Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session L21: Richtmeyer-Meshkov: Computational ApproachesInstabilities Reacting
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Chair: Jonathan Regele, Los Alamos National Laboratory Room: 706 |
Monday, November 20, 2017 4:05PM - 4:18PM |
L21.00001: Numerical analysis of high explosive driven Richtmyer-Meshkov instability Jonathan D. Regele, Alan K. Harrison, Juan A. Saenz, Marianne M. Francois The Richtmyer-Meshkov Instability (RMI) is a canonical problem that describes baroclinic fluid instability introduced by a shock or blast wave impacting a perturbed interface of two different density fluids. Most numerical studies of RMI use shock waves with constant driving pressure behind the shock to induce the instability. However, outside of experiments, little numerical work has been done to highlight the impact of the expansion (Taylor) wave, located just behind a detonation front, on the interface. In this work, a high explosive is used to initiate a blast wave and understand the impact of the expansion wave on the interface. -- Approved for unlimited release: LA-UR-17-26775. [Preview Abstract] |
Monday, November 20, 2017 4:18PM - 4:31PM |
L21.00002: A Computational Study of Richtmyer-Meshkov Instability with Surface Tension. Marianne Francois, Jan Velechovsky, Zach Jibben, Thomas Masser We have added the capability to model surface tension in our adaptive mesh refinement compressible flow solver, xRage. Our surface tension capability employs the continuum surface force to model surface tension and the height function method to compute curvatures. We have verified our model implementation for the static and oscillating droplets test cases and the linear regime of the Rayleigh-Taylor instability. With this newly added capability, we have performed a numerical study of the effects of surface tension on single-mode and multi-mode Richtmyer-Meshkov instability. [Preview Abstract] |
Monday, November 20, 2017 4:31PM - 4:44PM |
L21.00003: On Hydrodynamic Instabilities in Cylindrical Geometry Erik Proano, Bertrand Rollin Recent research has suggested that hydrodynamic instabilities induced mixing is one of the last major hurdles toward achieving optimum conditions for ignition in confined fusion approaches for energy production. We leave aside the complexities of multiple interacting physics that lead to a fusion target ignition to be able to focus on understanding the development of these hydrodynamic instabilities, namely Richtmyer-Meshkov and Rayleigh-Taylor, in the context of a converging geometry. The problem is reformulated into the cleaner case of a cylindrical shock wave imploding onto a pocket of Sulfur Hexafluoride$_{\mathrm{\thinspace }}$immersed in air. This numerical experiment aims at characterizing qualitatively and quantitatively the relation between the instabilities initial conditions and their development until late time. Starting from carefully designed single- and multimode disturbances at the initial density interface, our simulations track the evolution of the mixing layer through successive occurrences of the Richtmyer-Meshkov and Rayleigh-Taylor instabilities. Evolution of the mixing zone width and growth rate are presented for selected initial conditions, along with a quantification of mixing. Also, the effect of the converging shock strength is discussed. [Preview Abstract] |
Monday, November 20, 2017 4:44PM - 4:57PM |
L21.00004: Simulations of the Richtmyer-Meshkov Instability in a two-shock vertical shock tube Kevin Ferguson, Britton Olson, Jeffrey Jacobs Simulations of the Richtmyer-Meshkov Instability (RMI) in a new two-shock vertical shock tube configuration are presented. The simulations are performed using the ARES code at Lawrence-Livermore National Laboratory (LLNL). Two M=1.2 shock waves travel in opposing directions and impact an initially stationary interface formed by sulfur hexaflouride ($\mathrm{SF}_6$) and air. The delay between the two shocks is controlled to achieve a prescribed temporal separation in shock wave arrival time. Initial interface perturbations and diffusion profiles are generated in keeping with previously gathered experimental data. The effect of varying the inter-shock delay and initial perturbation structure on instability growth and mixing parameters is examined. Information on the design, construction, and testing of a new two-shock vertical shock tube are also presented. [Preview Abstract] |
Monday, November 20, 2017 4:57PM - 5:10PM |
