On the breakup mechanisms of air-assisted drops in a high speed air

Abstract

An experimental study was performed to investigate break-up mechanisms of liquid drops injected into a transverse high velocity air jet. The range of conditions included the three drop breakup regimes previously referred to as bag, shear or boundary layer stripping, and ‘catastrophic’ breakup regimes. The results show that the break-up mechanism consists of a series of processes in which dynamic pressure effects deform the drop into a thin liquid sheet. The flattened drop subsequently breaks up into small droplets. At high relative velocity, in the ‘catastrophic’ breakup regime, drops are flattened and fragmented by relatively large wavelength waves whose wavelengths and growth rates are consistent with estimates from Rayleigh-Taylor instability theory. The minute drops that are also produced at this high relative velocity appear to originate from short wave length of Kelvin-Helmholtz waves growing on the larger liquid fragments.