scholarly journals Rayleigh–Taylor Instability With Varying Periods of Zero Acceleration

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Denis Aslangil ◽  
Zachary Farley ◽  
Andrew G. W. Lawrie ◽  
Arindam Banerjee
Keyword(s):  
Numerical Investigation ◽  
Structural Changes ◽  
Mixing Layer ◽  
Taylor Instability ◽  
Scaling Exponent ◽  
External Forcing ◽  
Acceleration Field ◽  
Rayleigh Taylor Instability

Abstract We present our findings from a numerical investigation of the acceleration-driven Rayleigh–Taylor Instability, modulated by varying periods without an applied acceleration field. It is well known from studies on shock-driven Richtmyer–Meshkov instability that mixing without external forcing grows with a scaling exponent as ≈t0.20−0.28. When the Rayleigh–Taylor Instability is subjected to varying periods of “zero” acceleration, the structural changes to the mixing layer remain remarkably small. After the acceleration is re-applied, the mixing layer quickly resumes the profile of development it would have had if there had been no intermission. This behavior contrasts in particular with the strong sensitivity that is found to other variable acceleration profiles examined previously in the literature.

scholarly journals The effects of forced small-wavelength, finite-bandwidth initial perturbations and miscibility on the turbulent Rayleigh–Taylor instability

2015 ◽  
Vol 787 ◽  
pp. 50-83 ◽  
Author(s):  
M. S. Roberts ◽  
J. W. Jacobs
Keyword(s):  
High Speed ◽  
Initial Perturbation ◽  
Mixing Layer ◽  
Experimental Studies ◽  
Growth Parameter ◽  
Video Camera ◽  
Taylor Instability ◽  
Layer Width ◽  
High Speed Video Camera ◽  
Rayleigh Taylor Instability

Rayleigh–Taylor instability experiments are performed using both immiscible and miscible incompressible liquid combinations having a relatively large Atwood number of $A\equiv ({\it\rho}_{2}-{\it\rho}_{1})/({\it\rho}_{2}+{\it\rho}_{1})=0.48$. The liquid-filled tank is attached to a test sled that is accelerated downwards along a vertical rail system using a system of weights and pulleys producing approximately $1g$ net acceleration. The tank is backlit and images are digitally recorded using a high-speed video camera. The experiments are either initiated with forced initial perturbations or are left unforced. The forced experiments have an initial perturbation imposed by vertically oscillating the liquid-filled tank to produce Faraday waves at the interface. The unforced experiments rely on random interfacial fluctuations, resulting from background noise, to seed the instability. The main focus of this study is to determine the effects of forced initial perturbations and the effects of miscibility on the growth parameter, ${\it\alpha}$. Measurements of the mixing-layer width, $h$, are acquired, from which ${\it\alpha}$ is determined. It is found that initial perturbations of the form used in this study do not affect measured ${\it\alpha}$ values. However, miscibility is observed to strongly affect ${\it\alpha}$, resulting in a factor of two reduction in its value, a finding not previously observed in past experiments. In addition, all measured ${\it\alpha}$ values are found to be smaller than those obtained in previous experimental studies.

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

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

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

Simulation of the Tilted Rig Experiment

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

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

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