Turbulent diffusion in tall tubes, Part II: confinement by stratification

Rayleigh-Taylor instability between two initially homogeneous layers has been shown to evolve in a self similar manner in high-aspect-ratio domains, and in Part I, we demonstrated close agreement between experimental measurements and a range of modelling approaches. However, changing the initial conditions such that one layer is linearly stably stratified in density introduces an additional length scale to the problem and breaks the global self-similarity seen in the case of homogeneous layers. Here, in Part II, we explore the development of this modified instability. We again compare experimental measurements with a range of modelling approaches, achieving excellent agreement assuming a one-dimensional nonlinear turbulent diffusion, and demonstrating that implicit large eddy simulations are able to capture the detailed development despite limitations in the manner in which both mass and momentum are redistributed by numerical rather than molecular diffusion.