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  • 1
    Electronic Resource
    Electronic Resource
    Finite Larmor radius stabilization of the Rayleigh–Taylor turbulent mixing width (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 499-500 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A diffusion model for turbulent mix [C. Cherfils and K. O. Mikaelian, Phys. Fluids 8, 522 (1996)] is compared with recent two-dimensional magnetohydrodynamic simulations by Huba [Phys. Plasmas 3, 2523 (1996)]. The model accounts for density gradient stabilization and for finite Larmor radius stabilization, thus suppressing the Rayleigh–Taylor mixing width to below its classical value. The model, which has no free parameters, appears to be in good agreement with Huba's numerical simulations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872108
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  • 2
    Electronic Resource
    Electronic Resource
    Density gradient stabilization of the Richtmyer–Meshkov instability (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2638-2643 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical and analytical results on the growth rate of the Richtmyer–Meshkov (RM) instability in continuous density profiles are presented, and this paper relates them to the Rayleigh–Taylor (RT) instability by treating the shock as an instantaneous acceleration of incompressible fluids. Most of this work is in the linear regime, where it is found that density gradient stabilization is even more effective for the RM instability than for the RT instability. Recent experimental results are discussed and a numerical simulation of a shock-tube experiment with a continuous density profile between two gases is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858152
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  • 3
    Electronic Resource
    Electronic Resource
    Numerical simulations of Richtmyer–Meshkov instabilities in finite-thickness fluid layers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 1269-1292 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct numerical simulations of Richtmyer–Meshkov instabilities in shocked fluid layers are reported and compared with analytic theory. To investigate new phenomena such as freeze-out, interface coupling, and feedthrough, several new configurations are simulated on a two-dimensional hydrocode. The basic system is an A/B/A combination, where A is air and B is a finite-thickness layer of freon, SF6, or helium. The middle layer B has perturbations either on its upstream or downstream side, or on both sides, in which case the perturbations may be in phase (sinuous) or out of phase (varicose). The evolution of such perturbations under a Mach 1.5 shock is calculated, including the effect of a reshock. Recently reported gas curtain experiments [J. M. Budzinski et al., Phys. Fluids 6, 3510 (1994)] are also simulated and the code results are found to agree very well with the experiments. A new gas curtain configuration is also considered, involving an initially sinuous SF6 or helium layer and a new pattern, opposite mushrooms, is predicted to emerge. Upon reshock a relatively simple sinuous gas curtain is found to evolve into a highly complex pattern of nested mushrooms. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868898
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetic energy of Rayleigh–Taylor and Richtmyer–Meshkov instabilities (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2625-2637 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: General expressions for the kinetic energy associated with Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) instabilities in incompressible fluids are derived. The results are valid for small perturbations in continuous as well as discontinuous density profiles. It was found that KERT /KERM=ge2γτ /(ΔvΓ)2=(geγτ/Δvγ)2, where τ=time, g=acceleration, Δv=velocity jump, and γ is the exponential growth rate of the RT amplitude. The linear growth rate of the RM amplitude is ΔvΓ2=Δvγ2/g, and is found by solving an eigenvalue equation for a given density profile subject to appropriate boundary conditions. In general, KERT asymptotes to a constant value at large k (k=2π/λ, λ=wavelength), while KERM continues to grow with k. Several analytic examples are illustrated and the k dependence of the kinetic energies is displayed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858151
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  • 5
    Electronic Resource
    Electronic Resource
    Oblique shocks and the combined Rayleigh–Taylor, Kelvin–Helmholtz, and Richtmyer–Meshkov instabilities (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 1943-1945 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This Letter considers the evolution of perturbations at an interface between two fluids subjected to an oblique shock. The normal component of the shock generates the Richtmyer–Meshkov (RM) instability, and the parallel component generates the Kelvin–Helmholtz (KH) instability. If a constant normal acceleration is also present it induces the Rayleigh–Taylor (RT) instability or, depending on the sign of gA (g=acceleration, A=Atwood number), it acts to stabilize the KH and RM instabilities. Treating the shock as an instantaneous acceleration, analytic formulas are derived for the evolution of the perturbations. This Letter illustrates with an application to inertial-confinement-fusion capsules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868198
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  • 6
    Electronic Resource
    Electronic Resource
