Instability and atomization of two-layer capillary jets

A theoretical analysis of a two-layer capillary jet consisting of a liquid core and a coaxial layer entrained by a nonmixing fluid flowing into an unperturbed ideal gas is presented. The presence of two families of unstable waves propagating at the velocity of the main flow is demonstrated. These families are predicted by linear theory; and in the case of a compound flow containing a velocity discontinuity, unstable short-wave perturbations connected with the Kelvin-Helmholtz instability are also present. The interaction of these waves at the nonlinear stage leads to (1) the destruction of the compound jet with formation of freely flying droplets of different radii or (2) the destruction of the core with formation of main drops and droplet satellites moving in the entrained-fluid jet.