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 A22: Instability: Rayleigh-Taylor I |
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Chair: Oleg Schilling, Lawrence Livermore National Laboratory Room: 2012 |
Sunday, November 23, 2014 8:00AM - 8:13AM |
A22.00001: The evolution of the Rayleigh-Taylor and Richtmyer-Meshkov instabilities in a finite height domain Snezhana I. Abarzhi We apply group theory analysis to systematically study the nonlinear evolution of the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities in a domain of a finite height. The fluids with similar and contrasting densities are considered in case of two-dimensional RT and RM instabilities that are driven by sustained and impulsive accelerations respectively. The flow is periodic normal to the acceleration direction and has no external sources. For the nonlinear boundary value problem a family of asymptotic solutions is found, and the properties of the family solutions as well as their stability are thoroughly analyzed. For the first time the relation is identified between the family parameter (e.g. the front curvature) and the velocity shear at the front. The growth-rate of shear-driven Kelvin-Helmholtz instability is evaluated. It is shown in the nonlinear RT and RM flows in finite height domain there is an intense motion in a vicinity of the front and there is effectively no motion away from the front. In a finite size the domain the flow is decelerating in comparison to the spatially extended case. The theory outcomes for the numerical modeling of the RT and RM instabilities and for the design of experiments are discussed. [Preview Abstract] |
Sunday, November 23, 2014 8:13AM - 8:26AM |
A22.00002: Exploring the effects of a rigid body on the evolution of the Rayleigh Taylor instability Christopher Brown, Stuart B. Dalziel This talk discusses the effects of a rigid solid boundary impeding the evolution of the Rayleigh-Taylor (RT) instability. Previous experimental studies e.g. those of Linden, Dalziel and Davies Wykes, amongst others, used a solid rigid barrier to separate the two layers which when removed revealed the RT unstable interface. But what happens if the barrier is only partially removed? Initially the interface grows classically, however, this is soon replaced by two circulation cells, one either side of the barrier. The circulation forces fluid from both layers onto the interface at $z=0$, resulting in a RT mixing zone superimposed onto the circulation cells. This RT mixing zone grows in a manner similar to that found by Andrews et al. for RT in water tunnels, except here the flow is modified by the end wall. Near to the end wall the two circulation cells are deflected vertically, stretching the mixing zone vertically along the end wall rapidly. Using a combination of ILES simulations and low Atwood number experiments this talk will present a model for a multi-stage mixing process, discussing the effects of the opening size on the density change of each layer, buoyancy driven flux through the opening and mixing efficiency.\\[4pt] \copyright British Crown Owned Copyright 2014/AWE. [Preview Abstract] |
Sunday, November 23, 2014 8:26AM - 8:39AM |
A22.00003: Exploring elastic and plastic regimes of Rayleigh-Taylor instability in solids Rinosh Polavarapu, Arindam Banerjee The elastic-plastic (EP) transition stage of Rayleigh-Taylor (RT) instability was studied in an accelerated elastic-plastic solid. A novel rotating wheel RT experiment with linear vibratory motion that centrifugally accelerates a test section with two-material interface was utilized. The test section 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 and wavelengths were analyzed earlier to find the effects of initial conditions on instability acceleration. Presently, the EP transition process for a stable interface before reaching the instability was verified by accelerating the test section to a magnitude which is slightly less than critical acceleration and imparting linear vibration which alters the radius of circular path and thus varies the magnitude of centrifugal force. The results were compared with various instability and EP transition criteria given by analytical growth models. [Preview Abstract] |
Sunday, November 23, 2014 8:39AM - 8:52AM |
A22.00004: Progress on Multicomponent Reynolds-Averaged Navier--Stokes Model Development and Validation for Rayleigh--Taylor and Reshocked Richtmyer--Meshkov Turbulent Mixing Oleg Schilling Recent progress on the development and validation of a new $K$--$\epsilon$ multicomponent Reynolds-averaged Navier--Stokes model is discussed. The model includes mixture molecular dissipation and diffusion terms, molecular and turbulent enthalpy diffusion terms, and models for pressure--dilatation and dilatation dissipation. The model has successfully been applied to a set of ten reshocked Richtmyer--Meshkov mixing experiments, and more recently to experiments with larger Mach numbers and various Atwood numbers. An extension of the model to include a modeled density variance transport equation is described. The three-equation model is applied to various Rayleigh--Taylor mixing cases with complex accelerations. The evolution of various turbulence statistics, fields, and turbulent transport equation budgets are compared among these cases to elucidate differences in the turbulence production, dissipation and diffusion mechanisms. It is also shown that the mechanical turbulence timescale is poorly correlated with the molecular mixing timescale determined by the time-evolution of the molecular mixing parameter. [Preview Abstract] |
Sunday, November 23, 2014 8:52AM - 9:05AM |