L21.00005: Reynolds-Averaged Navier-Stokes Modeling of Weak, Moderate, and Strong Shock-Induced Richtmyer-Meshkov Turbulent Mixing Tiberius Moran-Lopez, Oleg Schilling Turbulent mixing of ideal gases (air and SF$_{6}$) induced by reshocked Richtmyer--Meshkov instability with Atwood number $At = -0.67$ (initially heavy-to-light) and shock Mach numbers $Ma = 1.05$, $1.25$, $1.56$, $3.00$, and $5.00$ is simulated using a weighted essentially nonoscillatory implementation of a multicomponent, two-equation Reynolds-averaged Navier--Stokes model. This study continues the previous application of this model to the $Ma = 1.24$, $1.50$, and $1.98$ Vetter--Sturtevant, $Ma = 1.45$ Poggi et al., and $Ma = 1.20$ Leinov et al. air/SF$_{6}$ cases to much larger Mach numbers. The cases considered are inspired by a large-eddy simulation study of transition to turbulence in singly-shocked Richtmyer--Meshkov instability over a progression of small-to-large Mach numbers by Lombardini, Pullin and Meiron (2012). Mixing layer widths, as well as various spatial mean and turbulent field profiles and statistics, are compared among the different Mach number cases and discussed. Other quantities signifying the intensity of the turbulence, such as the turbulent Reynolds number, are also compared and discussed. Turbulent transport equation budgets are used to assess the relative importance of the mechanisms contributing to turbulent mixing as the Mach number increases. [Preview Abstract] |
Monday, November 20, 2017 5:10PM - 5:23PM |
L21.00006: Mixing-model Sensitivity to Initial Conditions in Hydrodynamic Predictions Josiah Bigelow, Humberto Silva, C Randall Truman, Peter Vorobieff Amagat and Dalton mixing-models were studied to compare their thermodynamic prediction of shock states. Numerical simulations with the Sandia National Laboratories shock hydrodynamic code CTH modeled University of New Mexico (UNM) shock tube laboratory experiments shocking a 1:1 molar mixture of helium (He) and sulfur hexafluoride (SF$_{\mathrm{6}})$. Five input parameters were varied for sensitivity analysis: driver section pressure, driver section density, test section pressure, test section density, and mixture ratio (mole fraction). We show via incremental Latin hypercube sampling (LHS) analysis that significant differences exist between Amagat and Dalton mixing-model predictions. The differences observed in predicted shock speeds, temperatures, and pressures grow more pronounced with higher shock speeds. [Preview Abstract] |
Monday, November 20, 2017 5:23PM - 5:36PM |
L21.00007: Shock-driven Turbulent Mixing in Spherically Confined Geometries. Ismael Boureima, Praveen Ramaprabhu We report results from detailed numerical simulations of turbulent mixing generated by shock passage through a material interface separating two gases in a spherical configuration. The problem definition is similar to the spherical implosion defined by [1]. In this configuration, a spherical shock converges on a perturbed interface between gases with differing properties. During the implosion, perturbations at the interface are subjected to growth due to the RM instability, the RT instability, as well as Bell-Plesset effects. We report on several quantities of interest to the turbulence modeling community, including the turbulent kinetic energy, the anisotropy tensor, density self-correlation, atomic mixing etc. The simulations were performed using the FLASH code [2], at a resolution of 3072 x 1024 x 1024 in the radial, azimuthal and polar directions. We also report preliminary results from a study in which the convergence ratio of the implosion is varied by modifying the adiabatic index of the inner material. [1] Youngs, D. L., and Williams R. J., Intl. J Num. Meth. Fluids, 56 (8), 1597 (2008). [2] Fryxell, B. et al., Astrophys. J. Suppl., 131 (1), 273 (2000). [Preview Abstract] |
Monday, November 20, 2017 5:36PM - 5:49PM |
L21.00008: Evaporation effects in a shock-driven multiphase instability with a spherical interface Manoj Paudel, Jeevan Dahal, Jacob McFarland This talk presents results from 3D numerical simulations of a shock driven instability of a gas-particle system with a spherical interface. Two cases, one with an evaporating particle cloud and another with a gas only approximation of this particle cloud, were run in the hydrodynamics code FLASH, developed at University of Chicago. It is shown that the gas only approximation, a classical Richtmyer Meshkov instability, cannot replicate effects from particles like, lag, clustering, and evaporation. Instead, both gas hydrodynamics and particle properties influence one another and are coupled. Results are presented to highlight the coupling of interface evolution and particle evaporation. Qualitative and quantitative differences in the RMI and SDMI are presented by studying the change in gas properties like density and vorticity within the interface. Similarly, the effect of gas hydrodynamics on particles distribution and evaporation is studied. Particle evaporation rates are compared with 1D models and show poor agreement. The variation in evaporation rates for similar sized particles and the role of gas hydrodynamics in these variation is explored. [Preview Abstract] |
Monday, November 20, 2017 5:49PM - 6:02PM |
