Control of spray formation by vibrational excitation of flat-fan and conical liquid sheets

In the present work, we develop a technique for controlling spray formation by vibrational excitation of liquid sheets. The sheets are formed by commercial prefilming pressure atomizers or by a specially designed liquid sheet generator. The excitation controls the drop formation such that narrow drop size spectra are produced. For realizing the technique, a vibrator for moving the atomizers was developed. Investigations with flat-fan atomizers show that, for sufficiently small sheet Weber number, regular-shaped waves on the sheets are formed by the excitation, which results in the formation of regular-shaped ligaments. The latter disintegrate into droplets by the Rayleigh mechanism. The small Weber number keeps the influence of the Kelvin-Helmholtz instability of the sheet (which would disturb the regularity of the drop formation) small. For investigating the controlled breakup of conical sheets, a conical sheet generator was developed, which allows the sheet thickness at the orifice to be varied. Investigations of open water bells show that the excitation may force the formation of regular sprays for this sheet geometry, also. The breakup of the conical sheets is also controlled by preshaping of the sheets due to the nozzle vibrations. For both sheet geometries, our work quantifies the achievable drop sizes and operation windows of the influencing parameters in nondimensional form, inside which the technique can be applied.