Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D39: Flow Instability: Richtmyer-Meshkov I |
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Chair: Oleg Schilling, Lawrence Livermore National Laboratory Room: Sheraton Back Bay C |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D39.00001: A Comparative Study of Two-, Three- and Four-Equation Multicomponent Reynolds-Averaged Navier-Stokes Model Predictions of Turbulent Mixing in Reshocked Richtmyer-Meshkov Instability Oleg Schilling A multicomponent implementation of two-, three- and four-equation Reynolds-averaged Navier-Stokes models using either the turbulent kinetic energy dissipation rate or lengthscale as the second mechanical turbulence quantity is applied to model a Mach 1.5 reshocked Richtmyer-Meshkov instability in the light-to-heavy and heavy-to-light cases. The model includes mixture molecular transport terms, enthalpy diffusion terms, pressure-dilatation and dilatation dissipation models, and a molecular diffusion flux with contributions from baro- and thermodiffusion. The four-equation models couple transport equations for the mass flux $a_{i}$ and the negative density-specific volume correlation $b$ to the $K$-$\epsilon$ or $K$-$L$ equations, while the three-equation models use an algebraic closure for $b$. The evolution of various turbulence statistics, fields, and turbulent transport equation budgets are compared among these models to identify any differences in the turbulence production, dissipation and diffusion physics represented by the closures used in these models. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D39.00002: Richtmyer-Meshkov mixing: experiments on the effect of initial conditions Stuart Craig, Ricardo Mejia-Alvarez, Brandon Wilson, Kathy Prestridge The development of the Richtmyer-Meshkov instability (RMI) is sensitive to a number of parameters, including incident Mach number and the initial perturbation to the interface. A set of experiments at Los Alamos National Laboratory are underway using the Vertical Shock Tube (VST) with the aim of exploring the relationships between these two parameters. These experiments have been carried out with a single initial condition at three Mach numbers and at a single Mach number with three different initial conditions. This talk will focus specifically on the results on the effects of the different initial conditions on the early-time development of the RMI mixing at an air-SF$_6$ interface. Simultaneous measurements of the velocity (PIV) and density (PLIF) fields are used to explore the relationships between three types of initial conditions and the resulting early-time mixing at a single Mach number. Phase averaging of the flow field is employed in order to reduce intermittency and improve the statistical convergence of a number of turbulence statistics such as Favre-averaged Reynolds stresses, mixing rate, and enstrophy. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D39.00003: Experimental study of Mach number effects on the evolution of Richtmyer-Meshkov instabilities Ricardo Mejia-Alvarez, Brandon Wilson, Alex Craig, Kathy Prestridge The evolution of Richtmyer-Meshkov instabilities from the initial linear growth stages, to the subsequent non-linear interactions and the eventual (sometimes elusive) transition to turbulence, is strongly dependent on a number of factors such as shock strength (Mach number), Atwood number, and the initial structure of the fluid interface. Mach number controls the effective value of the Atwood number after compression, and thus the distribution and total amount of kinetic energy deposited at shock interaction. The initial scale-content in the fluid interface defines how quickly and to what extent growing instabilities interact with each other, ultimately conditioning transition to turbulence. These effects are not entirely independent of each other, and the extent of their relative importance is not well understood. To shed light on this subject, we designed a parameter space consisting of three different Mach numbers (1.1, 1.3, and 1.45) and three different interface configurations of varying scale content. This parameter space is being explored experimentally by means of simultaneous PIV/PLIF measurements on a single air-$SF_6$ interface as it evolves after shock interaction. This talk will focus on the observation of Mach number effects for an early stage of evolution. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D39.00004: Comparison of the Effects of Mach Number on the Spatiotemporal Evolution of Turbulence and Mixing in Reshocked Richtmyer-Meshkov Instability Tiberius Moran-Lopez, Oleg Schilling The predictions of a multicomponent $K$–$\epsilon$ Reynolds-averaged Navier-Stokes model applied to reshocked Richtmyer-Meshkov instability experiments with progressively larger incident shock Mach numbers are compared in detail. The model includes molecular dissipation and diffusion, mean and turbulent enthalpy diffusion, and closure models for pressure-dilatation and dilatation dissipation. This model was previously shown to give mixing layer widths in very good agreement with experimental data for a wide range of cases, including the Vetter-Sturtevant, Poggi et al., Leinov et al., and Houas-Chemouni experiments with Mach numbers ranging from $1.20$ to $4.20$. The spatiotemporal evolution of various statistics, fields, and transport equation budgets are compared among the cases considered here to quantify the effects of increasing Mach number on the intensity of turbulence and mixing both before and after reshock. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D39.00005: Numerical Simulations of the turbulent Richtmyer-Meshkov instability in a spherically convergent geometry Ismael Djibrilla Boureima, Praveen Ramaprabhu We investigate the development of the turbulent Richtmyer-Meshkov instability in a spherically convergent geometry. The three-dimensional simulations were performed using the astrophysical FLASH code [1], with a resolution of 1024 x 512 x 512 in the radial, azimuthal and polar directions for the multimode case. We present results from two sets of simulations, namely a spherical RM driven by a self-similar Chisnell [2] shock and an implosion problem defined by [3]. In both configurations, the shock travels from an outer fluid layer to an inner fluid that is denser. The implosion problem produces significantly greater convergence than the standard RM problem, allowing for significant enhancement of the turbulent mixing zone due to Bell-Plesset effects. We report on several quantities of interest from both simulations. \\[4pt] [1] Fryxell, B. et al., Astrophys. J. Suppl., 131 (1), 273 (2000).\\[0pt] [2] Chisnell, R. F, Proc. R. Soc. London, Ser. A, 232 (1955).