Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session HP: Instability: Richtmyer-Meshkov |
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Chair: Riccardo Bonazza, University of Wisconsin-Madison Room: 200D |
Monday, November 23, 2009 10:30AM - 10:43AM |
HP.00001: PIV Analysis of the Richtmyer-Meshkov Instability for a He/SF$_{6}$ Interface Chris Weber, Nicholas Haehn, Jason Oakley, Mark Anderson, Riccardo Bonazza Experiments are presented for the Richtmyer-Meshkov instability of a nearly single mode interface of helium over sulfur hexafluoride. The initial condition is an interface created by oscillating a pair of rectangular pistons to form a nearly 2D sinusoidal standing wave in a vertical shock tube. The incident shock wave ($M$ = 1.2) deposits a large amount of vorticity on this high Atwood number ($A$ = ($\rho _{2}$--$\rho _{1})$/($\rho _{2}+\rho _{1})$ = 0.95) interface resulting in amplitude growth and asymmetrical spike/bubble development. Particle imaging velocimetry (PIV) is accomplished by seeding the top gas with Al$_{2}$O$_{3}$ particles and acquiring a pair of planar images that are analyzed to obtain the velocity field. Experimentally determined amplitude growth rate, circulation, and energy spectra are compared with models and numerical simulations. [Preview Abstract] |
Monday, November 23, 2009 10:43AM - 10:56AM |
HP.00002: Turbulence measurements in reshocked Richtmyer-Meshkov unstable curtains using stereo-PIV/PLIF B.J. Balakumar, Gregory Orlicz, Sridhar Balasubramanian, Peter Humphreys, Chris Tomkins, Kathy Prestridge Estimates of two important turbulence quantities, the density self-correlation parameter ($b$) and the generalized Reynolds stress tensor ($R_{12}$), have been experimentally obtained in Richtmyer-Meshkov unstable fluid layers after reshock using simultaneous PIV/PLIF diagnostics (Balakumar et. al., Phys. Fluids, 2008). We observe a double-peak structure in ``$b$'' at 4 times after reshock, with peaks coinciding with the edges of the turbulent structure. Whole-field histograms of the Reynolds stress follow symmetric distributions with equal contributions of positive and negative values, while spatial contour maps clearly show a streamwise asymmetry with large fluctuations preferentially occurring upstream of the centerline. We will also present preliminary stereo-PIV/PLIF measurements in the shock tube to explore the 3D behavior of the flow field before and after reshock. Statistical convergence estimates will be provided to illustrate the difficulties of obtaining true ensemble estimates in RM flows. [Preview Abstract] |
Monday, November 23, 2009 10:56AM - 11:09AM |
HP.00003: Mach number effects in shock-driven instabilities Greg Orlicz, B.J. Balakumar, Sridhar Balasubramanian, Chris Tomkins, Kathy Prestridge Experiments are performed to study the effects of incident shock Mach number on the development of a varicose-perturbed, heavy-gas curtain (air-SF6-air). Incident shock strength is varied from Mach 1.2 to 2.0, and the dynamic evolution of the gas curtain is observed using Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV). Previous work at the Los Alamos Gas Shock Tube (Orlicz et al. Phys. Fluids 2009), using the PLIF diagnostic to measure the temporal evolution of the density field, has shown that integral width growth rates for the curtain collapse using a scaling based upon the convection velocity of the curtain. However, the instantaneous mixing rate shows differences in mixing at scales smaller than the integral width, indicating that integral width alone is insufficient to describe the Mach effects on mixing. [Preview Abstract] |
Monday, November 23, 2009 11:09AM - 11:22AM |
HP.00004: Oblique shock acceleration of cylindrical gaseous interfaces and interaction with boundary layers Evan Johnson, Mario Chavez, Peter Vorobieff, C. Randall Truman We present experimental results obtained by shock acceleration of a gravity- and co-flow-stabilized cylindrical heavy gas (SF$_6$) jet embedded in lighter gas (air). The angle between the plane of the shock and the axis of the cylinder was varied between zero (planar interaction) and fifteen degrees (oblique interaction). The Mach number $M$ varied from 1.2 to 2.4, with most of the data acquired at $M=2$. We simultaneously acquired two views of the resulting flow -- top and side, using diffuse white light to visualize Mie scattering in submicron-sized droplets carried by the cylindrical jet. Our observations show that in the case of the planar shock-jet interaction, the boundary layers on the walls of the shock tube where the experiment was conducted do not appear to play a dramatic role. In the case of the oblique interaction, however, vorticity deposition produced by the shock interaction with the density gradients apparently leads to the jet material visibly interacting with one of the wall boundary layers. [Preview Abstract] |
Monday, November 23, 2009 11:22AM - 11:35AM |
HP.00005: Shock-resolved Navier-Stokes Simulation of the Richtmyer-Meshkov Instability Richard Kramer, Dale Pullin Results are presented from a numerical investigation of the Richtmyer-Meshkov instability, using a first-order perturbation of the two-dimensional Navier-Stokes equations about a one-dimensional unsteady shock-resolved base flow. This approach captures perturbations on the shocks and their influence on the interface growth to accurately examine the start-up and early linear growth phases of the instability. Weak, intermediate and strong incident shocks cases are examined for a single fluid and an Air/SF$_6$ mixture, across a range of contact-zone perturbation wave numbers, and compared to analytic models for transient and asymptotic growth of the instability. [Preview Abstract] |
Monday, November 23, 2009 11:35AM - 11:48AM |
