Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session L13: Rayleigh-Taylor/Richtmyer-Meshkov Instability |
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Chair: Jeffrey Jacobs, University of Arizona Room: 27A |
Monday, November 19, 2012 3:35PM - 3:48PM |
L13.00001: Turbulent mixing driven by a spherical converging shock M. Lombardini, D.I. Pullin, D.I. Meiron, R.A. Gore We present recent results from large-eddy simulations of the mixing induced at a perturbed spherical density interface initially impacted by a spherically convergent shock wave of Mach number $\simeq1.2$ at impact, and then re-shocked in the expansive phase. Two configurations are compared: i) air inside and SF$_6$ (five times denser than air) outside, i.e. heavy--light configuration; ii) SF$_6$ inside and air outside, or light--heavy configuration. From data interpolated over spherical surfaces, we compute various power spectra as well as extensive surface-averaged statistics involved in the budget of turbulent kinetic energy and enstrophy density. [Preview Abstract] |
Monday, November 19, 2012 3:48PM - 4:01PM |
L13.00002: Experiments on the Rayleigh-Taylor instability of gas-gas interfaces accelerated by an expansion wave Robert Morgan, Oleg Likhachev, Jeffrey Jacobs Experiments are presented in which a diffuse interface between two gases is accelerated to generate the Rayleigh-Taylor instability. The initially flat interface is generated by the opposing flow of two gases at matched volumetric flow rates. The interface is accelerated by an expansion wave generated by the rupturing of a diaphragm separating the heavy gas from a vacuum tank evacuated to approximately 0.1atm. The expansion wave generates a very high, O(1e3g0), but non-constant acceleration on the interface causing the Rayleigh-Taylor instability to develop. Shadowgraphy is employed to visualize the instability using two sets of three 200 mm diameter f/6.0 parabolic mirrors and three CMOS cameras operating at 10kHz with exposure times of 1e-6s. Planar Mie scattering is also employed using a planar laser sheet generated at the top of the apparatus which illuminates smoke particles seeded in the heavy gas. The scattered light is then imaged using three CMOS cameras operating at 10kHz. Experiments are shown in which a random perturbation is introduced by vertically oscillating the fluid interface to produce Faraday waves. [Preview Abstract] |
Monday, November 19, 2012 4:01PM - 4:14PM |
L13.00003: Progress on experimental investigation of RT instability at high Atwood numbers Bhanesh Akula, Devesh Ranjan The new multi layer experimental facility at Texas A{\&}M University can be used to study the mixing between two or more gas streams (separated by partitions initially) with different densities and velocities. This is a convective type system similar to the gas channel facility that was used to study RT mixing. This new suction-type multi layer facility has a test section double the size of the gas channel which will enable measurements up to Reynolds number of 30000. For the present study, this facility is used to study the Rayleigh-Taylor mixing between Air and Air-Helium mixtures at Atwood numbers greater than 0.5. Different diagnostics including Simultaneous PIV-PLIF and backlight imaging are used to obtain field wise measurement of velocities and densities as well as mixing width and its growth rate. The parameters obtained from these measurements including molecular mixing parameter $\theta$, turbulent quantities such as mean fluctuation of streamwise and cross stream velocities are presented. [Preview Abstract] |
Monday, November 19, 2012 4:14PM - 4:27PM |
L13.00004: Miscible and immiscible, forced and unforced experiments on the Rayleigh-Taylor instability Michael Roberts, Matthew Mokler, Jeffrey Jacobs Experiments are presented in which an incompressible system of two liquids is accelerated to produce the Rayleigh-Taylor instability. In these experiments, the initially stable, stratified liquid combination is accelerated downward on a vertical rail system in one of two experimental apparatuses: an apparatus in which a system of weights and pulleys accelerates the liquid filled tank, or a new apparatus which uses linear induction motors to accelerate the tank to produce much greater acceleration levels. Both miscible and immiscible liquid combinations are used. In both apparatuses the resulting fluid flows are visualized with backlit imaging using LED backlights in conjunction with monochrome high-speed video cameras, both of which travel with the moving fluid filled containers. Initial perturbations are either unforced and allowed to progress from background noise or forced by vertically oscillating the liquid combination to produce parametric internal waves. The mixing layer growth rate $\alpha $ is determined for all cases and compared to numerical simulations and past experiments. [Preview Abstract] |
Monday, November 19, 2012 4:27PM - 4:40PM |
