... produced jets to electromagnetically driven wires in a Z-pinch, and to test various methods suggested for mitigation of the Rayleigh-Taylor instability ...
DTIC Science & Technology
... The target starts accelerating only after the hydrostatic equilibrium in it has been established by a passage of all shock and rarefaction waves back ...
A mode-coupling model is developed to treat the multimode evolution of the ablative Richtmyer-Meshkov (RM) and Landau-Darrieus (LD) instability in the laser imprint of planar targets. Using this mode coupling model, the multimode power spectrum of the RM and LD instability is computed. For the RM ...
Energy Citations Database
We report analytical and numerical solutions describing the evolution of the coherent structure of bubbles and spikes in the Richtmyer Meshkov instability in supernovae. It is shown that the dynamics of the flow is essentially non-local, and the nonlinear Richtmyer Meshkov bubble flattens and ...
NASA Astrophysics Data System (ADS)
Richtmyer-Meshkov (RM) instability occurs when a planar interface separating two fluids of different
NASA Technical Reports Server (NTRS)
Perturbations that seed Rayleigh-Taylor (RT) instability in laser- driven targets form during the early-time period. This time includes a shock wave transit from the front to the rear surface of the target, and a rarefaction wave transit in the opposite d...
National Technical Information Service (NTIS)
on whether the perturbations are initially at the front surface of the target (laser imprint, front surface from the front to the rear surface of the target, and a rarefaction wave transit in the opposite imprint and beam imbalance, roughness of the outer and inner surfaces of the target� contribute to the RT
E-print Network
Thin (400-800�) high-Z overcoat on the laser side of the target can be effective in suppressing laser imprint [S. P. Obenschain et al. Phys. Plasmas 9, 2234 (2002)]. The present experiments investigate the effect of the coating on instability seeding by target imperfections. Evolution of a pre-imposed ripple is observed by face-on x-ray radiography using Bragg reflection ...
We review experiments and calculations of the compressible Richtmyer- Meshkov instability from a single-mode, nonlinear initial perturbation. These experiments were performed using the Nova laser. Measurements of the time-evolution of the mixing region we...
The validity of gradient-diffusion closures for modeling turbulent transport in multi-mode Rayleigh Taylor and reshocked Richtmyer Meshkov instability-induced mixing is investigated using data from three dimensional spectral/tenth-order compact difference...
A vertical shock tube is used to perform experiments on the single-mode three-dimensional Richtmyer-Meshkov instability. The interface is formed using apposed flows of air and SF6 (with an Atwood number of 0.66) and the three-dimensional single-mode perturbation is created by the periodic vertical motion of the gases within the shock tube. Planar laser ...
Detonation initiation resulting from the Richtmyer Meshkov instability is investigated numerically in the configuration of the shock/spark-induced-deflagration interaction in a combustive gas mixture. Two-dimensional multi-species Navier Stokes equations implemented with the detailed chemical reaction model are solved with the ...
The goal of the EZturb mix model in KULL is to predict the turbulent mixing process as it evolves from Rayleigh-Taylor, Richtmyer-Meshkov, or Kelvin-Helmholtz instabilities. In this report we focus on a simple example of the Rayleigh-Taylor instability (w...
A series of experiments have been conducted to investigate the dynamic over-pressure stabilization of the ablative Richtmyer-Meshkov (RM) instability in inertial confinement fusion (ICF) targets during the start-up phase of implosion. Theory and hydrodynamic simulations predict that due to localized thermal flux variations modulating ...
The geometry of the two-dimensional standard computational test problems is generalized to three dimensions. Results corresponding to one particular test problem are presented in both two and three dimensions for comparison.
invariance with respect to shock Mach number for fluid mixing statistics, such as growth rate and volume� cates into a transmitted shock and reflected wave. This stage is known as the shock refraction stage. At the end of the refraction stage, both the transmitted shock and reflected wave detach from the material
In the standard Richtmyer-Meshkov instability, perturbations at a shocked interface grow after the passage of a shock. Freeze-out refers to the phenomenon whereby the perturbations do not grow, i.e., freeze-out, after the passage of a shock. This is fairl...
Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, we present the first results from a computational study of such a system under d...
A numerical study of planar Richtmyer-Meshkov instability in fluids with Mie-Gr�neisen equations of state is presented and compared to similar perfect gas flows to expose the role of the equation of state. Results for single and triple-mode planar Richtmyer-Meshkov instability, when a reflected shock wave occurs, ...
Cylindrical experiments were performed on the OMEGA laser at the University of Rochester to study unstable interfaces in single and double shells. For single shells a marker layer of more opaque and higher density material is placed between foam and an outside ablator. The marker is either smooth or with a well defined surface roughness. For double shells an inner cylinder is ...
Fully nonlinear motion of a circular interface in incompressible Richtmyer-Meshkov instability is investigated by treating it as a nonuniform vortex sheet between two different fluids. There are many features in cylindrical geometry such as the existence of two independent spatial scales, radius and wavelength, and the ingoing and outgoing growth of ...
The classical Richtmyer-Meshkov (RM) instability develops when a planar shock wave interacts with a corrugated interface between two different fluids. A larger family of so-called RM-like hydrodynamic interfacial instabilities is discussed. All of these feature a perturbation growth at an interface, which is driven mainly by vorticity, ...
A theoretical framework to study linear and nonlinear Richtmyer-Meshkov instability (RMI) is presented. This instability typically develops when an incident shock crosses a corrugated material interface separating two fluids with different thermodynamic properties. Because the contact surface is rippled, the transmitted and reflected ...
PubMed
Dynamic overpressure sets the growth rate of the ablative Richtmyer--Meshkov (RM) instability and the seeds for subsequent growth of perturbations due to the Rayleigh--Taylor instability in directly driven ICF targets. It leads to temporal oscillations of the perturbed ablation front, which ...
Dynamic overpressure sets the growth rate of the ablative Richtmyer--Meshkov (RM) instability and the late-time imprint levels in directly driven ICF targets. It leads to temporal oscillations of the perturbed ablation front, which have been predicted analytically and observed experimentally,(Y. Aglitskiy et al.), ...
Heat-flow-induced dynamic overpressure at the perturbed ablation front of an inertial confinement fusion target can stabilize the ablative Richtmyer-Meshkov-like instability and mitigate the subsequent ablative Rayleigh-Taylor (RT) instability. A series of experiments was ...
The magnetically induced Richtmyer-Meshkov (RM) instability in a two-component Bose-Einstein condensate (BEC) is investigated. We construct and study analytical models describing the development of the instability at both the linear and nonlinear stages. The models indicate interesting features of the instability: ...
