Dynamics of drop deformation and formation during secondary breakup in the bag breakup regime

Secondary drop breakup in the bag breakup regime was studied experimentally. The properties of the parent drop, as well as the properties of drops formed by secondary breakup, were measured as a function of time for shockwave-initiated disturbances in air at normal temperature and pressure. The test liquids included water, ethyl alcohol, and various glycerol mixtures to yield Weber numbers of 13-20, liquid/gas density ratios of 633-893, Ohnesorge numbers of 0.0043-0.0427, and Reynolds numbers of 1550-2150. Measurements involved single- and double-pulse shadowgraphy and holography to yield the structure, size, and velocity of the parent drop, and the sizes and velocities of drops produced by secondary breakup, as a function of time during the breakup process. The parent drop undergoes significant deformation and lateral growth during breakup, forming a thin bag having a basal ring that is characteristic of the bag breakup regime. The ring contains roughly 60 percent of the initial drop volume and eventually yields drops having mean diameters of roughly 30 percent of the initial drop diameter by a Rayleigh breakup process; drop size variations of these ring drops increase with increasing Weber numbers due to the formation of large 'node' drops that are characteristic of the onset of the multimode breakup regime. (Author)