Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session M38: Flow Instability: Richtmyer-Meshkov I |
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Chair: Kathy Prestridge, Los Alamos National Laboratory Room: Portland Ballroom 255 |
Tuesday, November 22, 2016 8:00AM - 8:13AM |
M38.00001: Oscillations of a standing shock in the Richtmyer-Meshkov instability (II) Karnig Mikaelian In a typical Richtmyer-Meshkov experiment a fast moving flat shock strikes a stationary perturbed interface between fluids A and B creating a transmitted and a reflected shock, both of which are perturbed. We propose shock tube experiments in which the reflected shock is stationary in the laboratory. Such a standing shock undergoes well known damped oscillations. We present the conditions required for producing such a standing shock wave which greatly facilitates the measurement of the oscillations and their rate of damping. [Preview Abstract] |
Tuesday, November 22, 2016 8:13AM - 8:26AM |
M38.00002: Dynamics of Richtmyer-Meshkov (RM) mixing with reshock Swathi Mula, Stuart Craig, Kathy Prestridge Variable density mixing plays a very important role in a number of applications, including inertial confinement fusion, supernovae, and supersonic combustion ramjet engines. To better understand the dynamics of variable density mixing, experiments are developed at the Vertical Shock Tube (VST) facility at Los Alamos National Laboratory. At this facility, an initially perturbed density interface (air-SF6, Atwood number $=$ 0.6) is impulsively accelerated by a low Mach shock wave (Mach \textless 3), which induces Richtmyer-Meshkov (RM) mixing of the two fluids. Initial perturbations on the air-SF6 interface are generated by an oscillating flapper that initially separates the two fluids. The time evolution of RM mixing is studied by way of simultaneous density and velocity measurements using Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) techniques. For two separate initial conditions, the measurements capture the air-SF6 interface, at multiple time locations, before and after the passage of shock and reshock at Mach $=$ 1.3. At each time location, multiple instantaneous shots are acquired. From these measurements, we study the evolution of RM instability along with the dependence of mixing flow features (post-shock and reshock) on the initial conditions. [Preview Abstract] |
Tuesday, November 22, 2016 8:26AM - 8:39AM |
M38.00003: Circulation in blast driven instabilities Marc Henry de Frahan, Eric Johnsen Mixing in many natural phenomena (e.g. supernova collapse) and engineering applications (e.g. inertial confinement fusion) is often initiated through hydrodynamic instabilities. Explosions in these systems give rise to blast waves which can interact with perturbations at interfaces between different fluids. Blast waves are formed by a shock followed by a rarefaction. This wave profile leads to complex time histories of interface acceleration. In addition to the instabilities induced by the acceleration field, the rarefaction from the blast wave decompresses the material at the interface, further increasing the perturbation growth. After the passage of the wave, circulation circulation generated by the blast wave through baroclinic vorticity continues to act upon the interface. In this talk, we provide scaling laws for the circulation and amplitude growth induced by the blast wave. Numerical simulations of the multifluid Euler equations solved using a high-order accurate Discontinuous Galerkin method are used to validate the theoretical results. [Preview Abstract] |
Tuesday, November 22, 2016 8:39AM - 8:52AM |
M38.00004: Mixing and Turbulence Statistics in an Inclined Interface Richtmyer-Meshkov Instability Akshay Subramaniam, Sanjiva Lele The interaction of a Mach 1.55 shockwave with a nominally inclined interface is considered. Unlike the classical Richtmyer-Meshkov problem, the interface evolution is non-linear from early time and large highly correlated vortical structures are observed even after reshock. The simulations target the experiment of McFarland et. al. (2014). Simulations are performed using the Miranda code (Cook et. al., 2005) that uses high-order spectral-like numerics (Lele, 1992). Results from multiple grid resolutions up to 4 billion grid points establish grid convergence. Comparisons to the experiments show that the simulations adequately capture the physics of the problem. Analysis of the data from the simulations based on variable density turbulence equations in the Favre averaged form will be presented. Statistics of unclosed terms in the variable density RANS equations will also be presented and compared to standard closure models. It is observed that the Reynolds Stresses have a non-monotonic return to isotropy after reshock and that compressibility effects are important long after reshock. The effect of numerics are also quantified and presented. [Preview Abstract] |