L21.00009: Numerical Study of Richtmyer-Meshkov Instability with Re-Shock Man Long Wong, Daniel Livescu, Sanjiva Lele The interaction of a Mach 1.45 shock wave with a perturbed planar interface between two gases with an Atwood number 0.68 is studied through 2D and 3D shock-capturing adaptive mesh refinement (AMR) simulations with physical diffusive and viscous terms. The simulations have initial conditions similar to those in the actual experiment conducted by Poggi et al. [1998]. The development of the flow and evolution of mixing due to the interactions with the first shock and the re-shock are studied together with the sensitivity of various global parameters to the properties of the initial perturbation. Grid resolutions needed for fully resolved and 2D and 3D simulations are also evaluated. Simulations are conducted with an in-house AMR solver HAMeRS built on the SAMRAI library. The code utilizes the high-order localized dissipation weighted compact nonlinear scheme [Wong and Lele, 2017] for shock-capturing and different sensors including the wavelet sensor [Wong and Lele, 2016] to identify regions for grid refinement. [Preview Abstract] |
Monday, November 20, 2017 6:02PM - 6:15PM |
L21.00010: The Richtmyer-Meshkov Instability on a Circular Interface in Magnetohydrodynamics Wolfgang Black, W. Curtis Maxon, Nicholas Denissen, Jacob McFarland Hydrodynamic instabilities (HI) are ubiquitous in high energy density (HED) applications such as astrophysics, thermonuclear weapons, and inertial fusion. In these systems, fluid mixing is encouraged by the HI which can reduce the energy yield and eventually drive the system to equilibrium. The Richtmyer-Meshkov (RM) instability is one such HI and is created when a perturbed interface between a density gradient is impulsively accelerated. The physics can be complicated one step further by the inclusion of Magnetohydrodynamics (MHD), where HED systems experience the effects of magnetic and electric fields. These systems provide unique challenges and as such can be used to validate hydrodynamic codes capable of predicting HI. The work presented here will outline efforts to study the RMI in MHD for a circular interface utilizing the hydrocode FLAG, developed at Los Alamos National Laboratory. [Preview Abstract] |
Monday, November 20, 2017 6:15PM - 6:28PM |
L21.00011: Comparing the Richtmyer-Meshkov instability of thermal and ion-species interfaces in two-fluid plasmas Vincent Wheatley, Daryl Bond, Yuan Li, Ravi Samtaney, Dale Pullin The Richtmyer-Meshkov instability (RMI) of a shock accelerated perturbed density interface is important in both inertial confinement fusion and astrophysics, where the materials involved are typically in the plasma state. Initial density interfaces can be due to either temperature or ion-species discontinuities. If the Atwood number of the interfaces and specific heat ratios of the fluids are matched, these two cases behave similarly when modeled using the equations of either hydrodynamics or magnetohydrodynamics. In the two-fluid ion-electron plasma model, however, there is a significant difference between them: In the thermal interface case, there is a discontinuity in electron density that is also subject to the RMI, while for the ion-species interface case there is not. It will be shown via ideal two-fluid plasma simulations that this causes substantial differences in the dynamics of the flow between the two cases. [Preview Abstract] |
Monday, November 20, 2017 6:28PM - 6:41PM |
L21.00012: A detailed study of bubble and spike velocities in ejecta Varad Karkhanis, Praveen Ramaprabhu, Frank Cherne, James Hammerberg, Malcolm Andrews We use detailed continuum hydrodynamics and molecular dynamics simulations to characterize bubble and spike growth in shock-driven ejecta. Insights from the simulations are used to suggest a modified expression for the velocity associated with ejected spike structures, while a recently proposed model [1] explains the observed bubble velocities. For spikes, existing models [2] can overpredict observed spike velocities if they do not include the modification of the initial spike growth rates due to nonlinearities. Instead, we find that using the potential flow model of [2], corrected with a suitable nonlinear prefactor leads to predictions in close agreement with our simulation data. We propose a simple empirical expression for the nonlinear correction for spike velocities that is able to reproduce results from our simulations and published experimental and simulation data over a wide range of initial conditions and Mach numbers. We verify these ideas with simulations (continuum and MD) at different amplitudes, initial perturbation shapes, and shock strength. This work was supported by the Los Alamos National Laboratory. [1] K. O. Mikaelian, Phys Rev Lett 80, 508 (1998). [2] Q. Zhang, Phys Rev Lett 81, 3391 (1998). [Preview Abstract] |
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