scholarly journals Rarefaction-driven Rayleigh–Taylor instability. Part 2. Experiments and simulations in the nonlinear regime

2018 ◽  
Vol 838 ◽  
pp. 320-355 ◽  
Author(s):  
R. V. Morgan ◽  
W. H. Cabot ◽  
J. A. Greenough ◽  
J. W. Jacobs
Keyword(s):  
Rarefaction Wave ◽  
Three Dimensional ◽  
Single Mode ◽  
Taylor Instability ◽  
Nonlinear Regime ◽  
Diffuse Interface ◽  
Late Time ◽  
Two Dimensional ◽  
Rayleigh Taylor Instability ◽  
Atwood Number

Experiments and large eddy simulation (LES) were performed to study the development of the Rayleigh–Taylor instability into the saturated, nonlinear regime, produced between two gases accelerated by a rarefaction wave. Single-mode two-dimensional, and single-mode three-dimensional initial perturbations were introduced on the diffuse interface between the two gases prior to acceleration. The rarefaction wave imparts a non-constant acceleration, and a time decreasing Atwood number, $A=(\unicode[STIX]{x1D70C}_{2}-\unicode[STIX]{x1D70C}_{1})/(\unicode[STIX]{x1D70C}_{2}+\unicode[STIX]{x1D70C}_{1})$, where $\unicode[STIX]{x1D70C}_{2}$ and $\unicode[STIX]{x1D70C}_{1}$ are the densities of the heavy and light gas, respectively. Experiments and simulations are presented for initial Atwood numbers of $A=0.49$, $A=0.63$, $A=0.82$ and $A=0.94$. Nominally two-dimensional (2-D) experiments (initiated with nearly 2-D perturbations) and 2-D simulations are observed to approach an intermediate-time velocity plateau that is in disagreement with the late-time velocity obtained from the incompressible model of Goncharov (Phys. Rev. Lett., vol. 88, 2002, 134502). Reacceleration from an intermediate velocity is observed for 2-D bubbles in large wavenumber, $k=2\unicode[STIX]{x03C0}/\unicode[STIX]{x1D706}=0.247~\text{mm}^{-1}$, experiments and simulations, where $\unicode[STIX]{x1D706}$ is the wavelength of the initial perturbation. At moderate Atwood numbers, the bubble and spike velocities approach larger values than those predicted by Goncharov’s model. These late-time velocity trends are predicted well by numerical simulations using the LLNL Miranda code, and by the 2009 model of Mikaelian (Phys. Fluids., vol. 21, 2009, 024103) that extends Layzer type models to variable acceleration and density. Large Atwood number experiments show a delayed roll up, and exhibit a free-fall like behaviour. Finally, experiments initiated with three-dimensional perturbations tend to agree better with models and a simulation using the LLNL Ares code initiated with an axisymmetric rather than Cartesian symmetry.

scholarly journals Rarefaction-driven Rayleigh–Taylor instability. Part 1. Diffuse-interface linear stability measurements and theory

2016 ◽  
Vol 791 ◽  
pp. 34-60 ◽  
Author(s):  
R. V. Morgan ◽  
O. A. Likhachev ◽  
J. W. Jacobs
Keyword(s):  
Linear Stability ◽  
Rarefaction Wave ◽  
Diffusion Model ◽  
Growth Rates ◽  
Three Dimensional ◽  
Mie Scattering ◽  
Taylor Instability ◽  
Diffuse Interface ◽  
Rayleigh Taylor Instability ◽  
Dynamic Diffusion