HP.00006: On the Simulation of Shock-Driven Material Mixing in High Reynolds-Number Flows Fernando Grinstein, Akshay Gowardhan Implicit large eddy simulation proposes to effectively rely on the use of subgrid modeling and filtering provided implicitly by physics capturing numerics. Extensive work has demonstrated that predictive simulations of turbulent velocity fields are possible using a class of high resolution, non-oscillatory finite-volume (NFV) numerical algorithms. Truncation terms associated with NFV methods implicitly provide subgrid models capable of emulating the physical dynamics of the unresolved turbulent velocity fluctuations by themselves. The extension of the approach to the substantially more difficult problem of under-resolved material mixing by an under-resolved velocity field has not yet been investigated numerically, nor are there any theories as to when the methodology may be expected to be successful. Progress in addressing these issues in studies of shock-driven scalar mixing driven by Ritchmyer-Meshkov instabilities will be reported in the context of ongoing simulations of shock-tube laboratory experiments. [Preview Abstract] |
Monday, November 23, 2009 11:48AM - 12:01PM |
HP.00007: Simulation of Material Mixing in Shocked Gas-Curtain Experiments Akshay Gowardhan, Fernando Grinstein The unique combination of shock and turbulence emulation capabilities supports direct use of implicit large eddy simulation (ILES) as an effective simulation anzatz in shock-driven mixing research. This possibility is demonstrated in the context of a prototypical case study for which available laboratory data can be used to test and validate the ILES modeling. An SF6 gas curtain is formed by forcing SF6 through a linear arrangement of round nozzles into the shocktube test section. The gas curtain is shocked (M=1.26, M=1.5), and its later evolution subject to Ritchmyer-Meshkov flow instabilities, transition, and non-equilibrium turbulence phenomena are investigated based on high resolution simulations for shocked and reshocked cases. The particular strategy tested here is based on a nominally-inviscid simulation model using the LANL RAGE code and adaptive mesh refinement. Initial conditions for ILES are based on emulating the physics of SF6 falling through the test section of the shock tube until a steady state is reached using a separate 3D Navier-Stokes code which solves incompressible flow in the Boussinesq approximation. [Preview Abstract] |
Monday, November 23, 2009 12:01PM - 12:14PM |
HP.00008: Mixing asymmetry in variable density turbulence Daniel Livescu, Ray Ristorcelli, Robert Gore The homogenization of a heterogeneous mixture of two pure fluids with different densities by molecular diffusion and stirring induced by buoyancy generated motions is studied using Direct Numerical Simulations in two configurations: a) classical Rayleigh-Taylor instability using a $3072^3$ data set (Cabot and Cook, Nature Phys. 2006, Livescu et al, J. Turb. 2009) and b) an idealized triply periodic Rayleigh-Taylor flow named hereafter homogeneous Rayleigh-Taylor (HRT), using up to $1024^3$ meshes (Livescu and Ristorcelli, J. Fluid Mech. 2007, 2008). As a consequence of the differential accelerations experienced by the fluids, important differences between the mixing in a variable density flow, as compared to the Boussinesq approximation, are observed. In short, the pure heavy fluid mixes more slowly than the pure light fluid: in HRT, an initially symmetric double delta density PDF is rapidly skewed, as the light pure fluid vanishes, and only at long times and small density differences it relaxes to a symmetric, Gaussian-like PDF. The effect is shown to be related to the local structure of the flow and consequences for the high Atwood number Rayleigh-Taylor mixing are discussed. [Preview Abstract] |
Monday, November 23, 2009 12:14PM - 12:27PM |
HP.00009: Initial conditions effects in shock-driven instabilities Sridhar Balasubramanian, B.J. Balakumar, Greg Orlicz, Chris Tomkins, Kathy Prestridge Recent work at LANL (Dimonte et al, Phys Fluids 2004, Ramaprabhu et al, JFM 2005) has shown that buoyancy-driven turbulence can be affected at late-time by initial conditions, and memory of the initial conditions is not lost. We study the initial condition parameters that impact the mixing and transition to turbulence in shock-driven, Richtmyer-Meshkov unstable flows. A detailed study of the impact of wavelength and amplitude of initial condition perturbations in a heavy gas curtain (air-SF6-air) is undertaken. Carefully controlled, membrane-free initial conditions with At=0.67 and shock Mach number of 1.2 are used to examine the effect of varying the initial modes of the gas curtain. The temporal and spatial evolution of the flow is measured using simultaneous Particle Image Velocimetry (PIV) and Planar-Laser Induced Fluorescence (PLIF). This work is supported by the Los Alamos Laboratory Directed Research and Development Program. [Preview Abstract] |
Monday, November 23, 2009 12:27PM - 12:40PM |
HP.00010: Numerical Study of Multi-Component Mixing in Shock-Accelerated Flows Using Localized Artificial Diffusivity Method Santhosh Shankar, Soshi Kawai, Sanjiva Lele There has been a long-standing interest in developing numerical algorithms for compressible multi-component flows. The performance of the localized artificial diffusivity method of Kawai et al. (JCP 2009) on such problems is demonstrated by comparing the results for simple test cases with exact solutions and previous numerical calculations. The scheme is then used to simulate a 2D shock-bubble interaction by solving the full compressible Navier-Stokes equations to study the underlying mechanisms of mixing in this flow. The initial concentration of the dense gas bubble is modeled and the initial flow conditions are matched to the experiments of Tomkins et al. (JFM 2008) where a Mach 1.2 shock in air interacts with a cylindrical column in SF6. The grid converged results of the mixing rate and profile are quantitatively compared with the experiments for validation. In addition 3D simulations of Richtmyer-Meshkov instability based on the experiments of Vetter and Sturtevant (Shock Waves 1995) will be presented with particular focus on the turbulent missing in terms of the mixing width, the mixing rate and turbulent spectra. [Preview Abstract] |
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