Surface tension effects on two-dimensional two-phase Kelvin–Helmholtz instabilities

The two-dimensional Kelvin–Helmholtz instability is studied using a lattice Boltzmann multi-phase model in the nearly incompressible limit. This study focuses on the effects of surface tension on the evolution of vortex pairing in a two-dimensional mixing layer. Several types of interface pinch-off are observed and the corresponding mechanisms are discussed. The contribution of surface tension to the flow kinetic energy is mainly negative. Part of this kinetic energy can be transformed to potential energy stored in the surface tension. The contribution of surface tension to the flow enstrophy is positive and small vortices are generated near interfaces. Broken interfaces and small vortices near interfaces dominate the late stage of flow fields with strong surface tension.