In inertial confinement fusion (ICF), the possibility of ignition or high energy gain is largely determined by our ability to control the Rayleigh-Taylor (RT) instability growth in the target. The exponentially amplified RT perturbation eigenmodes are formed from all sources of the target and radiation non-uniformity in a process called seeding. This process involves a variety ...
A varicose-profile, thin layer of heavy gas (SF6) in lighter gas (air) is impulsively accelerated by a planar, Mach 1.2 shock, producing Richtmyer-Meshkov instability. We present the first measurements of the circulation in the curtain during the vortex-dominated, nonlinear stage of the instability evolution. These measurements, based ...
Turbulent transport and mixing in the reshocked multi-mode Richtmyer-Meshkov instability is investigated using three-dimensional ninth-order weighted essentially non-oscillatory simulations. A two-mode initial perturbation with superposed random noise is used to model the Mach 1.5 air/SF{sub 6} Vetter-Sturtevant [1] experiment. The mass fraction ...
DOE Information Bridge
When a short (sub-ns) laser pulse deposits finite energy in a target, the shock wave launched into it is immediately followed by a rarefaction wave. If the irradiated surface is rippled, theory and simulations predict strong oscillations of the areal mass perturbation amplitude in the target [A. L. Velikovich et al., Phys. Plasmas 10, 3270 (2003).] The first experiment designed to observe this ...
Experiments have been designed to study feed-out/feed-in on the NOVA laser using planar targets mounted on a hohlraum with perturbations placed on the cold side. The code LASNEX was used to model the experiments. The first series of calculations was run for the following targets: 87 ?m Al, 80 ?m Al/10 ?m Be, 35 ?m Al, 32 ?m Al/10 ?m Be. A 4 ?m amplitude, 50 ?m wavelength perturbation was placed on ...
We derive a scaling relation for Richtmyer-Meshkov instability of incompressible fluids. The relation is tested using both numerical simulations and experimental data. We obtain collapse of growth rates for a wide range of initial conditions by using vorticity and velocity scales associated with the interfacial perturbations and the acceleration impulse. A curve fit to the ...
The Richtmyer-Meshkov instability after reshock is investigated in shock tube experiments at the Wisconsin Shock Tube Laboratory using planar laser imaging and a new high speed interface tracking technique. The interface is a 50-50% volume fraction mixtur...
for all surface perturbations during times typical for the jet breakup at zero magnetic #12;eld. 1 target including MHD e#11;ects and showed that magnetic #12;eld signi#12;cantly decreases surface instabilities cm long and 1 cm diameter ideal cylinder with no surface perturbations. The in uence of the proton
performed. Several theories have been developed by different approaches [1,12�15]. Most of previous with the experimental data. The theory shows that the decay of the growth rate of the instability which has been is 2/3kt. In this paper we construct a nonlinear theory for the growth rate of the unstable RM inter
We describe our progress with a new experiment to investigate Ma > 4 shock driven Richtmyer-Meshkov (RM) instability, with application to Inertial Confined Fusion (ICF). The experiment comprises a three inch diameter shock tube filled with Xe and He (Atwood=0.95), separated by a Aluminium mesh that supports microfilm. High explosive (HE) is used to ...
Experimental study of a shock-decelerated ablation front is reported. A planar solid plastic target is accelerated by a laser across a vacuum gap and collides with a lower-density plastic foam layer. While the target is accelerated, a fast Rayleigh-Taylor (RT) growth of the seeded single-mode perturbation at the ablation front is observed. After the ...
in spherical geometry for axisymmetric ow. We demonstrate scaling invariance with respect to shock Mach number, it bifur- cates into a transmitted shock and re ected wave. This stage is known as the shock refraction stage. At the end of the refraction stage, both the transmitted shock and re ected wave detach from
Here is a study about fluid flows (the hydrodynamic part of codes modeling the plasma dynamics) showing great gradients and unsteady flows (Rayleigh-Taylor, Richtmyer-Meshkov). The numerical resolution of these problems needs codes able to simulate the tr...
Progress is reported on work in the following areas: vortex dynamics and turbulence, fingers and bubbles in Hele-Shaw cells and unbounded fluid, vortex reconnection, pattern selection in solidifying systems, Richtmyer-Meshkov instability, Wavy-Taylor vortex flows, high reynolds number laminar flows, and lastly numerical analysis and dynamical systems. ...
The Richtmyer-Meshkov instability (RMI) at the ablation front of laser-irradiated planar targets is investigated by two-dimensional numerical hydrodynamics simulations. The linear evolution of perturbations seeded either by surface roughness or target inhomogeneity is studied for perturbation wavelengths in the range 10<=?<=400 ?m and laser intensity ...
The development of hydrodynamic instabilities at the interface between two fluids of different densities is one of the major limiting factors in the Inertial Confinement Fusion. To study this effect, the incompressible fluid model is widely used for describing the motion near the interface separating the two fluids (see Refs. 1, 2 and references therein). We obtain a new set ...
This volume of the LLE Review, covering the period October--December 1998, includes two articles addressing issues applicable to direct-drive ICF on the National Ignition Facility (NIF): laser-plasma interactions and laser-irradiation uniformity. Additional highlights of the research presented in this issue are: (1) P.B. Radha and S. Skupsky present a novel charged-particle diagnostic that ...
A cylinder of heavy gas (SF{sub 6}) in air is hit by a Mach 1.2 shock. The resultant Richtmyer-Meshkov instability is observed as it propagates through the test section of the shock tube. Six images are taken after shock impact, and the velocity field at one time is measured using Particle Image Velocimetry (PIV). The images of the density field show the ...
Richtmyer-Meshkov instability occurs when a shock wave impinges on an interface separating two fluids having different densities [1,2]. The instability causes perturbations on the interface to grow, bubbles and spikes, producing vortical structures which potentially result in a turbulent mixing layer. In addition to shock tube ...
Three-dimensional high-resolution simulations are performed of the Richtmyer- Meshkov (RM) instability for a Mach 6 shock, and of the passage of a second shock from the same side through a developed RM instability. The second shock is found to rapidly smear fine structure and strongly enhance mixing. Studies of the ...
The goal of the EZturb mix model in KULL is to predict the turbulent mixing process as it evolves from Rayleigh-Taylor, Richtmyer-Meshkov, or Kelvin-Helmholtz instabilities. In this report we focus on a simple example of the Rayleigh-Taylor instability (which occurs when a heavy fluid lies above a light fluid, and we perturb the ...
The interface between air and a rectangular block of sulphur hexafluoride (SF6), impulsively accelerated by the passage of a planar shock wave, undergoes Richtmyer�Meshkov instability and the flow becomes turbulent. The evolution of the interface was previously simulated using a multi-component model based on a thermodynamically consistent and fully ...
