Rayleigh-Taylor instability in complex stratifications

Rayleigh-Taylor instability has received considerable attention over recent years due to its fundamental rôle in the mixing processes of many stratified flows, and due to the close relationship between it and Richtmyer-Meshkov instability. Recent advances in numerical models and improved experimental diag-nostics have shown a convergence in our ability to model the development of the instability, despite there being a number of significant areas where our understanding is still limited. However, to date both nu-merics and experiments have been largely confined to the simplest possible case: two layers of different but uniform density, and quiescent (or as near as may be achieved experimentally) initial conditions. This paper presents results from an experimental study of flows one level greater in complexity. In particular, we investigate the effect of introducing a third layer to the problem. The densities of the three layers, ρ1, ρ2 and ρ3 (from top to bottom) are chosen so that one interface is unstable with ρ1> ρ2, and the second interface stable with ρ2 < ρ3. To understand the development of the flow also requires knowledge of the relationship between ρ1 and ρ3 and the relative depths of the layers on either side of the unstable interface. We present results for the globally stable ρ1 < ρ3, neutral ρ1 = ρ3 and unstable ρ1> ρ3 cases. 2