scholarly journals Rayleigh-Taylor instability in variable density swirling flows

2012 ◽  
Vol 85 (2) ◽  
Author(s):  
B. Dipierro ◽  
M. Abid
Keyword(s):  
Variable Density ◽  
Swirling Flows ◽  
Taylor Instability ◽  
Rayleigh Taylor Instability

scholarly journals Corrigendum

1975 ◽  
Vol 14 (3) ◽  
pp. 551-552
Author(s):  
P. K. Bhatia
Keyword(s):  
Variable Density ◽  
Plasma Phys ◽  
Taylor Instability ◽  
Dynamical Stability ◽  
Neutral Gas ◽  
Rayleigh Taylor Instability

‘On effects of neutral gas friction and ion viscosity on the Rayleigh-Taylor instability of a stratified plasma in the presence of Hall currents’By P. K. Bhatia,J. Plasma Phys. vol. 11, 1974, pp. 1–10Bhatia (1974) investigated the effects of neutral gas friction and ion viscosity on the dynamical stability of a composite plasma of variable density in the presence of the effects of Hall currents.

scholarly journals On the “Early-Time” Evolution of Variables Relevant to Turbulence Models for the Rayleigh-Taylor Instability

2010 ◽  
Author(s):  
Bertrand Rollin ◽  
Malcolm J. Andrews
Keyword(s):  
Turbulence Model ◽  
Initial Conditions ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Early Time ◽  
Variable Density ◽  
Taylor Instability ◽  
Turbulent Regime ◽  
Rayleigh Taylor Instability

We present our progress toward setting initial conditions in variable density turbulence models. In particular, we concentrate our efforts on the BHR turbulence model [1] for turbulent Rayleigh-Taylor instability. Our approach is to predict profiles of relevant variables before fully turbulent regime and use them as initial conditions for the turbulence model. We use an idealized model of mixing between two interpenetrating fluids to define the initial profiles for the turbulence model variables. Velocities and volume fractions used in the idealized mixing model are obtained respectively from a set of ordinary differential equations modeling the growth of the Rayleigh-Taylor instability and from an idealization of the density profile in the mixing layer. A comparison between predicted profiles for the turbulence model variables and profiles of the variables obtained from low Atwood number three dimensional simulations show reasonable agreement.

An Appropriate Metric to Switch on a Turbulence Model for Rayleigh-Taylor Instability Driven Mixing

2011 ◽  
Author(s):  
Bertrand Rollin ◽  
Malcolm J. Andrews
Keyword(s):  
Turbulence Model ◽  
Inertial Confinement Fusion ◽  
Initial Conditions ◽  
Turbulence Models ◽  
Variable Density ◽  
Taylor Instability ◽  
Engineering Applications ◽  
Modal Model ◽  
Rayleigh Taylor Instability ◽  
Rt Instability

Rayleigh-Taylor (RT) instability occurs at a perturbed interface between fluids of different densities, when the lighter fluid is accelerated into the heavier fluid (∇p · ∇ρ < 0, where p is pressure, and ρ is density). In time, as the two fluids seek to reduce their combined potential energy, the mixing becomes turbulent. This fundamental instability is observed, and plays a key role, in numerous natural phenomena, e.g. supernovae explosions, and in engineering applications, e.g. Inertial Confinement Fusion (ICF). The importance of initial condition (ICs) effects on the growth and mixing of Rayleigh-Taylor instability open an opportunity for “design” of RT turbulence for engineering, and question our current predictive capability. Indeed, commonly used turbulence models used for engineering applications are tuned for fully developed turbulence, whereas RT instability is a dynamic process that evolves toward turbulence under the influence of ICs. Therefore, our efforts aim at defining a procedure for properly accounting for initial conditions in variable density (RT) turbulence models. Our strategy is to have a model for the “early” evolution of the RT instability that will produce the initial conditions for the turbulence model. We already dispose of a modal model to evolve the RT mixing layer starting from almost any initial conditions. The present work is a first look at determining an appropriate metric for switching from the modal model to a variable density turbulence model.

scholarly journals Variable density and viscosity, miscible displacements in horizontal Hele-Shaw cells. Part 2. Nonlinear simulations

2013 ◽  
Vol 721 ◽  
pp. 295-323 ◽  
Author(s):  
M. O. John ◽  
R. M. Oliveira ◽  
F. H. C. Heussler ◽  
E. Meiburg
Keyword(s):  
Oil Recovery ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Viscous Fingering ◽  
Variable Density ◽  
Taylor Instability ◽  
Constant Density ◽  
Streamwise Vorticity ◽  
Miscible Displacements ◽  
Rayleigh Taylor Instability

AbstractDirect numerical simulations of the variable density and viscosity Navier–Stokes equations are employed, in order to explore three-dimensional effects within miscible displacements in horizontal Hele-Shaw cells. These simulations identify a number of mechanisms concerning the interaction of viscous fingering with a spanwise Rayleigh–Taylor instability. The dominant wavelength of the Rayleigh–Taylor instability along the upper, gravitationally unstable side of the interface generally is shorter than that of the fingering instability. This results in the formation of plumes of the more viscous resident fluid not only in between neighbouring viscous fingers, but also along the centre of fingers, thereby destroying their shoulders and splitting them longitudinally. The streamwise vorticity dipoles forming as a result of the spanwise Rayleigh–Taylor instability place viscous resident fluid in between regions of less viscous, injected fluid, thereby resulting in the formation of gapwise vorticity via the traditional, gap-averaged viscous fingering mechanism. This leads to a strong spatial correlation of both vorticity components. For stronger density contrasts, the streamwise vorticity component increases, while the gapwise component is reduced, thus indicating a transition from viscously dominated to gravitationally dominated displacements. Gap-averaged, time-dependent concentration profiles show that variable density displacement fronts propagate more slowly than their constant density counterparts. This indicates that the gravitational mixing results in a more complete expulsion of the resident fluid from the Hele-Shaw cell. This observation may be of interest in the context of enhanced oil recovery or carbon sequestration applications.

