Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session L19: Rayleigh Taylor Instability II |
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Chair: Snezhana Abarzhi, University of Chicago Room: 322 |
Monday, November 21, 2011 3:35PM - 3:48PM |
L19.00001: One-dimensional-turbulence simulations of reactive Rayleigh-Taylor turbulence Esteban Gonzalez, Alan Kerstein, David Lignell We consider the problem of reactive Rayleigh-Taylor turbulence in the Boussinesq framework, and model combustion with a reaction-progress-variable method, and a KPP reaction. The interesting feature of this problem is that the interface (flame) between heavy/cold reactants and light/hot products moves against gravity. Such problem is challenging because of the delicate interplay between turbulence, buoyancy, and reactions, and the wide separation between large and small scales. One model that has the capabilities to deal with these challenges is the one-dimensional-turbulence (ODT) model. In this talk, we discuss ODT results for non-reactive and reactive Rayleigh-Taylor turbulence, and compare them with those from direct numerical simulations (DNS). Here, the key advantage of ODT over DNS is that it can be used to explore larger parameter spaces. [Preview Abstract] |
Monday, November 21, 2011 3:48PM - 4:01PM |
L19.00002: Late-time evolution of Rayleigh-Taylor instability in a domain of a finite size Snezhana Abarzhi For the first time a theoretical analysis was developed to systematically study the late-time evolution of Rayleigh-Taylor instability in a domain of a finite size. The nonlinear dynamics of fluids with similar and contrasting densities are considered for two-dimensional and three-dimensional flows driven by sustained or time-dependent acceleration. The flows are periodic in the plane normal to the direction of acceleration and have no external mass sources. Group theory analysis is applied to accurately account for the mode coupling. Asymptotic nonlinear solutions are found to describe the interface dynamics far from the boundaries and near the boundaries. The influence of the size of the domain on the diagnostic parameters of the flow is identified. In particular, it is shown that in a finite size the domain the flow is decelerating compared to spatially extended case. The theory outcomes for the numerical modeling and design of experiments on Rayleigh-Taylor instability are discussed. [Preview Abstract] |
Monday, November 21, 2011 4:01PM - 4:14PM |
L19.00003: Reynolds--Averaged Navier--Stokes Modeling of Large Reynolds Number Mechanical and Scalar Rayleigh--Taylor Turbulent Mixing Gregory Burton, Oleg Schilling A three- and four-equation, variable-density, incompressible Reynolds-averaged Navier--Stokes model incorporating mechanical and scalar turbulence is used to simulate Rayleigh--Taylor turbulent mixing with an Atwood number equal to one-half. Using both Reynolds number-dependent (optimal) and constant late-time model coefficients obtained by minimizing the $L^2$ norm between the model and the large Reynolds number $3072^3$ Cabot--Cook direct numerical simulation data, the predicted mixing layer evolution is compared with the averaged DNS data in a posteriori tests. The terms in the transport equation budgets are compared in detail to their profiles across the mixing layer predicted by the DNS. The capability of the model to predict the degree of molecular mixing is also assessed. [Preview Abstract] |
Monday, November 21, 2011 4:14PM - 4:27PM |
L19.00004: ABSTRACT WITHDRAWN |
Monday, November 21, 2011 4:27PM - 4:40PM |
L19.00005: Turbulent Rayleigh-Taylor flow driven by time-varying accelerations Praveen Ramaprabhu, Andrew Lawrie, Karthik Muthuraman We report on numerical simulations of turbulent Rayleigh-Taylor flow subject to variable acceleration histories. The acceleration profiles were inspired by experiments and theoretical studies, and include an impulsive acceleration, accel-decel profiles, as well as a constant drive as the baseline case. The simulations were performed using the MOBILE software, a variable-density, incompressible fluid flow code. The advection algorithm employs a 3$^{rd}$-order, monotonicity-preserving upwind scheme, allowing the definition of sharp interfaces in the flow, while pressure convergence is accelerated by the use of a multi-grid scheme. The simulations are initialized with two classes of perturbations: narrow-band, short-wavelength modes and broadband with long-wavelength modes. The effect of initial amplitudes on the perturbations is investigated under the variable drive conditions. The acceleration profiles are capable of producing stages of ``demixing,'' useful in validating turbulence models of RTI. [Preview Abstract] |
