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Graduate Aeronautical Laboratories
Caltech
Abstract-
Direct Numerical Simulations (DNS) of three-dimensional, Rayleigh-Taylor
instability (RTI) between two incompressible, miscible fluids, with a 3:1
density ratio will be discussed. Solutions are obtained for the
Navier-Stokes equations, augmented by a species transport-diffusion
equation, with various initial perturbations. The DNS achieved outer-scale
Reynolds numbers, based on mixing-zone height and its rate of growth, in the
range of 3000 to 3700. Initial growth is found to be diffusive and
independent of the initial perturbations. Following the diffusive-growth
stage, growth rates are found to depend on the initial perturbations,
through the end of the simulations. Mixing is found to be even more
sensitive to initial conditions than growth rates. Taylor microscales and
Reynolds numbers are anisotropic throughout the simulations. Improved
collapse of many statistics is achieved if the height of the mixing zone,
rather than time, is used as the scaling or progress variable. Mixing has
dynamical consequences for this flow, since it is driven by the action of
the imposed acceleration field on local density differences.
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