Near-limit drop deformation and secondary breakup.

An experimental study of the deformation and breakup of liquid drops subjected to both shock wave and steady disturbances is described, emphasizing effects of Weber number, We, and Ohnesorge number, Oh, for various deformation and breakup regimes. Measurements included pulsed shadowgraphy and holography to find drop deformation and drag properties prior to breakup, as well as drop sizes and velocities after breakup. Simplified phenomenological theories were used to help interpret and correlate the measurements. For shock wave disturbances, drop deformation and breakup regimes were identified in terms of We and Oh: regimes at low Oh included no deformation, nonoscillatory deformation, oscillatory deformation, bag breakup, multimode breakup and shear breakup as We is increased. For We $$ 10 while 5% deformation no longer is possible for Oh $>$ 1000. Unified temporal scaling of deformation and breakup processes was observed in terms of a characteristic breakup time that largely was a function of Oh. Prior to breakup, the drag coefficient evolved from the properties of spheres to those of thin disks as drop deformation progressed. Measurements of drop properties after secondary breakup were limited to low Oh conditions. Drop size distributions after breakup satisfied Simmon's universal root normal distribution function in all three breakup regimes, after removing the core drop from the drop population for shear breakup. The Sauter mean diameter after breakup was correlated successfully, independent of the breakup regime, based on consideration of drop stripping in the shear breakup regime. The size and velocity of the core drop after shear breakup were correlated separately, based on the observation that the end of drop stripping corresponded to a constant Eotvos number. The relative velocities of the drop liquid were significantly reduced during secondary breakup, due both to the large drag coefficients caused by drop deformation and the reduced relaxation times of small drops. These effects were correlated successfully, using phenomenological theory. For steady disturbances, significant drop deformation (roughly 5%) began at a We of roughly unity, with the deformation regime ending due to the onset of breakup at We in the range of 10-20. These transitions were relatively unaffected by Oh. Another transition, between dome- and bowl-shaped drops (related to the transition between bag and shear breakup), was correlated mainly in terms of We and Re for present conditions. Drop deformation for steady disturbances was relatively independent of dispersed/continuous phase density ratios but generally was smaller than for shock wave disturbances at comparable conditions due to the absence of overshoot from inertial effects. In contrast, drop drag coefficients, normalized by the drag coefficient of a solid sphere at the same Re, was correlated quite well by the degree of deformation alone.PhDAerospace engineeringApplied SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/129273/2/9423210.pd