Solutions of the buoyancy-drag equation with a time-dependent acceleration

Abstract

We perform the analytic study of the buoyancy-drag equation with a time-dependent acceleration γ(t) by two methods. We first determine its equivalence class under the point transformations of Roger Liouville, and thus for some values of γ(t) define a time-dependent Hamiltonian from which the buoyancy-drag equation can be derived. We then determine the Lie point symmetries of the buoyancy-drag equation, which only exist for values of γ(t) including the previous ones, plus additional classes of accelerations for which the equation is reducible to an Abel equation. This allows us to exhibit two régimes for the asymptotic (large time t) solution of the buoyancy-drag equation. It is shown that they describe a mixing zone driven by the Rayleigh–Taylor instability and the Richtmyer–Meshkov instability, respectively.

Keywords:

• Buoyancy-drag equation
• Lie point symmetries
• Abel equation

2010 Mathematics Subject Classification:

• 22E99
• 34Mxx (see also 30Dxx, 32G34)
• 76Fxx (see also 37-XX, 60Gxx, 60Jxx)