The instability of viscous capillary jets subject to disturbances consisting of two superposed wavenumbers, and for large disturbance amplitudes is investigated. Disturbances composed of the superposition of a fundamental disturbance (first harmonic) with either its second or third harmonic are used. The influence of the wavenumber of the fundamental disturbance on the jet breakup is studied for a disturbance composed of a first harmonic with an initial non-dimensional amplitude of ε1 = 0.01 and a second harmonic with an initial non-dimensional amplitude of ε2 = 0.05. The influence of the initial amplitudes of the first and second harmonics on the jet breakup is studied for two non-dimensional wavenumbers of the fundamental (first harmonic): k = 0.45 and k = 0.7; the second harmonic is unstable in the former and stable in the latter case. The effect of an added third harmonic is studied only for k = 0.45 but for a wide range of initial amplitudes. All cases are studied for an in-phase and a 180° out-of-phase superposition of the two waves. The nonlinear interaction between the two waves results in the formation of a variety of drop sizes and shapes. The breakup times can be controlled within a wide range using this technique.

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