Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session L21: Instability: Richtmyer-Meshkov II |
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Chair: Kathy Prestridge, Los Alamos National Laboratory Room: 2010 |
Monday, November 24, 2014 3:35PM - 3:48PM |
L21.00001: DSMC Studies of the Richtmyer-Meshkov Instability M.A. Gallis, T.P. Koehler, J.R. Torczynski A new exascale-capable Direct Simulation Monte Carlo (DSMC) code, SPARTA, developed to be highly efficient on massively parallel computers, has extended the applicability of DSMC to challenging, transient three-dimensional problems in the continuum regime. Because DSMC inherently accounts for compressibility, viscosity, and diffusivity, it has the potential to improve the understanding of the mechanisms responsible for hydrodynamic instabilities. Here, the Richtmyer-Meshkov instability at the interface between two gases was studied parametrically using SPARTA. Simulations performed on Sequoia, an IBM Blue Gene/Q supercomputer at Lawrence Livermore National Laboratory, are used to investigate various Atwood numbers (0.33-0.94) and Mach numbers (1.2-12.0) for two-dimensional and three-dimensional perturbations. Comparisons with theoretical predictions demonstrate that DSMC accurately predicts the early-time growth of the instability. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Monday, November 24, 2014 3:48PM - 4:01PM |
L21.00002: Effects of Initial Conditions on the Mixing Transition of Richtmyer-Meshkov Instabilities Ricardo Mejia-Alvarez, Brandon Wilson, Kathy Prestridge A Richtmyer-Meshkov instability (RMI) might experience a mixing transition given the necessary Reynolds number and evolution time (Zhou \textit{et al., Phys. Rev. E}, 2003). Some studies over broadband initial conditions suggest that the emergence of a classical Kolmogorov $\kappa^{-5/3}$ inertial range, in an RMI that has experienced a mixing transition, is independent on the initial conditions. Since observations of this kind have not been replicated for single- or multi-mode perturbed interfaces, it is still premature to consider that the emergence of a Kolmogorov inertial range in RMI after the mixing transition is universal. To shed light on this subject, we are conducting high-resolution simultaneous PIV/PLIF measurements on a multi-mode perturbed interface between air and SF$_6$. Since our data are also intended for code validation, we used statistically stationary initial conditions, measuring the velocity and density fields both instantaneously and in an averaged sense. Based on our experimental data, we estimate a number of relevant turbulence statistics for different stages of the evolution of the shocked interface. [Preview Abstract] |
Monday, November 24, 2014 4:01PM - 4:14PM |
L21.00003: Oscillations of a standing shock in the Richtmyer-Meshkov instability Karnig Mikaelian Using the Richtmyer-Meshkov instability we present a method to study the damped oscillations of a standing shock, with and without viscosity. [Preview Abstract] |
Monday, November 24, 2014 4:14PM - 4:27PM |
L21.00004: Large-Eddy and Unsteady RANS Simulations of a Shock-Accelerated Heavy Gas Cylinder Brandon Morgan, Jeffrey Greenough Two-dimensional numerical simulations of the so-called ``shock-jet'' test problem for Richtmyer-Meshkov instability (RMI) are conducted using both large-eddy simulation (LES) and unsteady Reynolds-averaged Navier-Stokes (URANS) approaches in an arbitrary Lagrangian/Eulerian (ALE) hydrodynamics code. Turbulence statistics are extracted from LES by running an ensemble of simulations with multi-mode perturbations to the initial conditions. Detailed grid convergence studies are conducted, and LES results are found to agree well with both experiment and high-order simulations conducted by Shankar, Kawai, and Lele (Phys. Fluids, 2011). URANS results using a $k$-$L$ approach are found to be highly sensitive to the initialization of $L$ and to the time at which $L$ becomes resolved on the computational mesh. It is observed that a gradient diffusion closure for turbulent species flux is a poor approximation at early time, and a new closure based on the mass-flux velocity is proposed for low-Reynolds-number mixing. [Preview Abstract] |
Monday, November 24, 2014 4:27PM - 4:40PM |
