Nonlinear evolution of an isolated disturbance at two-phase flow interface

The nonlinear evolution of an isolated, finite-amplitude wave at the interface between two immiscible fluids of different density is simulated by means of a discrete vortex method. In contrast to a periodic disturbance, that evolves into the familiar train of Kelvin-Helmholtz (KH) linear rolls, the single-wave scenario possess unique features that are not yet well understood. The aim of the present contribution is to provide an in-depth description of the nonlinear wave evolution, and to highlight the different features that distinguish the nonlinear case from the classical KH model. The two-phase interface is represented by a discrete vortex sheet, whose dynamics is simulated by a point vortex method that accounts for density stratification, surface tension and gravity. It is found that the different topology of streamlines occurring in the two cases determine a nonlinear wave speed that is different from the one predicted by classical KH theory. The instability onset threshold, as well as other flowfield properties also change accordingly.