Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A33: Flow Instability: Richtmyer-Meshkov |
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Chair: Riccardo Bonazza, University Wisconsin Room: 615 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A33.00001: Characterization of Rapid Solid-Particle Dispersal by a Blast Wave Bertrand Rollin, Rahul Koneru, Bradford Durant, Frederick Ouellet The impulsive dispersal of a bed of solid particles is often accompanied by the late time formation of coherent aerodynamic structures identified as particle jets. Despite numerous experimental and numerical studies to date, the intricate mechanisms leading to the formation and selection of these jets have not been conclusively characterized. In light of recently published experimental work, numerical simulations of the problem are performed using the quasi-two-dimensional geometric setting of a Hele-Shaw cell. Explicitly, a dense and uniform volumetric distribution of solid particles shaped in the form of a right circular hollow cylinder is sandwiched between two solid plates separated by a small distance. The initial impulse to the particles is then given by a relatively weak air blast wave. The highly resolved point-particle simulations focus on the interplay between particle inertia and the gas-solid particle limit of classic hydrodynamic instabilities such as the Rayleigh-Taylor and the Richtmyer-Meshkov instabilities, in explaining the formation of internal and external particle jets. The initial overpressure and particle properties are used as control parameters in the quantification of the characteristics of the late-time particle jets. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A33.00002: Attenuation of transmitted shock by a particle-seeded layer Peter Vorobieff, Gustaaf Jacobs, Tz-Ting Hung We conduct an experimental and numerical study of a nominally planar interaction of a normal shock with a layer of particles embedded in gas (air). Prior experimental studies reveal that even a particle layer with a modest volume fraction of particles (1-9\%) produces a reflected pressure wave at Mach numbers above 1.4. The present work focuses on two aspects of the flow. First, we examine the transmitted pressure wave, using both experimental measurements and computational modeling, and seek to identify the influence of the system used to form the particle layer in experiments and any effects peculiar to the layer thickness. Second, we present a simple model describing perturbation growth in the gravity-driven particle layer before the shock arrival. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A33.00003: Acceleration of a Vortex Ring-Deformed Stratified Interface by a Planar Shock Wave Alex Ames, Chris Weber Vortices are a well-known mechanism of transport across stratified interfaces. When repeatedly shocked, preexisting vorticity-driven deformation of the interface provides greater leverage for baroclinic torque under subsequent acceleration. The locally axisymmetric baroclinic vorticity deposition is a primary source in the turbulent energy cascade, leading to anisotropically-oriented eddies at the inertial scale, producing deleterious interfacial mixing. In particular, the assembly of a uniform fusion hotspot in inertial confinement fusion capsules is disrupted by the protrusion of a cold vortical bubble arising from the remains of the fill tube.\\ The morphology and evolution of compressible, variable-density vortices upon shock acceleration is explored computationally using the MIRANDA hydrodynamics code. A laboratory-scale configuration comprising a vortex ring discharged upwards into a stably-stratified layer from the open end of a small shock tube is compared for hydrodynamic similarity to a representative ICF fill tube perturbation. Vortex evolution, baroclinic production during and following shock interaction, behavior of secondary vortices, and mixing intensification are detailed across a range of vortex strengths and Atwood \& Mach numbers. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A33.00004: The effect of membraneless initial conditions on the growth of Richtmyer-Meshkov instability. Mohammad Mansoor, Sean Dalton, Adam Martinez, Tiffany Desjardins, John Charonko, Kathy Prestridge The Richtmyer-Meshkov Instability (RMI) is described by the baroclinic generation of vorticity at a density stratified interface when impulsively accelerated. Here, we experimentally investigate the late-time RMI growth of sinuous perturbations of an air/sulfur hexafluoride interface subjected to a Mach 1.2 planar shock wave within the vertical shock tube (VST) facility at Los Alamos National Laboratory. Interface perturbations are established using a novel membraneless technique where cross-flowing Air and SF6 separated by oscillating splitter plate enter the shock tube with an undulating structure. It is found that late-time perturbation growth behavior depends significantly on initial perturbation wavelength and peak-to-valley amplitude as prescribed by the frequency and sweeping angles of the ``oscillating plate''. The results are compared with past nonlinear models for various scaled initial amplitudes (ka$_{\mathrm{0}})$ and used to propose an empirical rational function that captures the asymptotic behavior of perturbation growth for both low and high scaled initial amplitudes. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A33.00005: Time-Resolved Particle Image Velocimetry of the 3-D, Multi-Mode Richtmyer-Meshkov Instability Jeffrey Jacobs, Everest Sewell, Kevin Ferguson We present recent experiments conducted on the multi-mode Richtmyer-Meshkov instability (RMI) using time-resolved Particle Image Velocimetry (PIV), comparing results initiated using high and low amplitude initial perturbations. Measurements of the growth parameter $\theta $ indicate a slight difference in growth rate exists between the two groups following the incident shock interaction, with additional differences in the growth of the instability following reshock. We validate a novel method of obtaining $\theta $ from the decay of turbulent kinetic energy (Thornber et al., J. Fluid Mech., 2010). Examination of the anisotropy ratio reveals an asymptotic value of approximately 1.8 in high amplitude experiments, with low amplitude experiments exhibiting decreasing anisotropy. High amplitude experiments exceed the threshold for mixing transition (Dimotakis, J. Fluid Mech., 2000) following the incident shock, with low amplitude experiments remaining below the threshold for most times. An extension of this analysis for developing flows (Zhou et al., Phys Rev E, 2003) reveals that neither flow satisfies the extended criterion for mixing transition. This observation is supported by the lack of an apparent inertial range in the power spectra of velocity. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A33.00006: Scalar Power spectrum and Structure Function analysis of the Richtmyer-Meshkov Instability Upon Re-Shock Christopher Noble, Joshua Herzog, Alex Ames, Jason Oakley, David Rothamer, Riccardo Bonazza The Richtmyer-Meshkov instability of a twice-shocked gas interface is investigated in the vertical shock tube of the Wisconsin Shock Tube Laboratory at the University of Wisconsin-- Madison. The initial condition is a shear layer, containing broadband perturbations, formed at the interface between a helium-acetone mixture and argon. The interface is accelerated with a shock of nominal strength M$=$1.9 with an initial Atwood number of A$=$0.43. Acetone is used as a molecular tracer for PLIF, allowing the extraction of concentration data by using a pulse burst laser system at 20kHz to excite acetone to fluoresce. The resulting fluorescence signal is measured using a high-speed Phantom camera. The evolution of the scalar power spectrum is investigated. As seen in previous single shock experiments a region of -5/3 slope is seen at late post-shock times, however at late re-shock times a larger region of -8/3 spectrum is observed. The measurement limit of the present experiments is estimated to be within the inertial range that may exist thus the measured slope is not expected to be a dissipation effect but the slope of the inertial range. Scalar structure functions are calculated, with the anomalous exponent being plotted against the structure function order also showing a non-KOC scaling. The terms in the scalar power spectrum evolution equation are calculated showing an asymmetry about the centre of the mixing layer and suggesting the emergence of an inertial range. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A33.00007: High-resolution, time-resolved PIV measurements on the Richtmyer-Meshkov instability in a dual-driver vertical shock tube. Kevin Ferguson, Everest Sewell, Jeffrey Jacobs Experiments on the Richtmyer-Meshkov Instability (RMI) using Particle Image Velocimetry (PIV) in a dual driver vertical shock tube are presented. Two shock waves generated at opposite ends of a vertical shock tube travel in opposing directions, impacting a perturbed interface formed between Air and Sulfur Hexaflouride ($\mathrm{SF}_6$). Perturbations are formed using a pair of voice coil driven pistons that generate Faraday waves on the interface. The incident shock wave arrives from the air side of the interface which initiates the RMI. Shortly afterward a second shock wave arrives from the $\mathrm{SF}_6$ side which generates reshock. Shock strengths are chosen to result in halted interface motion after passage of the second shock wave, permitting a long observational window in which the instability can evolve and yielding a simplified optical and recording setup as compared to typical single-driver experiments. Four cameras are utilized in a tiled pattern to create a high-speed recording of each experiment with a greatly increased final vector resolution compared to previous experiments. Information on the growth of the RMI, including measurements of the growth exponent, $\theta$, anisotropy, and turbulent kinetic energy decay are presented. [Preview Abstract] |
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