Effects of neutral gas friction and ion viscosity on the Rayleigh-Taylor instability of a stratified plasma in the presence of Hall currents

1974 ◽  
Vol 11 (1) ◽  
pp. 1-10 ◽  
Author(s):  
P. K. Bhatia
Keyword(s):  
Magnetic Field ◽  
Field Vector ◽  
Variable Density ◽  
Taylor Instability ◽  
Horizontal Magnetic Field ◽  
Unstable Stratification ◽  
Neutral Gas ◽  
Rayleigh Taylor Instability ◽  
The Magnetic Field ◽  
Proper Solutions

The effects of neutral gas friction, on the Rayleigh–Taylor instability of an infinitely conducting plasma of variable density, with ion viscosity and Hall currents, are investigated. For an ambient horizontal magnetic field, it is shown that the solution is characterized by a variational principle. Making use of the existence of this, proper solutions are obtained for a semi-infinite plasma, in which the density is stratified exponentially along the vertical, confined between two planes. In the simultaneous presence of the effects of ion viscosity and Hall currents, it is found that the potentially unstable stratification is unstable for all wavenumber perturbations, irrespective of whether or not the effects of neutral gas friction are included. Further, it is found that the growth rate increases with both Hall currents and neutral gas friction, and decreases with ion viscosity. The influence of the Hall currents and the neutral gas friction, therefore, is destabilizing, while that of ion viscosity is stabilizing. In the absence of Hall currents, it is found that the viscous plasma is stable, even for a potentially unstable stratification, for perturbations confined to a cone about the magnetic field vector. The angle of the cone of stable propagation of an inviscid plasma,. however, decreases with both Hall currents and effects of neutral gas friction.

Simulation of the Tilted Rig Experiment

2012 ◽  
Author(s):  
Bertrand Rollin ◽  
Malcolm J. Andrews
Keyword(s):  
Initial Perturbation ◽  
Mixing Layer ◽  
Variable Density ◽  
Taylor Instability ◽  
Two Dimensional ◽  
Two Fluids ◽  
Eddy Simulation ◽  
Type Variable ◽  
Rayleigh Taylor Instability ◽  
Variable Density Turbulence

The tilted rig experiment is a derivative of the rocket rig experiment designed to study mixing of fluids by the Rayleigh-Taylor instability. In the latter experiment, a tank containing two fluids of different densities is accelerated downwards between two parallel guide rods by a rocket motor. Misalignment between density and pressure gradients trigger the instability leading turbulence and mixing of the fluids. In the tilted rig experiment, the rocket rig is inclined by few degrees off the vertical before firing, creating a slanted initial perturbation interface. The purpose of the tilted rig experiment was to help with calibration of mixing models, as it is a unique two-dimensional Rayleigh-Taylor instability flow. We reproduce conditions similar to this experiment using a Monotone Integrated Large Eddy Simulation (MILES) technique, and for the first time look at statistics of turbulence quantities that appears in “RANS-type” variable density turbulence model. Our statistics show that for the most part, the turbulence quantities in this two-dimensional Rayleigh-Taylor instability configuration behave in a similar fashion as in the planar Rayleigh-Taylor instability configuration when looking in a direction perpendicular to the mixing layer centerline.

scholarly journals Simulations of the Tilted Rig Experiment Using the xRAGE and FLAG Hydrocodes

2012 ◽  
Author(s):  
Bertrand Rollin ◽  
Nicholas A. Denissen ◽  
Jon M. Reisner ◽  
Malcolm J. Andrews
Keyword(s):  
Turbulence Models ◽  
Variable Density ◽  
Taylor Instability ◽  
Massively Parallel ◽  
Mixing Models ◽  
Two Dimensional ◽  
Arbitrary Lagrangian Eulerian ◽  
Two Fluids ◽  
Rayleigh Taylor Instability ◽  
Variable Density Turbulence

The tilted rig experiment is a derivative of the rocket rig experiment designed to study mixing of fluids by the Rayleigh–Taylor instability. In this experiment, a tank containing two fluids of different densities is accelerated downwards between two parallel guide rods by a rocket motor. The rocket rig is inclined by a few degrees off the vertical to force a two-dimensional Rayleigh–Taylor instability. Thus, the tilted rig experiment can help calibrate two-dimensional mixing models. Simulations of the tilted rig experiments using two of Los Alamos National Laboratory’s hydrocodes are reported. Both codes, xRAGE and FLAG, are multidimensional, multimaterial, massively parallel, hydrodynamics codes that solve the Euler equations. xRAGE operates in an Eulerian framework, while FLAG operates in an Arbitrary Lagrangian–Eulerian (ALE) framework, with a Lagrange step followed by mesh relaxation and remapping. Direct comparisons between simulations and experimental results are reported, as well as report the behavior of the variable-density turbulence models implemented in the codes.

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