Theory and experiments are reported that explore the behaviour of the Rayleigh–Taylor instability initiated with a diffuse interface. Experiments are performed in which an interface between two gases of differing density is made unstable by acceleration generated by a rarefaction wave. Well-controlled, diffuse, two-dimensional and three-dimensional, single-mode perturbations are generated by oscillating the gases either side to side, or vertically for the three-dimensional perturbations. The puncturing of a diaphragm separating a vacuum tank beneath the test section generates a rarefaction wave that travels upwards and accelerates the interface downwards. This rarefaction wave generates a large, but non-constant, acceleration of the order of $1000g_{0}$, where $g_{0}$ is the acceleration due to gravity. Initial interface thicknesses are measured using a Rayleigh scattering diagnostic and the instability is visualized using planar laser-induced Mie scattering. Growth rates agree well with theoretical values, and with the inviscid, dynamic diffusion model of Duff et al. (Phys. Fluids, vol. 5, 1962, pp. 417–425) when diffusion thickness is accounted for, and the acceleration is weighted using inviscid Rayleigh–Taylor theory. The linear stability formulation of Chandrasekhar (Proc. Camb. Phil. Soc., vol. 51, 1955, pp. 162–178) is solved numerically with an error function diffusion profile using the Riccati method. This technique exhibits good agreement with the dynamic diffusion model of Duff et al. for small wavenumbers, but produces larger growth rates for large-wavenumber perturbations. Asymptotic analysis shows a $1/k^{2}$ decay in growth rates as $k\rightarrow \infty$ for large-wavenumber perturbations.

scholarly journals Three-dimensional simulations and analysis of the nonlinear stage of the Rayleigh-Taylor instability

1995 ◽  
Vol 13 (3) ◽  
pp. 423-440 ◽  
Author(s):  
J. Hecht ◽  
D. Ofer ◽  
U. Alon ◽  
D. Shvarts ◽  
S.A. Orszag ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Three Dimensional ◽  
Spherical Geometry ◽  
Taylor Instability ◽  
Three Dimensions ◽  
Type Model ◽  
Late Time ◽  
Nonlinear Stage ◽  
Rayleigh Taylor Instability ◽  
Atwood Number

The nonlinear stage in the growth of the Rayleigh-Taylor instability in three dimensions (3D) is studied using a 3D multimaterial hydrodynamic code. The growth of a single classical 3D square and rectangular modes is compared to the growth in planar and cylindrical geometries and found to be close to the corresponding cylindrical mode, which is in agreement with a new Layzer-type model for 3D bubble growth. The Atwood number effect on the final shape of the instability is demonstrated. Calculations in spherical geometry of the late deceleration stage of a typical ICF pellet have been performed. The different late time shapes obtained are shown to be a result of the initial conditions and the high Atwood number. Finally, preliminary results of calculations of two-mode coupling and random perturbations growth in 3D are presented.

scholarly journals A Relaxation Filtering Approach for Two-Dimensional Rayleigh–Taylor Instability-Induced Flows

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 78 ◽  
Author(s):  
Sk. Mashfiqur Rahman ◽  
Omer San
Keyword(s):  
High Resolution ◽  
Numerical Experiments ◽  
Single Mode ◽  
Taylor Instability ◽  
Two Dimensional ◽  
Reconstruction Scheme ◽  
Rayleigh Taylor Instability ◽  
Multi Mode ◽  
Filtering Approach ◽  
Point Stencil

In this paper, we investigate the performance of a relaxation filtering approach for the Euler turbulence using a central seven-point stencil reconstruction scheme. High-resolution numerical experiments are performed for both multi-mode and single-mode

scholarly journals Arbitrary Lagrange–Eulerian code simulations of turbulent Rayleigh–Taylor instability in two and three dimensions

2003 ◽  
Vol 21 (3) ◽  
pp. 455-461 ◽  
Author(s):  
S.V. WEBER ◽  
G. DIMONTE ◽  
M.M. MARINAK
Keyword(s):  
Linear Growth ◽  
Three Dimensional ◽  
Taylor Instability ◽  
Three Dimensions ◽  
Two Dimensional ◽  
Grid Refinement ◽  
Group Code ◽  
Interface Reconstruction ◽  
Intercomparison Project ◽  
Rayleigh Taylor Instability