L13.00005: Effects of Initial Conditions on Rayleigh-Taylor Instability in Elastic-Plastic Materials Pamela Roach, Arindam Banerjee In contrast to Newtonian fluids, experimental study of Rayleigh Taylor instability (RTI) in accelerated solids is traditionally hindered by difficulty to measure material properties and exceedingly small time scales of the processes. When an elastic-plastic solid is accelerated due to a density gradient, the instability is dependent on the material's mechanical strength, initial conditions, and acceleration that drive the instability. RTI in solids is observed in supernovas, explosive welding, and inertial confinement fusion. A novel experimental technique is used to study the effects of initial conditions and variable accelerations on the growth and instability in an elastic-plastic solid. The experiment consists of a container filled with air and mayonnaise, a non-Newtonian emulsion, with an initial perturbation between the two materials. Single mode perturbations of various amplitudes are analyzed and effects of two-dimensional versus three-dimensional interfaces are discussed. Furthermore, the instability threshold and stable elastic and plastic regions are investigated by controlling the acceleration. The instability threshold and perturbation growth rate are compared to linear analysis of incompressible RTI. [Preview Abstract] |
Monday, November 19, 2012 4:40PM - 4:53PM |
L13.00006: Compressibility and Stratification Effects on Single-Mode Rayleigh-Taylor Instability Scott Reckinger, Daniel Livescu, Oleg Vasilyev Simulations of single-mode compressible Rayleigh-Taylor instability (RTI) are performed using the Adaptive Wavelet Collocation Method (AWCM). Due to the physics-based adaptivity and direct error control of the method, AWCM is ideal for resolving the wide range of scales present in RTI growth. AWCM is used in conjunction with non-reflecting boundary conditions developed for highly stratified systems. This combination allows for extremely long domains, which is necessary for observing the late time growth of compressible RTI. The background state consists of two diffusively mixed stratified fluids of differing molar masses. Of interest are the compressibility effects on the departure time from the linear growth, the onset of strong non-linear interactions, and the late-time behavior of the fluid structures. For initial conditions corresponding to thermal equilibrium, the background stratification suppresses the instability growth when the molar masses are similar. A reversal in this monotonic behavior is observed for large molar mass differences, when stratification acts to enhance the bubble growth. The effects of the background stratification on the late-time vorticity generation and the associated induced velocities are also investigated. [Preview Abstract] |
Monday, November 19, 2012 4:53PM - 5:06PM |
L13.00007: Nonlinear evolution of Richtmyer-Meshkov and Rayleigh-Taylor instabilities in a domain of a finite size A. Qamar, S.I. Abarzhi We developed theoretical analysis to systematically study the nonlinear evolution of Richtmyer-Meshkov and Rayleigh-Taylor instability in a domain of a finite size. Fluids have either similar or contrasting densities, and acceleration is either impulsive or sustained. The flow is three-dimensional and periodic in the plane normal to the direction of acceleration, and has no external sources. Group theory analysis is applied to accurately account for the mode coupling. Asymptotic nonlinear solutions are found to describe the interface dynamics. The effect of the size of the domain on the diagnostic parameters of the flow is identified. In particular, it is shown that in a finite size the domain the flow is decelerated in comparison to the spatially extended case. The outcomes of the theoretical analysis results for the numerical modeling of the Richtmyer-Meshkov and Rayleigh-Taylor instabilities and for the design of experiments on high energy density plasmas are discussed. [Preview Abstract] |
Monday, November 19, 2012 5:06PM - 5:19PM |
L13.00008: Progress with Incline-Interface Richtmyer-Meshkov Experiments Jacob McFarland, Chris McDonald, David Reilly, Jeffery Greenough, Devesh Ranjan We describe our progress with a new experiment to investigate Richtmyer-Meshkov instability performed in the newly built variable inclination shock tube at Texas A{\&}M University. In the case of an inclined interface, the amount of vorticity deposited on the initial interface, can be easily controlled by changing the inclination angle, without changing the Mach (pressure gradient) or Atwood number (density gradient). We can achieve this goal by changing the inclination angle of the shock tube. This provides an easy-to-control, clean and repeatable interface for studying the RMI problem. Results will be presented from our initial experiments for a Mach 1.6 shock wave interaction with nitrogen over carbon-dioxide interface for an inclination angle of 60 degrees. Quantitative results such as the interface mixing width growth rate, and vorticity deposition will be discussed in detail. Numerical simulations of the experiments are performed using the ARES code (LLNL) and the time evolution of the interface width, measured from the experiments, is compared to the corresponding numerical predictions. [Preview Abstract] |
Monday, November 19, 2012 5:19PM - 5:32PM |
L13.00009: ABSTRACT WITHDRAWN |
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