Abstract
Mixing generated by gravitational acceleration and the role of local turbulence measured through multifractal methods is examined in numerical experiments of Rayleigh-Taylor and RichtmyerMeshkov driven front occurring at density interfaces. The global advance of the fronts is compared with laboratory experiments and Nusselt and Sherwood numbers are calculated in both large eddy simulation (LES) and kinematic simulation KS models. In this experimental method, the mixing processes are generated by the evolution of a discrete set of forced turbulent plumes. We describe the corresponding qualitative results and the quantitative conclusions based on measures of the density field and of the height of the fluid layers. We present an experimental analysis to characterize the partial mixing process. The conclusions of this analysis are related to the mixing efficiency and the height of the final mixed layer as functions of the Atwood number, which ranges from 9.8 × 10 −3 to 1.34 × 10 −1 .
Highlights
Numerical results on the advance of a mixing or non-mixing front occurring at a density interface due to gravitational or forced acceleration are analyzed considering the fractal structure of the front; the numerical simulations
The box-counting algorithm, able to detect the self-similar characteristics for different image intensity levels, This technique is used in the Numerical simulations for velocity, vorticity and volume fraction images reflecting a physical aspect that is advected by the RT or RM flows, we can thereby define the fractal dimension D(i) as a function of the intensity i of the relevant variable
Information about the mixing can be extracted from the thickening of the edges due to the phenolphthalein color change in [2], or in the numerical simulations, and this thickness can be analyzed with a digitizer system
Summary
Numerical results on the advance of a mixing or non-mixing front occurring at a density interface due to gravitational or forced acceleration are analyzed considering the fractal structure of the front; the numerical simulations. In almost all practical circumstances, at high Reynolds number, the instabilities form a turbulent front between the two layers, which in principle should become independent of the initial conditions as turbulence develops. The advance of this front is described in [1] [2] when forced by RT and in [3] driven by RM. In the context of determining the influence of structure on mixing ability, multifractal analysis is used to determine the regions of the front which contribute most to molecular mixing Both the global and local Nusselt and Sherwood numbers are calculated
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