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

Abstract

A novel gas channel experiment is described to study the development of high Atwood number Rayleigh-Taylor mixing. Two gas streams, one containing air and the other containing a 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, has short transients, and is statistically steady. The facility was designed to be capable of large Atwood number studies (At∼0.75). We describe initial validation work to measure the self similar evolution of mixing at density differences (0.035<At<0.1). The purpose of this paper is to describe the new high Atwood number gas channel facility and present validation results for experimental runs at Atwood numbers up to 0.1. Diagnostics include a constant temperature hot wire anemometer, and high resolution digital image analysis. The hot-wire probe gives velocity statistics of the mixing layer. A multiposition single-wire technique was 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. A digital image analysis procedure was used to characterize various properties of the flow and also to validate the hot wire measurements.