Tuesday, November 22, 2016 8:52AM - 9:05AM |
M38.00005: Emergence of power-law scalings in shock-driven mixing transition Peter Vorobieff, Patrick Wayne, Dell Olmstead, Dylan Simons, C. Randall Truman, Sanjay Kumar We present an experimental study of transition to turbulence due to shock-driven instability evolving on an initially cylindrical, diffuse density interface between air and a mixture of sulfur hexafluoride (SF$_6$) and acetone. The plane of the shock is at an initial angle $\theta$ with the axis of the heavy-gas cylinder. We present the cases of planar normal ($\theta = 0$) and oblique ($\theta = 20^\circ$) shock interaction with the initial conditions. Flow is visualized in two perpendicular planes with planar laser-induced fluorescence (PLIF) triggered in acetone with a pulsed ultraviolet laser. Statistics of the flow are characterized in terms of the second-order structure function of the PLIF intensity. As instabilities in the flow evolve, the structure functions begin to develop power-law scalings, at late times manifesting over a range of scales spanning more than two orders of magnitude. We discuss the effects of the initial conditions on the emergence of these scalings, comparing the fully three-dimensional case (oblique shock interaction) with the quasi-two-dimensional case (planar normal shock interaction). We also discuss the flow anisotropy apparent in statistical differences in data from the two visualization planes. [Preview Abstract] |
Tuesday, November 22, 2016 9:05AM - 9:18AM |
M38.00006: Time-resolved particle image velocimetry measurements of the 3D single-mode Richtmyer-Meshkov instability Qian Xu, Vitaliy V. Krivets, Everest G. Sewell, Jeffrey W. Jacobs A vertical shock tube is used to perform experiments on the single-mode three-dimensional Richtmyer-Meshkov Instability (RMI). The light gas (Air) and the heavy gas (SF$_{\mathrm{6}})$ enter from the top and the bottom of the shock tube driven section to form the interface. The initial perturbation is then generated by oscillating the gases vertically. Both gases are seeded with particles generated through vaporizing propylene glycol. An incident shock wave (M $\approx $ 1.2) impacts the interface to create an impulsive acceleration. The seeded particles are illuminated by a dual cavity 75W, Nd: YLF laser. Three high-speed CMOS cameras record time sequences of image pairs at a rate of 2 kHz. The initial perturbation used is that of a single, square-mode perturbation with either a single spike or a single bubble positioned at the center of the shock tube. The full time dependent velocity field is obtained allowing the determination of the circulation versus time. In addition, the evolution of time dependent amplitude is also determined. The results are compared with PIV measurements from previous two-dimensional single mode experiments along with PLIF measurements from previous three-dimensional single mode experiments. [Preview Abstract] |
Tuesday, November 22, 2016 9:18AM - 9:31AM |
M38.00007: Simulations of the Richtmyer-Meshkov Instability with experimentally measured volumetric initial conditions Kevin Ferguson, Everest Sewell, Vitaliy Krivets, Jeffrey Greenough, Jeffrey Jacobs Initial conditions for the Richtmyer-Meshkov instability (RMI) are measured in three dimensions in the University of Arizona Vertical Shock Tube using a moving magnet galvanometer system. The resulting volumetric data is used as initial conditions for the simulation of the RMI using ARES at Lawrence-Livermore National Laboratory (LLNL). The heavy gas is sulfur hexafluoride (SF6), and the light gas is air. The perturbations are generated by harmonically oscillating the gasses vertically using two loudspeakers mounted to the shock tube which cause Faraday resonance, producing a random short wavelength perturbation on the interface. Planar Mie scattering is used to illuminate the flow field through the addition of propylene glycol particles seeded in the heavy gas. An \textit{M=1.2} shock impulsively accelerates the interface, initiating instability growth. Images of the initial condition and instability growth are captured at a rate of 6 kHz using high speed cameras. Comparisons between experimental and simulation results, mixing diagnostics, and mixing zone growth are presented. [Preview Abstract] |