\\[0pt] [3] Youngs, D. L., and Williams R. J., Intl. J Num. Meth. Fluids, 56 (8), 1597 (2008). [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D39.00006: Numerical, Dimensional, and Computational considerations in Large Eddy Simulations of the Richtmyer-Meshkov Instability Britton Olson The shock induced mixing of two gases separated by a perturbed interface is investigated through Large Eddy Simulation using two different high-order numerical methods. Results from a recently published collaborative study are presented which show remarkable similarities between quantities and metrics representing mixing and turbulence. Small differences between the results, however, do elucidate the differences in the two numerical methods and their strengths and weaknesses. Results from two-dimensional calculations of the same problem are also shown to highlight differences from the three-dimensional case. Finally, the feasibility in a hybrid compressible/incompressible calculation is discussed, which shows considerable computational savings as compared to the fully compressible case. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D39.00007: Linear Stability Analysis of Magnetohydrodynamic Richtmyer-Meshkov Instability in Cyindrical Geometry Abeer Bakhsh, Ravi Samtaney Numerical simulations and analysis in Cartesian slab geometry for nonlinear ideal magnetohydrodynamics (MHD) indicate that the Richtmyer-Meshkov instability (RMI) is suppressed in the presence of a magnetic field. An analytical solution of incompressible 2-D MHD RMI of an impulsively accelerated interface was investigated by Wheatley et al. (Phys. Rev. Lett. 2005; J. Fluid Mech. 2005) who found that, for a finite magnetic field, although the initial growth rate of the interface is unaffected by the presence of magnetic field, the late-time amplitude of the interface asymptotes to a constant value. In the framework of incompressible MHD, we examine analytically the behavior of an impulsively accelerated interface separating conducting fluids of different densities in {\em cylindrical} geometry. We investigate the stability properties of such a system and study the influence of the magnetic field on the growth rate of the interface. In converging cylindrical geometry, the RMI is followed by a Rayleigh-Taylor (RT) phase. Our analysis does not account for the RT phase of the instability but is valid for the duration of the RMI phase. We compare results of the incompressible analysis with linear compressible MHD simulations. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D39.00008: Suppression of the spherically converging magnetohydrodynamic Richtmyer-Meshkov instablity in an octahedrally symmetric seed magnetic field Wouter Mostert, Vincent Wheatley, Dale Pullin, Ravi Samtaney We present results of ideal magnetohydrodynamics simulations investigating the Richtmyer-Meshkov instability in near-spherical implosions in the presence of an octahedrally symmetric seed magnetic field. The problem is motivated by the desire to maintain a symmetrical collapse of the primary shock wave, minimally distorted by the effect of the seed magnetic field, while retaining the seed-field-induced suppression of the Richtmyer-Meshkov instability. The field is generated by a set of six current loops arranged around the target as on the faces of a cube. The instability is generated on a perturbed spherical density interface that is accelerated from the outside by imploding magnetohydrodynamic shocks, which are in turn generated by a spherical Riemann problem. The perturbation on the density interface is formed with a single-dominant-mode spherical harmonics expansion. We investigate the evolution of the interface and the transport of baroclinic vorticity near the interface, and examine the extent of the distortion to the primary magnetohydrodynamic shock system induced by the seed field. [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D39.00009: Multiphase Instabilities in Explosive Dispersal of Particles Bertrand Rollin, Frederick Ouellet, Subramanian Annamalai, S. ``Bala'' Balachandar Explosive dispersal of particles is a complex multiphase phenomenon that can be observed in volcanic eruptions or in engineering applications such as multiphase explosives. As the layer of particles moves outward at high speed, it undergoes complex interactions with the blast-wave structure following the reaction of the energetic material. Particularly in this work, we are interested in the multiphase flow instabilities related to Richmyer-Meshkov (RM) and Rayleigh-Taylor (RM) instabilities (in the gas phase and particulate phase), which take place as the particle layer disperses. These types of instabilities are known to depend on initial conditions for a relatively long time of their evolution. Using a Eulerian-Lagrangian approach, we study the growth of these instabilities and their dependence on initial conditions related to the particulate phase -- namely, (i) particle size, (ii) initial distribution, and (iii) mass ratio (particles to explosive). Additional complexities associated with compaction of the layer of particles are avoided here by limiting the simulations to modest initial volume fraction of particles. A detailed analysis of the initial conditions and its effects on multiphase RM/RT-like instabilities in the context of an explosive dispersal of particles is presented. [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D39.00010: Numerical Simulation of Multi-Material Mixing in an Inclined Interface Richtmyer-Meshkov Instability Akshay Subramaniam, Sanjiva Lele The Richtmyer-Meshkov instability arises when a shock wave interacts with an interface separating two fluids. In this work, high fidelity simulations of shock induced multi-material mixing between $N_2$ and $CO_2$ in a shock tube are performed for a Mach 1.55 shock interacting with a planar material interface that is inclined with respect to the shock propagation direction. In the current configuration, unlike the classical perturbed flat interface case, the evolution of the interface is non-linear from early time onwards. Our previous simulations of this problem at multiple spatial resolutions have shown that very small 3D perturbations have a large effect on vortex breakdown mechanisms and hence fine scale turbulence. We propose a comparison of our simulations to the experiments performed at the Georgia Tech Shock Tube and Advanced Mixing Laboratory (STAML). Results before and after reshock of the interface will be shown. Results from simulations of a second case with a more complex initial interface will also be presented. Simulations shown are conducted with an extended version of the Miranda solver developed by Cook et. al (2007) which combines high-order compact finite differences with localized non-linear artificial properties for shock and interface capturing. [Preview Abstract] |
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