We have performed simulations of the evolution of the turbulent Rayleigh–Taylor instability with an arbitrary Lagrange–Eulerian code. The problem specification was defined by Dimonteet al.(2003) for the “alpha group” code intercomparison project. Perfect γ = 5/3 gases of densities 1 and 3 g/cm3are accelerated by constant gravity. The nominal problem uses a 2562× 512 mesh with initial random multiwavelength interface perturbations. We have also run three-dimensional problems with smaller meshes and two-dimensional (2D) problems of several mesh sizes. Under-resolution lowered linear growth rates of the seed modes to 5-60% of the analytic values, depending on wavelength and orientation to the mesh. However, the mix extent in the 2D simulations changed little with grid refinement. Simulations without interface reconstruction gave penetration only slightly reduced from the case with interface reconstruction. Energy dissipation differs little between the two cases. The slope of the penetration distance versus time squared, corresponding to the α parameter inh= αAgt2, decreases with increasing time in these simulations. The slope, α, is consistent with the linear electric motor data of Dimonte and Schneider (2000), but the growth is delayed in time.

scholarly journals Three-dimensional single-mode nonlinear ablative Rayleigh-Taylor instability

2016 ◽  
Vol 23 (2) ◽  
pp. 022701 ◽  
Author(s):  
R. Yan ◽  
R. Betti ◽  
J. Sanz ◽  
H. Aluie ◽  
B. Liu ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Single Mode ◽  
Taylor Instability ◽  
Rayleigh Taylor Instability

scholarly journals Experiments and Simulations on the Turbulent, Rarefaction Wave Driven Rayleigh–Taylor Instability

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
R. V. Morgan ◽  
J. W. Jacobs
Keyword(s):  
Rarefaction Wave ◽  
Lawrence Livermore National Laboratory ◽  
National Laboratory ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Quantitative Agreement ◽  
Diffuse Interface ◽  
Diffusion Layer Thickness ◽  
Average Value ◽  
Rayleigh Taylor Instability

Abstract Experiments were performed to observe the growth of the turbulent, Rayleigh–Taylor unstable mixing layer generated between air and SF6, with an Atwood number of A=(ρ2−ρ1)/(ρ2+ρ1)=0.64, where ρ1 and ρ2 are the densities of air and SF6, respectively. A nonconstant acceleration with an average value of 2300g0, where g0 is the acceleration due to gravity, was generated by interaction of the interface between the two gases with a rarefaction wave. Three-dimensional, multimode perturbations were generated on the diffuse interface, with a diffusion layer thickness of δ=3.6 mm, using a membraneless vertical oscillation technique, and 20 experiments were performed to establish a statistical ensemble. The average perturbation from this ensemble was extracted and used as input for a numerical simulation using the Lawrence Livermore National Laboratory (LLNL) Miranda code. Good qualitative agreement between the experiment and simulation was observed, while quantitative agreement was best at early to intermediate times. Several methods were used to extract the turbulent growth constant α from experiments and simulations while accounting for time varying acceleration. Experimental, average bubble and spike asymptotic self-similar growth rate values range from α=0.022 to α=0.032 depending on the method used, and accounting for variable acceleration. Values found from the simulations range from α=0.024 to α=0.041. Values of α measured in the experiments are lower than what are typically measured in the literature but are more in line with those found in recent simulations.

Design of a single-mode Rayleigh–Taylor instability experiment in the highly nonlinear regime

2019 ◽  
Vol 32 ◽  
pp. 18-30
Author(s):  
G. Malamud ◽  
L. Elgin ◽  
T. Handy ◽  
C. Huntington ◽  
R.P. Drake ◽  
...  
Keyword(s):  
Single Mode ◽  
Taylor Instability ◽  
Nonlinear Regime ◽  
Highly Nonlinear ◽  
Rayleigh Taylor Instability
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