Linear capillary instability of compound jets

Abstract

The capillary instability of compound jets has been studied using a linear model derived from the two-dimensional equations of motion. The flow was considered as a superposition of steady-state plug flow and travelling waves of small amplitude. The eigenvalue problem, obtained via the disturbance-phase velocity, was solved numerically and the analysis applied to compound jets of liquids with different surface tensions, densities and viscosities. The influence of the outer secondary-fluid layer on the compound jet instability was analysed. Three different break-up regimes were established and the distance to the first break-up point was predicted. The necessary qualitative conditions for manifesting a specific break-up regime were identified, and the numerical results compared, whenever possible, with the experimental data available.