A vertical shock tube is used to perform experiments in which an interface is formed using opposed flows of air and SF6. A three-dimensional single-mode perturbation is created by the periodic vertical motion of the gases within the shock tube. Richtmyer-Meshkov instability is produced by an impulsive acceleration by a weak shock wave (Ms=1.2). Planar ...
The turbulent transport properties of multi-mode Richtmyer- Meshkov instability with reshock are investigated using data from a three-dimensional, ninth-order weighted essentially non- oscillatory (WENO) simulation of the Mach 1.5 air/SF6 Vetter- Sturtevant shock tube experiment. A spatial average over the periodic directions is used ...
To achieve thermonuclear ignition at Megajoule class laser systems such as the NIF using inertially confined plasmas, targets must be designed with high in-flight aspect ratios (IFAR) resulting in low shell stability. Recent simulations and experiments have shown that isolated features on the outer surface of an ignition capsule can profoundly impact capsule performance by leading to material ...
This work presents on-going research on large-eddy simulations of shock-generated mixing in Richtmyer-Meshkov flow in converging geometries. A hybrid numerical method is used on each subgrid of the mesh hierarchy within the AMROC (adaptive mesh refinement object oriented C++) framework: it is a shock capturing method but reverts to a centered scheme with low numerical viscosity in regions of ...
The dynamics of the reshocked multi-mode Richtmyer-Meshkov instability is investigated using 513 x 257{sup 2} three-dimensional ninth-order weighted essentially nonoscillatory shock-capturing simulations. A two-mode initial perturbation with superposed random noise is used to model the Mach 1.5 air/SF{sub 6} Vetter-Sturtevant shock tube experiment. The ...
Effects of high-Mach numbers and high initial amplitudes on the evolution of the single-mode Richtmyer-Meshkov shock-wave induced hydrodynamic instability are studied using theoretical models, experiments, and numerical simulations. Two regimes in which there is a significant deviation from the linear dependence of the initial velocity on the initial ...
The success of the inertial confinement fusion program is critically dependent on our ability to accelerate and implode the fuel capsules (targets) with a high degree of symmetry. Distortion of laser fusion targets, primarily by the Rayleigh-Taylor (RT) hydrodynamic instability, is a major obstacle to achieving ignition and high energy gain. Non-uniformities of the laser ...
The authors present results for high resolution hydrodynamic calculations of the growth and development of instabilities in shock driven imploding spherical geometries in both 2D and 3D. They solve the Eulerian equations of hydrodynamics with a high order Godunov approach using local adaptive mesh refinement to study the temporal and spatial development of the turbulent mixing ...
Richtmyer-Meshkov experiments are conducted on the Nova laser with strong radiatively driven shocks (Mach > 20) in planar, two-fluid targets with Atwood number A < 0. Single mode interfacial perturbations are used to test linear theory and 3D random perturbations are used to study turbulent mix. Rayleigh-Taylor experiments are conducted on a new facility called the ...
The reshocked single-mode Richtmyer-Meshkov instability is simulated in two spatial dimensions using the fifth- and ninth-order weighted essentially non-oscillatory shock-capturing method with uniform spatial resolution of 256 points per initial perturbation wavelength. The initial conditions and computational domain are modeled after the single-mode, Mach ...
The qualitative and quantitative relationship of numerical simulation to the physical phenomena being modeled is of paramount importance in computational physics. If the phenomena are dominated by irregular (i.e., nonsmooth or disordered) behavior, then pointwise comparisons cannot be made and statistical measures are required. The problem we consider is the gas curtain ...
The qualitative and quantitative relationship of numerical simulation to the physical phenomena being modeled is of paramount importance in computational physics. If the phenomena are dominated by irregular (i. e., nonsmooth or disordered) behavior, then pointwise comparisons cannot be made and statistical measures are required. The problem we consider is the gas curtain ...
Low Atwood number (A = (?2--?1)/(?2+?1) = 0.29) Richtmyer-Meshkov instability (RMI) experiments are presented for a near single mode, sinusoidal interface accelerated by an incident and a reflected shock wave. The interface is created by flowing a 50-50% mixture of He+Ar from above and pure Ar from below. Slots at the interface location allow for a ...
Several aspects of the sensitivity of a shock-ignited inertial fusion target to variation of parameters and errors or imperfections are studied by means of one-dimensional and two-dimensional numerical simulations. The study refers to a simple all-DT target, initially proposed for fast ignition (Atzeni et al 2007 Phys. Plasmas 7 052702) and subsequently shown to be also suitable for shock ignition ...
As a shock travels through the interface between substances of different densities, existing perturbations can grow via the Richtmyer-Meshkov (RM) instability. The study of the RM instability in a convergent geometry leads to a better understanding of implosions applicable to inertial confinement fusion and various astrophysical events, such as ...
The instability of shocked and reshocked perturbed interface between gases of different densities is analyzed by comparing flow visualization from 2D and 3D shock-tube experiments with 2D numerical simulations and theory. The shadowgraphs and calculations show similar large scales of mixing by fluid interpenetration induced by the Richtmyer-Meshkhov ...
We present an analytic theory of Richtmyer-Meshkov instabilities in an arbitrary number N of stratified fluids subjected to a shock. Following our earlier work on Rayleigh-Taylor instabilities, the theory assumes incompressible flow in which a shock is treated an impulsive acceleration, g = ..delta.. v delta(tau/sub s), ..delta..v being the jump velocity ...
Fluid instabilities like Rayleigh�Taylor (R�T), Richtmyer�Meshkov (R�M) and Kelvin�Helmholtz (K�H) instability can occur in a wide range of physical phenomenon from astrophysical context to Inertial Confinement Fusion (ICF). Using Layzer's potential flow model, we derive the analytical expressions of growth rate of bubble ...
The nonlinear evolution of the Richtmyer-Meshkov (RM) instability is investigated using numerical simulations with the FLASH code in two-dimensions (20). The purpose of the simulations is to develop a nonlinear model of the RM instability that is accurate to the regime of inertial confinement fusion (ICF) and ejecta formation, namely, at large Atwood ...
We present the results from a series of experiments recently completed on the Nova laser studying the growth of the Richtmyer-Meshkov instability from an initially nonlinear perturbation. These are the first experimental measurements of the time-dependent mixing of materials at a shocked interface from a high-amplitude, short-wavelength perturbation in a high Mach number ...
The authors conduct shock-tube experiments to investigate Richtmyer-Meshkov (RM) instability of a narrow curtain of heavy gas (SF{sub 6}) embedded in lighter gas (air). Initial perturbations of the curtain can be varied, producing different flow patterns in the subsequent evolution of the curtain. Multiple-exposure video flow visualization provides images ...
