An Investigation of the Influence of Initial Conditions on Rayleigh-Taylor Mixing

Abstract

Experiments and direct numerical simulations (DNS) have been performed to examine the e¤ects of initial conditions on the dynamics of a Rayleigh-Taylor unstable mixing layer. Experiments were performed on a water channel facility to measure the interfacial and velocity perturbations initially present at the two-‡uid interface in a small Atwood number mixing layer. The experimental measurements have been parameterized for use in numerical simulations of the experiment. Two-and threedimensional DNS of the experiment have been performed using the parameterized initial conditions. It is shown that simulations implemented with initial velocity and density perturbations, rather than density perturbations alone, are required to match experimentally-measured statistics and spectra. Data acquired from both the experiment and numerical simulations are used to examine the role of initial conditions on the evolution of integral-scale, turbulence, and mixing statistics. Early-time turbulence and mixing statistics are shown to be strongly-dependent upon the early-time transition of the initial perturbation from a weakly-nonlinear to a strongly-nonlinear ‡ow.

Experimental characterization of initial conditions and spatio-temporal evolution of a small-Atwood-number Rayleigh–Taylor mixing layer

“…In the present work, a minimum value of θ ≈ 0.4 was measured and occurs at the same time τ ≈ 0.4 as in Ramaprabhu & Andrews (2004a), but is lower than their reported value θ = 0.68. The difference between the measured values of θ reported here and by Ramaprabhu & Andrews (2004a) is attributed to the difference in the size of the thermocouple probes and to the noise elimination techniques used in the present work (Mueschke 2004;Mueschke & Andrews 2006). Ristorcelli & Clark (2004) report a similar two-stage behaviour of θ(z = 0, τ ); however, the exact time of transition and the minimum value of θ differ.…”

“…The current measurements exhibit a 5% difference between the mean advection velocity (U m = 5.15 cm/s) and the minimum velocity within the wake (u min = 4.9 cm/s) at x = 1.0 cm downstream. This reduction in the velocity deficit behind the splitter plate is attributed to the existence of smaller boundary layers at the knife-edge of the splitter plate, which are a result of modifications to the upstream screen meshes (Mueschke 2004). In addition to the velocity deficit, two thin layers of higher velocity (u ≈ 5.4 cm/s) fluid exist just above and below the wake of the splitter plate and are likely due to the velocity profile induced by the series of upstream screen meshes.…”

Statistically steady measurements of Rayleigh-Taylor mixing in a gas channel

“…Over the last 12 years, various diagnostics have been established at the water channel facility to extensively study R-T mixing. Diagnostics involve digital image analysis (Snider 1994;Snider & Andrews 1994;Snider & Andrews 1996), particle image velocimetry (Mueschke 2004;Ramaprabhu & Andrews 2003;2004;Wilson 2002) and high resolution thermocouple measurements (Mueschke 2004;Mueschke & Andrews 2005;Ramaprabhu & Andrews 2003;2004;Wilson 2002;Wilson & Andrews 2002). Since the water channel uses hot and cold water, the Atwood number that can be studied is small (AB t B ~ 10P -4…”