability. Consequently, the density interface is substantially more unstable than predicted by the Euler equations for all cases investigated. Self-generated magnetic fields are predicted within our simulations, but their orientation is such that they do not dampen the Richtmyer-Meshkov instability. [Preview Abstract] |
Tuesday, November 22, 2016 3:14PM - 3:27PM |
R18.00009: Effect of a seed magnetic field on two-fluid plasma Richtmyer-Meshkov instability Daryl Bond, Vincent Wheatley, Ravi Samtaney, Dale Pullin We investigate the effect of a uniform seed magnetic field on the plasma Richtmyer-Meshkov instability (RMI) using two-fluid simulations. These couple sets of conservation equations for the ions and electrons to the full Maxwell's equations. We consider cases where the seed magnetic field is normal to the interface and where the reference Debye length and Larmor radius range from a tenth to a thousandth of the interface perturbation wavelength. In ideal magnetohydrodynamics (MHD), it has been shown that in the presence of such a seed magnetic field, the growth of the RMI is suppressed by the transport of vorticity from the interface by MHD shocks. Our two-fluid plasma simulations reveal that while the RMI is suppressed in the presence of the seed field, the suppression mechanism varies depending on the plasma length-scales. Two-fluid plasma RMI simulations also reveal a secondary, high-wavenumber, electron-driven interface instability. This is not suppressed by the presence of the seed field. [Preview Abstract] |
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