The goal of the EZturb mix model in KULL is to predict the turbulent mixing process as it evolves from Rayleigh-Taylor, Richtmyer-Meshkov, or Kelvin-Helmholtz instabilities. In this report we focus on a simple example of the Richtmyer-Meshkov instability (which occurs when a shock hits an interface between fluids of different ...
Works performed in the field of mathematical modeling of the process of mixing of gases of different densities on the interface between them under the action of transmitted and reflected shock waves and compression and rarefaction waves are reviewed. A mathematical model of two-velocity, two-temperature gases, which has been derived from the basic principles, is proposed for this modeling. A ...
Experiments have been conducted using the Nova laser system to investigate the growth of the Richtmyer-Meshkov (RM) instability resuling from a strong shock wave (M{approximately}30) crossing a prescribed well-defined initial multimode perturbation. The perturbation was a 100 mode superposition of 1 {micro}m amplitude sine waves with randomly generated phases between 0 and ...
The Richtmyer-Meshkov instability is a fundamental fluid instability that occurs when perturbations on an interface separating gases with different properties grow following the passage of a shock. This instability is typically studied in shock tube experiments, and constitutes a fundamental example of a complex hydrodynamic flow. ...
We present a numerical comparison study of planar Richtmyer-Meshkov instability with the intention of exposing the role of the equation of state. Results for Richtmyer-Meshkov instability in fluids with Mie-Gr�neisen equations of state derived from a linear shock-particle speed Hugoniot relationship (Jeanloz, J. Geophys. Res. 94, ...
We review experiments and calculations of the compressible Richtmyer-Meshkov instability from a single-mode, nonlinear initial perturbation. These experiments were performed using the Nova laser. Measurements of the time-evolution of the mixing region were reported previously. We compared the experimental measurements with numerical simulations [1,2]. We ...
The Richtmyer Meshkov instability of a low-Atwood-number miscible two-liquid system is investigated experimentally. The initially stratified fluids are contained within a rectangular tank mounted on a sled that rides on a vertical set of rails. The instability is generated by dropping the sled onto a coil spring, ...
This paper presents a numerical study of turbulent mixing due to the interaction of a shock wave with an inclined material interface. The interface between the two gases is modeled by geometrical random multimode perturbations represented by different surface perturbation power spectra with the same standard deviation. Simulations of the Richtmyer-Meshkov instability and ...
We present new velocity and density field measurements of a curtain of SF6 impacted by a Mach 1.2 shock and then reshocked by the reflected shock approximately 600 ?s after the initial shock impact. The initial conditions are those of a diffuse curtain of SF6 surrounded by air, and the interface is perturbed with a large-scale, single-mode, varicose perturbation. Statistical data are collected ...
A thin air-SF6-air gas curtain is impulsively accelerated by planar shock waves of varying strength (Mach 1.2-1.5) and investigated experimentally using simultaneous concentration field visualization and particle image velocimetry measurements. A novel nozzle design is used to create highly repeatable and flexible initial conditions that allow for isolation of effects on the flow structure due to ...
The Richtmyer-Meshkov (RM) instability is initiated by a shock accelerating an interface between two materials. Small perturbations of the interface grow into bubble and spike structures causing mixing of the materials that lie on either side of the interface. Recent Los Alamos National Laboratory experiments have focused on RM initiated mix in a compressible, miscible, ...
In this paper, we are concerned with physical aspects of three-dimensional Richtmyer-Meshkov instability (RMI) and resulting turbulent mixing phenomena in a convergent geometry. A system of two fluids, a heavy gas (sulfur hexafluoride, SF6) enclosed by a light gas (helium, He), is initially separated by two randomly perturbed interfaces. An artificial ...
In the standard Richtmyer-Meshkov instability, perturbations at a shocked interface grow after the passage of a shock. Freeze-out refers to the phenomenon whereby the perturbations do not grow, i.e., freeze-out, after the passage of a shock. This is fairly straightforward, at least theoretically (no experiments have been done so far) in a doubly shocked ...
Richtmyer-Meshkov instability of a thin curtain of heavy gas (SF6) embedded in air and accelerated by a planar shock wave (Mach 1.2) leads to the growth of interfacial perturbations in the curtain and to mixing. Our experiments produce a phenomenological description of the mixing transition and incipient turbulence during the first millisecond after the ...
In July 2009 we fielded three explosively (HE) driven Richtmyer-Meshkov instability experiments at the LANSCE Proton Radiography Facility (pRad), and in August of 2009 we fielded one flyer plate experiment on the pRad 40 mm powder gun. One HE experiment was done in vacuum, and the other two within four atmospheres of noble gasses: Xe and Ne. These two ...
In order to conduct Richtmyer-Meshkov instability experiments in shock accelerated thin liquid sheets, a light gas gun was designed and constructed at Marquette University. This paper contains the basic predictions and construction techniques utilized in the design and operation of a double diaphragm light gas gun. The compressed air gas gun is used to ...
The three-dimensional (3D) Richtmyer-Meshkov instability of incompressible, miscible liquids with a 3D single-mode initial perturbation is investigated. This study uses the apparatus of the earlier experiments of Niederhaus and Jacobs [J. Fluid Mech. 485, 243 (2003)] in which the instability is generated by impulsively accelerating a ...
We report on results of an experimental study of the Richtmyer- Meshkov instability. The growth of the mixing region in the nonlinear regime is measured for a set of cases in which the amplitude and wavelength of the initial perturbation are varied systematically. The experiments are conducted on the Nova laser facility, and use a Nova ...
Richtmyer-Meshkov (RM) instability occurs when a planar interface separating two fluids of different density is impulsively accelerated in the direction of its normal. It is one of the most fundamental fluid instabilities and is of importance to the fields of astrophysics and inertial confinement fusion. Because RM ...
Weighted essentially non-oscillatory (WENO) simulations of the reshocked two-dimensional single-mode Richtmyer-Meshkov instability using third-, fifth- and ninth-order spatial flux reconstruction and uniform grid resolutions corresponding to 128, 256 and 512 points per initial perturbation wavelength are presented. The dependence of the density, vorticity, ...
Finite-difference weighted essentially non-oscillatory (WENO) simulations of the reshocked two-dimensional single-mode Richtmyer-Meshkov instability using third-, fifth- and ninth-order spatial flux reconstruction and uniform spatial grid resolutions corresponding to 128, 256 and 512 points per initial perturbation wavelength are presented. The dependence ...