L21.00005: Numerical investigation of 3D effects on a 2D dominated flow Daniel Reese, Christopher Weber A nominally two-dimensional interface, unstable to the Rayleigh-Taylor or Richtmyer-Meshkov instability, will become three-dimensional at high Reynolds numbers due to the growth of background noise and 3D effects like vortex stretching. This three-dimensionality changes macroscopic features, such as the perturbation growth rate and mixing, as it enhances turbulent dissipation. In this study a 2D perturbation with small-scale, 3D fluctuations is modeled using the hydrodynamics code Miranda. A Mach 1.95 shockwave accelerates a helium/SF6 interface, similar to the experiments of Motl et al. [1], to explore the regime where a 2D dominated flow will experience 3D turbulent effects. We report on the structure and growth of the post-shocked interface, as well as mixing measurements and energy spectra. These metrics are compared against 2D simulations to probe the influence of three-dimensionality on the evolution of the RMI. \\[4pt] [1] Motl et al., ``Experimental Validation of a Richtmyer-Meshkov Scaling Law Over Large Density Ratio and Shock Strength Ranges'' Phys. Fluids (2009) [Preview Abstract] |
Monday, November 24, 2014 4:40PM - 4:53PM |
L21.00006: A Numerical Investigation of Richtmyer-Meshkov Induced Vorticity in the Multi-Phase Interstellar Medium Gandhari Wattal, Sebastian Heinz, Riccardo Bonazza, Jason Oakley The interstellar medium (ISM) is inherently a multi-phase fluid, with density contrast of many orders of magnitude. Interstellar turbulence is one of the critical, poorly understood phenomena that regulate processes ranging from star formation to the formation of galactic structure. Baroclinic vorticity generated by the propagation of shocks through the multi-phase ISM is one of the potential drivers of turbulence and an important process in the distribution of momentum and energy into the ISM. We present hydrodynamic and magneto-hydrodynamic models of shock-bubble interactions that investigate the efficiency of vorticity generation in the ISM. The simulations are designed to complement laboratory experiments performed at the Wisconsin Shock Tube, with the goal to (a) calibrate the numerical method, and (b) to extend the investigation to regimes relevant for astrophysics but so far not reproducible in the lab (large magnetization, high Mach numbers). [Preview Abstract] |
Monday, November 24, 2014 4:53PM - 5:06PM |
L21.00007: Mach number effects on velocity and density measurements in Richtmyer-Meshkov mixing Brandon Wilson, Ricardo Mejia-Alvarez, Kathy Prestridge, Liuyang Ding Richtmyer-Meshkov (RM) mixing is sensitive to many parameters: incident Mach number, Atwood number, and initial interface perturbations. The correlation between turbulence and mixing quantities~and these parameters is not well-understood. The Vertical Shock Tube (VST) at Los Alamos National Lab is designed to measure the spectrum of scales existing in RM mixing growth and transition to turbulence. We use density (PLIF) and velocity (PIV) diagnostics to understand the effects of Mach number on an air-SF6 interface with multimode perturbations. We quantify Ma effects on the evolution of RM growth at large scales. We then statistically characterize the effect of shock strength on small scale turbulence and mixing ($e.g.$ Favre-averaged Reynolds stresses, instantaneous dissipation rate, and vorticity) at specific times after first shock. First shock mixing appears to transition to turbulence, and we examine the conditions of this transition. We also use first measurements of tomographic PIV in the vertical shock tube to investigate RM mixing anisotropy. [Preview Abstract] |
Monday, November 24, 2014 5:06PM - 5:19PM |
L21.00008: Experiments and simulations of single shock Richtmeyer-Meshkov Instability with measured, volumetric initial conditions Everest Sewell, Kevin Ferguson, Jeffrey Greenough, Jeffrey Jacobs We describe new experiments of single shock Richtmeyer-Meshkov Instability (RMI) performed on the shock tube apparatus at the University of Arizona in which the initial conditions are volumetrically imaged prior to shock wave arrival. Initial perturbation plays a major role in the evolution of RMI, and previous experimental efforts only capture a narrow slice of the initial condition. The method presented uses a rastered laser sheet to capture additional images in the depth of the initial condition shortly before the experimental start time. These images are then used to reconstruct a volumetric approximation of the experimental perturbation, which is simulated using the hydrodynamics code ARES, developed at Lawrence Livermore National Laboratory (LLNL). Comparison is made between the time evolution of the interface width and the mixedness ratio measured from the experiments against the predictions from the numerical simulations. [Preview Abstract] |
Monday, November 24, 2014 5:19PM - 5:32PM |