Monday, November 21, 2011 4:40PM - 4:53PM |
L19.00006: Direct Numerical Simulations of Rayleigh-Taylor instability Daniel Livescu, Tie Wei, Mark Petersen The development of the Rayleigh-Taylor mixing layer is studied using data from an extensive new set of Direct Numerical Simulations (DNS). This includes a suite of simulations with grid size of $1024^2 \times 4608$ and Atwood number ranging from A=0.04 to 0.9, in order to examine small departures from the Boussinesq approximation as well as large Atwood number effects, and a high resolution simulation of grid size $4096^2 \times 4032$ and Atwood number of 0.75. After the layer width had developed substantially, additional branched simulations have been run under reversed and zero gravity conditions. The results presented address the role of the initial conditions on the mixing layer development and the discrepancy between the growth rates in various experiments and numerical simulations, as well as the changes in Rayleigh-Taylor turbulence properties at large density ratios. [Preview Abstract] |
Monday, November 21, 2011 4:53PM - 5:06PM |
L19.00007: Simulations of Compressible Rayleigh-Taylor Instability Using the Adaptive Wavelet Collocation Method Scott J. Reckinger, Daniel Livescu, Oleg V. Vasilyev Numerical simulations of the single-mode compressible Rayleigh-Taylor instability are performed on an adaptive mesh using the Adaptive Wavelet Collocation Method (AWCM). Due to the physics-based adaptivity and direct error control of the method, AWCM is ideal for resolving the wide range of scales present in the development of the instability. The problem is initialized consistent with the solutions from linear stability theory, with two diffusively mixed, stratified fluids of differing molar masses as the background state. Of interest are the compressibility effects on the departure time from the linear growth, the onset of strong non-linear interactions, and the late-time behavior of the fluid structures. The late time bubble and spike velocities are computed and compared to those obtained in the incompressible case. [Preview Abstract] |
Monday, November 21, 2011 5:06PM - 5:19PM |
L19.00008: ABSTRACT WITHDRAWN |
Monday, November 21, 2011 5:19PM - 5:32PM |
L19.00009: On Buoyancy and Shear Mixing Beth Placette, Bhanesh Akula, Malcolm Andrews, Devesh Ranjan Combined Rayleigh Taylor and Kelvin Helmholtz instabilities play a significant role in a number of phenomena, most importantly inertial confinement fusion. Should the relationship between initial conditions and mixing be determined, then, in principle, the level of mixing could be controlled through the setting of specific conditions. To investigate this proposition, a Kelvin Helmholtz Rayleigh Taylor experiment with a low Atwood number, buoyancy- and velocity-driven mixing width was investigated. The experiment was modeled using an implicit large eddy simulation code which uses a finite volume technique to solve the three dimensional incompressible Euler equations. The number of modes and the magnitude of the perturbations were set to investigate the rate of development as well as the maximum growth reached of the mixing width. Preliminary results show a promising overall agreement for the mixed region when the number of modes is increased. [Preview Abstract] |
Monday, November 21, 2011 5:32PM - 5:45PM |
L19.00010: Direct Numerical Simulation of Tilted Rayleigh-Taylor Instability Tie Wei, Daniel Livescu The tilted Rayleigh-Taylor instability, where the initial interface is not perpendicular to the driving acceleration, is investigated using Direct Numerical Simulations (DNS). In this configuration, the inclination of the initial interface results in a large-scale overturning motion in addition to the buoyancy driven instability. The DNS results are compared to the rocket-rig experiments of Smeeton and Youngs (AWE Report No. 35/87) at several Atwood numbers (A=0.267, 0.48, and 0.90). Since the initial conditions in these experiments are largely unknown, an extensive range of initial conditions have been explored to match the mixing layer growth between DNS and experiments. The evolution of the mixing layer was found to be strongly influenced, for the duration of the experiments, by the initial spectrum shape and peak location, as well as the perturbation amplitude. A set of initial conditions matching the experimental growth rates has been determined. Results are also presented on the interaction between shear and buoyancy, including the parameters influencing the overturning and mixing. [Preview Abstract] |
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