A22.00005: Dynamics of Rayleigh-Taylor driven flows at high Atwood numbers Mark Mikhaeil, Bhanesh Akula, Thomas Finn, Devesh Ranjan For the first time, detailed simultaneous density and velocity turbulent statistics for Rayleigh-Taylor instabilities at Atwood number of 0.75 are measured. A new density probe capable of measuring gas volumetric concentration directly is used in parallel to a three-wire probe to obtain instantaneous density and velocity components simultaneously. Particle Image Velocimetry (PIV) is also implemented to obtain field-wise measurements. The self-similarity behavior of the velocity statistics, corresponding probability density function (PDF) and spectra are presented. Mie-scattering images taken in both stream-wise and span-wise direction at different instability times have illustrated the turbulent structures visible in the instability. [Preview Abstract] |
Sunday, November 23, 2014 9:05AM - 9:18AM |
A22.00006: Rayleigh Taylor Instability with Acceleration Reversals Denis Aslangil, Andrew Lawrie, Arindam Banerjee Self-similar evolution to turbulence of Rayleigh Taylor Instability (RTI) is studied for various acceleration histories, using high resolution numerical simulations. Incompressible, three-dimensional flow is modelled by MOBILE, a massively parallel solver, here using the Implicit Large Eddy Simulation technique. In the current work, accel-deccel-accel profiles with different reversal times and different deceleration periods are applied to RTI problem, to analyze their effects on self-similar evolution of RTI. Simulations are initialized with two initial conditions having the same initial energy but differing in terms of their mode number range. We will discuss a number of metrics which include low order metrics like mix widths, growth constants, molecular mixing parameter, and higher order turbulence parameters like second and higher order moments, their dissipations, and production-dissipation ratios which will also be useful in validating mix models. [Preview Abstract] |
Sunday, November 23, 2014 9:18AM - 9:31AM |
A22.00007: Development of a Gas-Driven Implosion Device for the Study of Rayleigh-Taylor Instability in Gelatin Cylinders Andrew Higgins, Justin Huneault The study of Rayleigh-Taylor (RT) instability growth on the inner surface of imploding cylinders is relevant to a number of inertial confinement and magnetized target fusion schemes. More specifically, the feedthrough of perturbations on the outer surface of the cylinder to its inner surface can be a limiting factor in the convergence and compression provided by implosion schemes. A number of studies have been performed on gas-driven gelatin rings, providing an accessible manner to study the RT instability in a converging geometry. In this study, we present the development of a novel apparatus which uses the single point initiation of a detonable gas mixture that then wraps around a central plate to symmetrically implode gelatin cylinders. The implosion is visualized by high speed camera through a viewing window. The ability to independently vary the initial driving pressure and the internal cavity pressure, as well as the cylinder thickness, the initial perturbation size and mode number allows for the study of a wide range of feedthrough regimes. Of particular interest is the cylinder deceleration phase, where the gas in the cavity begins to decelerate the inner cylinder surface, leading to rapid growth of perturbations on the now RT unstable interface. [Preview Abstract] |
Sunday, November 23, 2014 9:31AM - 9:44AM |
A22.00008: On the two families of instability waves in rotating stratified media Christophe Millet, Jacques Vanneste, Francois Lott We reexamine the related problems of baroclinic instability of parallel shear flows, concentrating on the unbounded rotating stratified case. Two families of instability waves, each having a distinct 3D wave pattern and propagation characteristics, have been found. The key feature of one of the families of waves is the spatial transition, at the inertial critical level, from a balanced edge wave near the ground to gravity waves aloft. It is shown that at small Rossby numbers the classical WKB approach would fail to give even a first-order instability wave solution. A global solution based on the method of matched asymptotic expansions is constructed. Matching is carried out in a region where both the quasi-geostrophic and linear approximations hold. Matching the exponentially small terms that arise from the feedback of the inertia-gravity waves on the surface motion can be used to close the potential-temperature dynamics thereby providing a new model of surface dynamics. For large Rossby numbers, another family of instability waves has been found. This family of waves does not appear to have been clearly identified and systematically studied before. The physical mechanisms which give rise to this family of waves are discussed and reported here. [Preview Abstract] |
Sunday, November 23, 2014 9:44AM - 9:57AM |
A22.00009: The Zombie Instability: Using Numerical Simulation to Design a Laboratory Experiment Meng Wang, Suyang Pei, Chung-Hsiang Jiang, Pedram Hassanzadeh, Philip Marcus A new type of finite amplitude-instability has been found in numerical simulations of stratified, rotating, shear flows. The instability occurs via baroclinic critical layers that create linearly unstable vortex layers, which roll-up into vortices. Under the right conditions, those vortices can form a new generation of vortices, resulting in ``vortex self-replication'' that fills the fluid with vortices. Creating this instability in a laboratory would provide further evidence for the existence of the instability, which we first found in numerical simulations of protoplanetary disks. To design a laboratory experiment we need to know how the flow parameters --- shear, rotation and stratification, etc. affect the instability. To build an experiment economically, we also need to know how the finite-amplitude trigger of the instability scales with viscosity and the size of the domain. In this talk, we summarize our findings. We present a map, in terms of the experimentally controllable parameters, that shows where the instability occurs and whether the instability creates a few isolated transient vortices, a few long-lived vortices, or long-lived, self-replicating vortices that fill the entire flow. [Preview Abstract] |
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