Motion of a fluid interface in Richtmyer-Meshkov instability is examined as a vortex sheet with the use of Birkhoff-Rott equation. This equation coupled with an evolution equation of the strength of the vortex sheet can describe all inviscid and incompressible fluid instabilities, i.e., Kelvin-Helmholtz, Rayleigh-Taylor, and Richtmyer-Meshkov ...
Previous work (Vold and Tomkins) compared computations to experiments for a shock driven interfacial instability (Richtmyer-Meshkov, R-M, instability) in a shocked gas cylinder. Mixing proceeds from an initially diffuse interface to a complex dipole vortex flow, then to a secondary instability with a characteristic ...
Flow instabilities are among the main issues of ICF studies. Heterogeneities of material or geometry are sources of instabilities which are strongly amplified in spherical geometries. According to the theory of Dyakov, some ranges of the Equation of State (EOS) also generate or amplify instabilities in shock waves, which can be ...
Richtmyer-Meshkov (RM) instability occurs when two different density fluids are impulsively accelerated in the direction normal to their nearly planar interface. The instability causes small perturbations on the interface to grow and eventually become a turbulent flow. It is closely related to Rayleigh-Taylor ...
... Accession Number : ADA521399. Title : Basic Hydrodynamics of Richtmyer- Meshkov-type Growth and Oscillations in the ICF-Relevant Conditions. ...
The National Ignition Facility. The Inertial Confinement. Fusion Concept. _I, Laser energy. Blowoff. Inward. trBnsported thermal energy. Atmosphere ...
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This paper addresses features of hydrodynamic instability growth on shock arrival at a free surface of condensed matter with deterministic initial perturbations. Richtmyer�Meshkov instability growth processes with initial two-dimensional (2D) and 3D perturbations are considered. Experimental diagnostics included pulsed radiography ...
The hydrocode SHAMRC has been used in the past to study the formation and growth of the Richtmyer Meshkov Instability (RMI). While RMI involves impulsively accelerating two continuous fluids of differing densities, a similar class of instabilities has been recently described for multiphase flow. In this scenario, a ...
Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, the results from a computational study of such a system under drive conditions to be attainable on the National Ignition Facility [E. M. Campbell, Laser Part. Beams 9, 209 (1991)] are presented. Using the ...
Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, we present the first results from a computational study of such a system under drive conditions to be attainable on the National Ignition Facility. Using the multiphysics, AMR, higher order Godunov ...
The ninth-order weighted essentially nonoscillatory (WENO) shock-capturing method is used to investigate the physics of reshock and mixing in two-dimensional single-mode Richtmyer-Meshkov instability to late times. The initial conditions and computational domain were adapted from the Mach 1.21 air (acetone)/ SF6 shock tube experiment of Collins and Jacobs ...
The ninth-order weighted essentially non-oscillatory (WENO) shock-capturing method is used to investigate the physics of reshock and mixing in two-dimensional single-mode Richtmyer-Meshkov instability to late times. The initial conditions and computational domain were adapted from the Mach 1.21 air(acetone)/SF{sub 6} shock tube experiment of Collins and ...
A numerical study of the evolution of the multimode planar Richtmyer-Meshkov instability (RMI) in a light-heavy (air-SF6, Atwood number A = 0.67) configuration involving a Mach number Ma = 1.5 shock is carried out. Our results demonstrate that the initial material interface morphology controls the evolution characteristics of RMI (for fixed A, Ma), and ...
The goal of the EZturb mix model in KULL is to predict the turbulent mixing process as it evolves from Rayleigh-Taylor, Richtmyer-Meshkov, or Kelvin-Helmholtz instabilities. In this report we focus on an example of the Richtmyer-Meshkov instability (which occurs when a shock hits an interface between fluids of different densities) with ...
The basis for the study of the evolution of a shocked interface stems from the question of the Rayleigh-Taylor (RT) instability (Taylor 1950). Starting in the late 18th century, the stability of an interface submitted to gravitational forces was investigated for the case in which the density of one of the materials across the interface was negligible compared to the other. ...
The response of a shock front to small preshock nonuniformities of density, pressure, and velocity is studied theoretically and numerically. These preshock nonuniformities emulate imperfections of a laser target, due either to its manufacturing, like joints or feeding tubes, or to preshock perturbation seeding/growth, as well as density fluctuations in foam targets, ''thermal ...
The Richtmyer-Meshkov instability after reshock is investigated in shock tube experiments at the Wisconsin Shock Tube Laboratory using planar laser imaging and a new high speed interface tracking technique. The interface is a 50-50% volume fraction mixture of helium and argon stratified over pure argon. This interface has an Atwood number of 0.29 and near single mode, ...
Results are presented from a series of shock tube experiments studying the Richtmyer-Meshkov instability (RMI) for the case of a 2-D single mode gas interface. The membraneless interface is formed by the head-on flow of nitrogen, seeded with acetone, and sulfur-hexafluoride which creates a stagnation surface. A sinusoidal interface is created by oscillating two rectangular ...
We investigate the mixing which occurs between a vertical cylinder of heavy gas (SF6) and the surrounding air before and after the passage of a weak planar shock front (Ma 1.2) normal to the cylinder axis. A goal is to understand the extent of molecular mixing at late times and to use the data to calibrate a multi-fluid diffusion model in a computational fluid dynamics code. The initial conditions ...
The single-mode Richtmyer-Meshkov hydrodynamic instability at light/heavy (air/SF6 and air/CO2), close density (air/N2), and heavy/light (air/He) interfaces has been experimentally studied for a low incident shock wave Mach number. Two identical 2D half sinusoidal initial perturbations, with a relatively high initial amplitude, were considered in order to ...
The process of implosion by inertial confinement is perturbed by hydrodynamic instabilities such as Rayleigh-Taylor, Richtmyer-Meshkov and Kelvin-Helmholtz instabilities. They may generate turbulent flow, causing the mixing of constituents and the degradation of the symmetry of the implosion. The authors extend Barenblatt`s study ...
We will describe two new advancements which have been made to the DRACO Lagrangian radiation-hydrodynamics code. First, the 3D hydrodynamics module has been validated using analytic formulas; second, we have added Implicit Monte Carlo (IMC) radiation transport in 2D r-z geometry. Previous results demonstrated the ability to model 3D Richtmyer-Meshkov (RM) ...
This paper describes a low energy flash X-ray system that is ideal for radiographing a wide variety of experimental phenomenon on both capacitor-bank pulsed power facilities and explosively driven magnetic-flux compression experiments. The versatility of this system has allowed us to obtain both single X-radiographs of imploding liners and multiple, temporally resolved radiographic sequences of ...
Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, results from three-dimensional (3D) numerical simulations of such a system under drive conditions to be attainable on the National Ignition Facility [E. M. Campbell, Laser Part. Beams 9, 209 (1991)] are ...
Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, results from three-dimensional numerical simulations of such a system under drive conditions to be attainable on the National Ignition Facility [E. M. Campbell, Laser Part. Beams, 9(2), 209 (1991)] are ...
Shock tube experiments have been undertaken in which a shock wave accelerates normally to an interface separating two gases of different densities leading to the formation of a three-dimensional mixing zone between the two gases. Assuming the mixing zone to be homogeneous and weakly dependent on the wall effects, an integrated monodirectional absorption technique had been previously carried out ...
The formally high-order, Eulerian, shock-capturing weighted essentially non-oscillatory (WENO) method is applied to a three- dimensional model of the Mach 1.5 air/SF6 Vetter-Sturtevant shock tube experiment with reshock. Results from fifth-, ninth- , and eleventh-order simulations are compared to quantitatively investigate the dependence of the dynamics and flow structure (including time-evolution ...
Recent work at LANL (Dimonte et al, Phys Fluids 2004, Ramaprabhu et al, JFM 2005) has shown that buoyancy-driven turbulence can be affected at late-time by initial conditions, and memory of the initial conditions is not lost. We study the initial condition parameters that impact the mixing and transition to turbulence in shock-driven, Richtmyer-Meshkov unstable flows. A ...
Recent observations of galaxy clusters show that temperatures of the intracluster medium (ICM) lie in the range of 10-100 million K. We would expect this gas to cool via radiative cooling; however, we do not observe this cooling. One way of keeping the ICM hot involves the coupling of jets emanating from supermassive black holes at the centers of galaxies within the cluster with the ICM. The ...
Experiments have been conducted in a vertical shock tube with a shock wave Mach number of 1.2. The two gases (air and SF6 with A = 0.66) are filled separately from the top and bottom ends of the shock tube, respectively. The gases then flow out of the tube through holes in the test section walls forming a slightly diffuse flat interface. Oscillating the flow inside of the tube generates a ...
Observations are presented from experiments and calculations where a laminar spherical CH4/air flame is perturbed successively by incident and reflected shock waves. The experiments are performed in a standard shock tube arrangement, in which a high-speed shadowgraph imaging system is used to record evolutions of the flame. Numerical simulations are conducted by using second-order wave propagation ...
In the large eddy simulation (LES) approach, large-scale energy-containing structures are resolved, smaller structures are filtered out, and unresolved subgrid effects are modeled. Extensive recent work has demonstrated that predictive under-resolved simulations of the velocity fields in turbulent flows are possible without resorting to explicit subgrid models, when using a class of ...
Carefully imposed initial conditions have been shown to control late time turbulence and mixing in buoyancy-driven flows [Dimonte et al., 2004; Banerjee & Andrews, 2009]. This is important in understanding and prediction of Inertial Confinement Fusion. We report the experimental results on the initial condition parameters, namely amplitude (?) and wavelength (?) of perturbations, that impact ...
The single- and multi-mode Richtmyer-Meshkov instabilities (RMI) with reshock are numerically analyzed in two- and three-dimensional domains. Four different types of air/SF 6 interface shapes are investigated in a shock tube configuration, and the predicted post-reshock growth rates are compared with available empirical models of Mikaelian's (Physica D ...
Supernova explosions are among the most dramatic in the universe. Type II supernovae follow core collapse of a massive star, while Type Ia supernovae are typically believed to be thermonuclear explosions of carbon-oxygen white dwarfs that have accreted enough material to initiate carbon burning. In both cases, the explosion dynamics are complicated by hydrodynamic ...
OAK-B135 An experimental investigation of a shock-induced interfacial instability (Richtmyer-Meshkov instability) is undertaken in an effort to study temporal evolution of interfacial perturbations in the late stages of development. The experiments are performed in a vertical shock tube with a square cross-section. A membraneless ...
Supernova (SN) 1987A focused attention on the critical role of hydrodynamic instabilities in the evolution of supernovae. To test the modeling of these instabilities, we are developing laboratory experiments of hydrodynamic mixing under conditions relevant to supernovae. Initial results were reported in J. Kane et al., Astrophys. J.478, L75 (1997) The Nova ...
Secondary instabilities on the organized, spanwise, vortical structures in incompressible shear layers, play an important role in generating the onset of three-dimensional turbulence in such flows. The effect of increasing compressibility on these instabilities is examined by using the compressible Stuart vortex as a model for a compressible shear layer. ...
Experimental and numerical results on the advance of a mixing or nonmixing front occurring at a density interface due to gravitational acceleration are analyzed considering the spectral structure of the front. The experimental configurations presented consists on an unstable two layer system held by a removable plate in a box for Rayleigh-Taylor instability driven fronts and a ...
It has been found previously that a thin (400-800�) high-Z overcoat on the laser side of the target can be effective in suppressing laser imprint [S. P. Obenschain et al. Phys. Plasmas 9, 2234 (2002)]. In those and subsequent experiments, it was found that the overcoat also results in an apparent delay in growth of a front-surface pre-imposed sinusoidal ripple without affecting the RT growth ...
The design of efficient, high-gain capsules for inertial confinement fusion (ICF) and the modeling of supernova implosions and explosions requires a detailed understanding of the consequences of material interpenetration, hydrodynamic instabilities and mixing at molecular (or atomic) scales arising from perturbations at material interfaces, i.e., the Rayleigh-Taylor, ...
The design of efficient, high-gain capsules for inertial confinement fusion (ICF), the modeling of supernova implosions and explosions, and the modeling of shock-induced mixing of multi-phase reactive energetic materials requires a detailed understanding of the consequences of material interpenetration, hydrodynamic instabilities and mixing at molecular (or atomic) scales ...
An expansion wave is produced when an incident shock wave interacts with a surface separating a fluid from a vacuum. Such an interaction starts the feedout process that transfers perturbations from the rippled inner (rear) to the outer (front) surface of a target in inertial confinement fusion. Being essentially a standing sonic wave superimposed on a centered expansion wave, a rippled expansion ...
The report presents the basic results of some calculations, theoretical and experimental efforts in the study of Rayleigh-Taylor, Kelvin-Helmholtz, Richtmyer-Meshkov instabilities and the turbulent mixing which is caused by their evolution. Since the late forties the VNIIEF has been conducting these investigations. This report is based on the data which ...
The structure of the concentration and velocity fields in a light-heavy-light fluid layer subjected to an impulsive acceleration by a shock wave (Richtmyer-Meshkov instability) is studied using simultaneous particle-image velocimetry and planar laser-induced fluorescence (PLIF) measurements (performed in such flows for the first time). The initial ...
