Density and Growth Rate Measurements in a High Atwood Number Rayleigh-Taylor Mixing

Abstract

A novel gas channel experiment is used to study the non-equilibrium development of high Atwood number Rayleigh-Taylor mixing. Two gas streams, one containing air-helium mixture and the other air, 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 initiation of buoyancy driven mixing. This set up is statistically steady and allows for long data collection times. Here, we describe initial measurements to determine the density profile and growth rate along the mix at low density differences (At ~ 0.05). The facility is however designed capable of large Atwood number studies (At ~ 0.75). Diagnostics include high resolution digital image analysis, which is used to determine the density profile across the mix. The growth parameter (α) is also estimated by a “moving window” calculation. The results are then verified with measurements of α made by a Constant temperature (CT) hot-wire probe and with the growth parameter obtained from small Atwood number experiments (At ~ 0.001). However, there were some inherent errors in the density profile measurements because of non-uniformity in the concentration of smoke. To verify that these errors were indeed measurement errors and not as a result of lack of statistical convergence, a detailed statistical convergence test was performed. It showed that convergence was a direct consequence of the number of different large 3D structures that were averaged over the duration of the run.