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

Abstract

A novel gas channel experiment was constructed to study the development of high Atwood number Rayleigh-Taylor mixing. Two gas streams, one containing air and the other containing helium-air mixture, flow parallel to each other separated by a thin splitter plate. The streams meet at the end of a splitter plate leading to the formation of an unstable interface and of buoyancy driven mixing. This buoyancy driven mixing experiment allows for long data collection times, short transients and was statistically steady. The facility was designed to be capable of large Atwood number studies of AB t B ~ 0.75. We describe work to measure the self similar evolution of mixing at density differences corresponding to 0.035 < AB t B < 0.25. Diagnostics include a constant temperature hot-wire anemometer, and high resolution digital image analysis. The hot-wire probe gives velocity, density and velocity-density statistics of the mixing layer. Two different multi-position single-wire techniques were used to measure the velocity fluctuations in three mutually perpendicular directions. Analysis of the measured data was used to explain the mixing as it develops to a self-similar regime in this flow. These measurements are to our iv knowledge, the first use of hot-wire anemometry in the Rayleigh-Taylor community.Since the measurement involved extensive calibration of the probes in a binary gas mixture of air and helium, a new convective heat transfer correlation was formulated to account for variable-density low Reynolds number flows past a heated cylinder. In addition to the hot-wire measurements, a digital image analysis procedure was used to characterize various properties of the flow and also to validate the hot-wire measurements. A test of statistical convergence was performed and the study revealed that the statistical convergence was a direct consequence of the number of different large three-dimensional structures that were averaged over the duration of the run.

Nonideal Rayleigh–Taylor mixing

“…We found excellent agreement between simulations and a miscible experiment (28) and with several immiscible experiments (29,30). See Fig.…”

Incompressible Rayleigh–Taylor Turbulence

“…The picture which emerges is that the measurement of ↵ from the fit of h(t) with t 2 is sensitive to the transient behavior which depends on the initial perturbation of the interface. It has been found that, in general, experimental measurements give a value of ↵ in the range 0.05 0.07 (Snider & Andrews 1994;Read 1984;Dimonte & Schneider 1996;Linden et al 1994;Schneider et al 1998;Banerjee & Andrews 2006) while numerical simulations report lower values around 0.03 (Cabot & Cook 2006;Dimonte et al 2004;Young et al 2001;Youngs 1991). One possible origin of this di↵erence is due to the presence of long wavelength perturbations in the experiments, while numerical simulations are usually perturbed at small scales.…”

“…3 ) while a more recent setup developed by Banerjee & Andrews (2006) is capable to reach A ' 1. Another, and promising technique developed by Huang et al (2007) makes use of a strong magnetic field gradient to stabilize a paramagnetic (heavy) fluid over a diamagnetic (light) one.…”

Small Atwood number Rayleigh–Taylor experiments

“…Although most earlier high Atwood number R-T experiments were with immiscible fluids, considerable effort now appears to be focused on miscible systems. In addition to the gas tunnel results noted previously (Banerjee & Andrews 2006), preliminary experiments using a variation on the RR (Roberts & Jacobs 2008), and high-pressure gas systems (Kucherenko et al 2003), along with novel approaches such as magnetorheological fluids (White et al 2004), are showing considerable promise, although further progress on the associated diagnostics is necessary to provide the much-needed measurements in this miscible regime.…”

“…brine/water with Sc approximately 700, and hot/cold water with Pr approximately 7. Furthermore, a new gas tunnel experiment at Texas A&M University has been developed for high Atwood number R-T studies (Banerjee & Andrews 2006). …”