L21.00009: Shock-acceleration of a pair of gas inhomogeneities Jose Alonso Navarro Nunez, Daniel Reese, Jason Oakley, David Rothamer, Riccardo Bonazza A shock wave moving through the interstellar medium distorts density inhomogeneities through the deposition of baroclinic vorticity. This process is modeled experimentally in a shock tube for a two-bubble interaction. A planar shock wave in nitrogen traverses two soap-film bubbles filled with argon. The two bubbles share an axis that is orthogonal to the shock wave and are separated from one another by a distance of approximately one bubble diameter. Atomization of the soap-film by the shock wave results in dispersal of droplets that are imaged using Mie scattering with a laser sheet through the bubble axis. Initial condition images of the bubbles in free-fall (no holder) are taken using a high-speed camera and then two post-shock images are obtained with two laser pulses and two cameras. The first post-shock image is of the early time compression stage when the sphere has become ellipsoidal, and the second image shows the emergence of vortex rings which have evolved due to vorticity depostion by the shock wave. Bubble morphology is characterized with length scale measurements. [Preview Abstract] |
Monday, November 24, 2014 5:32PM - 5:45PM |
L21.00010: Shock-Driven Variable-Density Turbulence: New Insights David Reilly, Jacob McFarland, Devesh Ranjan Results are presented from a newly-constructed inclined shock tube facility which was used to study the coupled Richtmyer-Meshkov instability and Kelvin-Helmholtz instability before and after reshock. This study focuses on the effect of multiple initial conditions, which include two Atwood numbers (0.23 and 0.67), two Mach numbers (1.55 and 2.01), and two inclination angles (60$^\circ$ and 80$^\circ$). Mie scattering images of the interface development were acquired to track mixing width. Particle image velocimetry measurements were ensemble averaged over ten instantaneous realizations, which were used to determine circulation deposition as well as turbulent stresses and the cross correlation ($\overline{u\prime v\prime}$) across the mixing width. Furthermore, energy spectra were obtained for three stages of development before and after reshock. The most developed case exhibited the beginning of an inertial subrange after reshock, which may indicate a turbulent state has been reached. High-resolution planar laser-induced fluorescence was employed to obtain full-field density statistics. The density field was quantified with the density p.d.f. across the mixing width. [Preview Abstract] |
Monday, November 24, 2014 5:45PM - 5:58PM |
L21.00011: Computational Study of the Richtmyer-Meshkov Instability with a Complex Initial Condition Jacob McFarland, David Reilly, Jeffrey Greenough, Devesh Ranjan Results are presented for a computational study of the Richtmyer-Meshkov instability with a complex initial condition. This study covers experiments which will be conducted at the newly-built inclined shock tube facility at the Georgia Institute of Technology. The complex initial condition employed consists of an underlying inclined interface perturbation with a broadband spectrum of modes superimposed. A three-dimensional staggered mesh arbitrary Lagrange Eulerian (ALE) hydrodynamics code developed at Lawerence Livermore National Laboratory called ARES was used to obtain both qualitative and quantitative results. Qualitative results are discussed using time series of density plots from which mixing width may be extracted. Quantitative results are also discussed using vorticity fields, circulation components, and energy spectra. The inclined interface case is compared to the complex interface case in order to study the effect of initial conditions on shocked, variable-density flows. [Preview Abstract] |
Monday, November 24, 2014 5:58PM - 6:11PM |
L21.00012: Multicomponent Reynolds-Averaged Navier--Stokes Simulations of Reshocked Richtmyer--Meshkov Instability and Turbulent Mixing: Mach Number and Atwood Number Effects Tiberius Moran-Lopez, Oleg Schilling Reshocked Richtmyer--Meshkov turbulent mixing for various gas pairs and large shock Mach numbers is simulated using a third-order weighted essentially nonoscillatory (WENO) implementation of a new $K$--$\epsilon$ multicomponent Reynolds-averaged Navier--Stokes model. Experiments previously performed at the University of Provence with gas pairs CO$_2$/He, CO$_2$/Ar, and CO$_2$/Kr (with $At = -0.73$, $-0.05$, and $0.3$, respectively) and incident shock Mach numbers $M\!a = 2.4$, $3.1$, $3.7$, $4.2$, and $4.5$ are considered. The evolution of the mixing layer widths is shown to be in good agreement with the experimental data. Budgets of the turbulent transport equations are used to elucidate the mechanisms contributing to turbulent mixing in large Mach number reshocked Richtmyer--Meshkov instability. These results are contrasted with those from previous modeling of smaller Mach number experiments to identify the physical effects which require accurate modeling, including mean and turbulent enthalpy diffusion, pressure--dilatation, and dilatation dissipation. [Preview Abstract] |
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