An interface between gases with different acoustic impedance is prepared inside a vertical shock tube with square internal cross section using either of two approaches. In one case, a sinusoidally-shaped thin copper plate, initially separating a heavy from a light gas (with the light gas below the plate) is retracted from the shock tube; the Rayleigh-Taylor (RT) instability ...
The Richtmyer-Meshkov instability is studied for strongly shocked fluid interfaces in the nonlinear regime. An introduction to the instability is presented which includes important historical information as well as the motivation for pursuing the current research. A literature survey is conducted that covers the most relevant and recent work in the field, ...
In core-collapse supernovae, strong blast waves drive interfaces susceptible to Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) instabilities. In addition, perturbation growth can result from material expansion in large-scale velocity gradients behind the shock front. Laser-driven experiments are designed to produce a strongly ...
A major challenge in achieving ignition with double-shells is controlling the mix of the dense, high-Z pusher into the DT gas. During implosion, interface perturbations become unstable as they are subjected to either impulsive (Richtmyer-Meshkov) or time-dependent (Rayleigh-Taylor) accelerations. These processes are especially critical for double-shells since density gradient ...
Over the past several years we have presented a less than glowing experimental comparison of hydrodynamic codes with the gas curtain experiment. Here, we discuss the manner in which the various details of the hydrodynamic integration techniques conspire to produce poor results. This also includes some progress in improving the results and agreement with experimental results. Our results are based ...
For flows that contain significant structure, high order schemes offer large advantages over low order schemes. Fundamentally, the reason comes from the truncation error of the differencing operators. If one examines carefully the expression for the truncation error, one will see that for a fixed computational cost that the error can be made much smaller by increasing the numerical order than by ...
The validity of gradient-diffusion closures for modeling turbulent transport in multi-mode Rayleigh-Taylor and reshocked Richtmyer-Meshkov instability-induced mixing is investigated using data from three-dimensional spectral/tenth-order compact difference and ninth-order weighted essentially non-oscillatory simulations, respectively. Details on the ...
Recent experience on the Accelerated Strategic Computing Initiative (ASCI) computers shows that computational physicists are successfully producing a prodigious collection of numbers on several thousand processors. But with this wealth of numbers comes an unprecedented difficulty in processing and moving them to provide useful insight and analysis. In this talk, a few simulations are highlighted ...
We study shock-flame interactions on small scales as a possible mechanism for deflagration-to-detonation transition (DDT) in an exploding carbon-oxygen white dwarf. Thermonuclear flames are modeled using reactive Navier-Stokes equations coupled with a 13-species alpha-network. Two-dimensional numerical simulations that resolve carbon and oxygen burning scales show that shock-flame interactions ...
The cellular interactions during leukocyte margination and adhesion cascade in cardiovascular microcirculations are multi-scale and multiphysics phenomena, involving fluid flow, cell mechanics, chemical reaction kinetics and transport, fluid structure interaction. The vascular network in vivo has rather complicated topology unlike straight and flat channels and pipes where most biological ...
A new criterion, flow drive time, is identified here as a necessary condition for transition to turbulence in accelerated, unsteady flows. Compressible, high-Reynolds-number flows initiated, for example, in shock tubes, supersonic wind tunnels with practical limitations on dimensions or reservoir capacity, and high energy density pulsed laser target vaporization experimental facilities may not ...
Richtmyer-Meshkov instability (RMI) in gas-particle mixtures is investigated both numerically and analytically. The linear amplitude growth rate for a RMI in a two-phase mixture is derived by using a dusty gas formulation for small Stokes number (St<<1.0), and it is shown that the problem can be characterized by mass loading and St. The model ...
We present the first three-dimensional (3D) simulations of the large-scale mixing that takes place in the shock-heated stellar layers ejected in the explosion of a 15.5 M sun blue supergiant star. The blast is initiated and powered by neutrino-energy deposition behind the stalled shock by means of choosing sufficiently high neutrino luminosities from the contracting, nascent neutron star, whose ...
Relativistic astrophysical phenomena such as gamma-ray bursts (GRBs) and active galactic nuclei often require long-lived strong magnetic fields that cannot be achieved by shock compression alone. Here, we report on three-dimensional special-relativistic magnetohydrodynamic (MHD) simulations that we performed using a second-order Godunov-type conservative code to explore the amplification and decay ...
A major challenge in achieving ignition with double-shells is controlling the mix of the dense, high-Z pusher into the DT gas. During implosion, interface perturbations become unstable as they are subjected to either impulsive (Richtmyer-Meshkov) or time-...
Eulerian numerical schemes work well for smooth single-component hydrodynamic flow modeling. For multicomponent flows in compressible regimes, the emergence of large gradients in flow variables and the presence of material contacts degrade the quality of traditional Eulerian finite difference methods. Although higher order Godunov methods adequately capture shocks, artificial diffusion at contacts ...
Two-dimensional simulations of strongly anisotropic supernova explosions of a nonrotating 15 M? blue supergiant progenitor are presented, which follow the hydrodynamic evolution from times shortly after shock formation until hours later. It is shown that explosions which around the time of shock revival are dominated by low-order unstable modes (i.e. by a superposition of the l=2 and l=1 modes, in ...
Shock recovery experiments were conducted on suspensions of 106/ml E. coli bacteria contained in a water-based medium that is emplaced within stainless steel containers. The water is shocked and recovered. These experiments simulate the environment of bacteria residing either in surface bodies of water or in subsurface water-filled cracks in rocks. Early Earth life is likely to have existed in ...
In this article we develop an improved version of the classical fifth-order weighted essentially non-oscillatory finite difference scheme of [G.S. Jiang, C.W. Shu, Efficient implementation of weighted ENO schemes, J. Comput. Phys. 126 (1996) 202 228] (WENO-JS) for hyperbolic conservation laws. Through the novel use of a linear combination of the low order smoothness indicators already present in ...
... Taylor instability in laser ablatively accelerated targets for a fairly wide range of initial conditions. It is shown that the Rayleigh-Taylor growth rate in ...
It is not feasible to compute high Reynolds-number (Re) turbulent flows by directly resolving all scales of motion and material interfaces; instead, macroscale portions of the unsteady turbulent motion are computed while the rest of the flow physics including molecular diffusion and other micro scale physics (e.g., combustion) remains unresolved. In large eddy simulation (LES), the large energy ...
This report discusses topics on hydrodynamics instabilities in inertial confinement: linear analysis of Rayleigh-Taylor instability; ablation-surface instability; bubble rise in late-stage Rayleigh-Taylor instability; and saturation and multimode interactions in intermediate-stage ...