    Rayleigh–Taylor and Richtmyer–Meshkov instabilities in finite-thickness fluid layers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 888-890 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) instabilities are considered in a fluid layer of thickness t having perturbations of arbitrary wave number k at either one or both interfaces. The evolution of the perturbation amplitudes η1,2(τ), τ =time, is given analytically in terms of a coupling angle θ which measures the strength of the coupling between interfaces 1 and 2. A new type of freeze-out in shocked layers is reported according to which, the proximity of the two interfaces can, under proper conditions, lead to the complete freeze-out of one, but not both, perturbations. For example, to freeze the first interface one needs η1(0)/η2(0)= sin θ. Freeze-out cannot be achieved in the RT case; instead, one can kill one of the modes. For example, setting η1(0)/η2(0)= tan(θ/2) will kill the exponentially growing mode, leaving only the oscillatory mode at both interfaces. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868611
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  • 7
    Electronic Resource
    Electronic Resource
    Freeze-out and the effect of compressibility in the Richtmyer–Meshkov instability (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 356-368 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Perturbations of small-amplitude η at the interface between two fluids grow linearly in time after the passage of a shock. According to Richtmyer's prescription, the growth rate is proportional to the Atwood number after the interface has been shocked, η(overdot)∼Aafter. The focus is on highly compressible fluids starting with Abefore≥0. By carrying out two-dimensional numerical simulations, several exceptions to Richtmyer's prescription are found, in particular, when Aafter≤0. Neither the expected freeze-out when Aafter=0 nor the phase reversal when Aafter〈0 is observed. The results, however, are in agreement with Fraley's analysis, which is compared and contrasted with Richtmyer's prescription. Previous calculations and experiments on the Richtmyer–Meshkov instability are analyzed, it is explained why they have not detected the failure of Richtmyer's prescription, and several new numerical and physical experiments are proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868091
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  • 8
    Electronic Resource
    Electronic Resource
    Turbulent energy at accelerating and shocked interfaces (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 592-598 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The turbulent energy generated at accelerating or shocked interfaces between two fluids is calculated. Assuming a linear density profile across the mix region it was found that Eturb/Edir=2.3A2% for a constant acceleration and 9.3A2% for a shock, where A is the Atwood number of the two fluids. Somewhat less turbulent energy is generated if density profiles based on self-similar solutions to nonlinear diffusion equations were used. These equations also predict eddy sizes: λ/h=26%–29% and λ/h=16%–18% were found for a constant acceleration and a shock, respectively, where λ is the eddy size controlling the diffusion coefficient and h is the mixing depth into the heavier fluid. The present results were compared with other models and with experiments conducted at AWE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857759
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  • 9
    Electronic Resource
    Electronic Resource
    Simple model for the turbulent mixing width at an ablating surface (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 522-535 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A diffusion model is applied to calculate the turbulent mixing width at an ablating surface. It is proposed that the general model be tested first on well-determined and easily accessible stabilizing mechanisms such as surface tension, viscosity, density gradient, or finite thickness. In this model the turbulent mixing width h is directly correlated with the growth rate γ of the perturbations in the presence of stabilizing mechanisms: h/hclass=(γ/γclass)1/2, where hclass=0.07 Agτ2 and γclass=(square root of)Agk (where A is the Atwood number, g is the acceleration, τ is the time, and k =2π/λ =2π/(ωhclass), ω being a dimensionless constant in the model). The method is illustrated with several examples for hablation, each based on a different γablation. Direct numerical simulations are presented comparing h with and without density gradients. In addition to mixing due to the Rayleigh–Taylor instability, the diffusion model is applied to the Kelvin–Helmholtz and the Richtmyer–Meshkov mixing layers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868805
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  • 10
    Electronic Resource
    Electronic Resource
    Turbulent energy at an ablating surface (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 964-968 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We calculate the turbulent energy generated at a surface which is accelerating by ablation. The ablation velocity Va reduces the growth rate n(k) from its classical value for the Rayleigh–Taylor instability. This reduction is reflected in our general expression for Eturbulent, valid for arbitrary Va, which we derive on the basis of the Canuto–Goldman model for turbulence [Phys. Rev. Lett. 54, 430 (1985)]. Out results are analytic and they reduce to particularly simple forms in the classical (Va→0) and strongly inhibited (Va→∞) limits, where we find Eturbulent=(2/3)(56/9π)2Ag/k0 and Eturbulent=(8Ag/3πk0Va)2, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342999
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