Tuesday, November 22, 2016 9:31AM - 9:44AM |
M38.00008: Simulations and experiments of ejecta generation in twice-shocked metals Varad Karkhanis, Praveen Ramaprabhu, William Buttler, James Hammerberg, Frank Cherne, Malcolm Andrews Using continuum hydrodynamics embedded in the FLASH code, we model ejecta generation in recent target experiments [1], where a metallic surface was loaded by two successive shock waves. The experimental data were obtained from a two-shockwave, high-explosive tool at Los Alamos National Laboratory, capable of generating ejecta from a shocked tin surface in to a vacuum. In both simulations and experiment, linear growth is observed following the first shock event, while the second shock strikes a finite-amplitude interface leading to nonlinear growth. The timing of the second incident shock was varied systematically in our simulations to realize a finite-amplitude re-initialization of the RM instability driving the ejecta. We find the shape of the interface at the event of second shock is critical in determining the amount of ejecta, and thus must be used as an initial condition to evaluate subsequent ejected mass using a source model[2]. In particular, the agreement between simulations, experiments and the mass model is improved when shape effects associated with the interface at second shock are incorporated. [1] W. T. Buttler et al., J. Appl. Phys., 116 (2014). [2] F.J. Cherne et al., J. Appl. Phys., 118, 185901 (2015). [Preview Abstract] |
Tuesday, November 22, 2016 9:44AM - 9:57AM |
M38.00009: Experimental Investigation of the Richtmyer-Meshkov Instability Through Simultaneous Measurements of Concentration and Velocity Daniel Reese, Alex Ames, Chris Noble, Jason Oakley, Dave Rothamer, Riccardo Bonazza The present work investigates the evolution of the Richtmyer-Meshkov instability through simultaneous measurements of concentration and velocity. In the Wisconsin Shock Tube Laboratory at the University of Wisconsin, a broadband, shear-layer initial condition is created at the interface between helium and argon (Atwood number $A=$0.7). The helium is seeded with acetone vapor for use in planar laser-induced fluorescence (PLIF), while each gas in the shear layer cross flow is seeded with particulate TiO$_{\mathrm{2}}$, which is used to track the flow and allow for the Mie scattering of light. Once impulsively accelerated by a $M=$1.57 shock wave, the interface is imaged twice in close succession using a planar laser sheet containing both the second and fourth harmonic output (532 nm and 266 nm, respectively) of a dual-cavity Nd:YAG laser. Particle image pairs are captured on a dual-frame CCD camera, for use in particle image velocimetry (PIV), while PLIF images are corrected to show concentration. Velocity fields are obtained from particle images using the Insight 4G software package by TSI, and velocity field structure is investigated and compared against concentration images. Probability density functions (PDFs) and planar energy spectra (of both velocity fluctuations and concentration) are then calculated and results are discussed. [Preview Abstract] |
Tuesday, November 22, 2016 9:57AM - 10:10AM |
M38.00010: Experimental investigation of the effect of multimodal inclined interface on Richtmyer-Meshkov instability evolution Mohammad Mohaghar, John Carter, Benjamin Musci, Devesh Ranjan In~the Georgia Tech Shock Tube and Advanced Mixing Laboratory, the evolution of Richtmyer-Meshkov instability (RMI) which arises from two initial conditions, namely, a predominantly single mode, inclined interface between two gases, and a perturbed, multimodal, inclined interface are studied. The gas combination of nitrogen-acetone as light gas and carbon dioxide as heavy gas (Atwood number of 0.23) with an inclination angle of 80 degrees ($\eta $/$\lambda =$0.097) was chosen in this set of experiments. The interface is visualized using planar laser diagnostics (simultaneous PLIF/PIV measurements), once impulsively accelerated by a Mach\textasciitilde 1.55. The ensemble-averaged turbulence measurements of the density, velocity and density-velocity cross-statistics are used to investigate the effects of added secondary modes to the interface on the correlation between turbulence and mixing quantities. [Preview Abstract] |
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