We present an analytical study of the linearized impulsive Richtmyer-Meshkov flow for incompressible elastic solids. Seminumerical prior investigations of a related shock-driven compressible elastic problem suggest that the interface amplitude remains bounded in time, in contrast to the unstable behavior found for gases. Our approach considers a base unperturbed flow and a ...
We experimentally investigate the evolution and interaction of two Richtmyer-Meshkov-unstable gas cylinders using concentration field visualization and particle image velocimetry. The heavy-gas (SF6) cylinders have an initial spanwise separation of S/D (where D is the cylinder diameter) and are simultaneously impacted by a planar, Mach 1.2 shock. The resulting flow ...
We report here experiments, conducted on the Omega laser [T.R. Boehly et al., Optics Commun. 133, 495 (1997)], and simulations that show reduced Richtmyer-Meshkov growth rates in a strongly shocked system with linear initial amplitudes (k{eta}{sub 0} {le} 0.9). The growth rate at early time is less than half the impulsive model prediction, rising at later time to near the ...
The authors introduce a fundamentally new time integration method for hyperbolic conservation laws based on self-adaptivity of the temporal method itself. The adaptivity is based upon the smoothness of the solution measured locally in time. Their approach can be contrasted with the usually global selection of a time integration methods and error-based time step selection methodology. A challenge ...
This report discusses topics on hydrodynamics instabilities in inertial confinement: linear analysis of Rayleigh-Taylor instability; ablation-surface instability; bubble rise in late-stage Rayleigh-Taylor instability; and saturation and multimode interact...
We review our recent contributions [1,2,3,4] in the light of their omission in recent publications [5,6,7,8]. Included is the VAVD process ( also called: secondary baroclinic circulation generation) which yields more positive and negative circulation through intermediate times than the original shock-accelerated vortex deposition (SAVD). VAVD is due to the acceleration provided by the rolled up ...
A laminated ablator is explored as an alternative concept for stabilizing the ablative Rayleigh-Taylor instability which develops in inertial fusion targets. Experiments measuring the growth of the Rayleigh-Taylor instability of laminated planar foils are reported. Consistent with both theory and simulations, a ...
This article presents a theory of these instabilities and potential modes of failure caused by them. Discussions are given for the following: small amplitude growth of the outside surface instability; and modes of failure resulting from nonlinear development of the inside surface instability.
... Accession Number : ADA129723. Title : Prospects for Optical Probing of the Rayleigh-Taylor Instability in Ablatively-Accelerated Foil Targets. ...
Linear theory of the ablative Rayleigh-Taylor instability in anisotropic diffusive materials is presented. This analysis indicates that enhancing diffusion in a plane transverse to the mean longitudinal flow can strongly reduce the growth of the instability. In the context of inertial confinement fusion, it is shown that anisotropic ...
We are concerned with the chaotic flow fields of turbulent mixing. Chaotic flow is found in an extreme form in multiply shocked Richtmyer--Meshkov unstable flows. The goal of a converged simulation for this problem is to obtain converged solutions for such micro solution features as the joint probability distributions of the temperature and species concentration, as well as ...
We present highly resolved concentration and PIV measurements of two interacting Richtmyer--Meshkov-unstable gas cylinders. The heavy-gas (SF_6) cylinders have an initial spanwise separation of S/D =3D 1.2 to 2.0, where D is the cylinder diameter. The resulting flow morphologies are observed to be highly sensitive to the separation, and vorticity fields reveal that a principal ...
I review how the discipline of ``nonlinear'' physics arose from the '54-`55 Fermi-Pasta-Ulam (FPU) digital computer simulations of the nonlinear one-dimensional alpha-lattice and the discovery of the soliton (1965) and ``n-curve'' states (1967). Recently, applications to accelerated inhomogeneous (Richtmyer-Meshkov) flows have been made and evolving vortex bilayers and ...
We explore the nature of shock-turbulence interaction in three configurations: forced compressible isotropic turbulence, isotropic and anisotropic turbulence passing through a planar shock. The last problem is relevant to the turbulence changes during the re-shock in a classical Richtmyer-Meshkov problem. Results from direct numerical simulations are used to examine the ...
... developed in the target after the shock ... INSTABILITY, COMPUTERIZED SIMULATION, LASER BEAMS. Subject Categories : LASERS AND MASERS ...
The main characteristics of the linear Darrieus-Landau instability in the laser ablation flow are investigated. The dispersion relation of the instability is found numerically as a solution to an eigenvalue stability problem, taking into account the continuous structure of the flow. The results are compared to the classical ...
A mathematical method for a fully self-consistent treatment of the Rayleigh--Taylor instability is developed by solving the linearized fluid equations as an eigenvalue problem. The method is applied to analyze the instability in stationary ablating plasmas with strong inhomogeneity. A reduction of growth rate compared to the classical ...
The results of the experiments carried out on a laser system are reported. The work is performed in order to investigate the problem of target instability under ablative acceleration and to get direct evidence of Rayleigh-Taylor instabilities. Tri-layer e...
Richtmyer-Meshkov (RM) mixing seeded by multimode initial surface perturbations in a convergent, compressible, miscible plasma system is measured on the OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] laser system. A strong shock (Mach 12-20), created by 50 laser beams, is used to accelerate impulsively a thin aluminum shell into a lower density foam. As the system ...
We present the results of a series of detailed numerical simulations of the Rayleigh-Taylor instability in laser ablatively accelerated targets for a fairly wide range of initial conditions. It is shown that the Rayleigh-Taylor growth rate in an ablative ...
The highly nonlinear evolution of the single-mode Rayleigh-Taylor instability (RTI) at the ablation front of an accelerated target is investigated in the parameter range typical of inertial confinement fusion implosions. A new phase of the nonlinear bubble evolution is discovered. After the linear growth phase and a short constant-velocity phase, it is ...
The evolution of the Rayleigh-Taylor (RT) instability in a compressible medium was investigated both at an accelerating embedded interface and at the ablation front in a new series of experiments on Nova. The x-ray drive generated in a hohlraum ablatively...
A fully nonlinear sharp-boundary model of the ablative Rayleigh-Taylor instability is derived and closed in a similar way to the self-consistent closure of the linear theory. It contains the stabilizing effect of ablation and accurately reproduces the results of 2D DRACO simulations. The single-mode saturation amplitude, bubble and ...
A weakly nonlinear model is proposed for the Rayleigh-Taylor instability in presence of ablation and thermal transport. The nonlinear effects for a single-mode disturbance are computed, included the nonlinear correction to the exponential growth of the fundamental modulation. Mode coupling in the spectrum of a multimode disturbance is thoroughly analyzed ...
