Temporal properties of secondary drop breakup in the multimode breakup regime

Secondary drop breakup due to shock wave disturbances was studied for the m ultimode breakup regime, emphasizing the temporal evolution of breakup for shock wave disturbances. Measurements were carried out in a shock tube usin g pulsed shadowgraphy and holography to observe the mechanism and outcome o f breakup. Test conditions involved water and ethanol drops, liquid/gas den sity ratios greater than 500, Ohnesorge numbers less than 0.1 and Weber num bers of 15-150. The evolution of properties in the multimode breakup regime with increasing Weber number begins at the end of the bag breakup regime w ith the appearance of a plume drop at the apex of the bag at a Weber number of roughly 15, continues in a bag/plume breakup regime which involves the presence of both bag-like structures and plume drops and transitions when b ags are no longer present at a Weber number of roughly 40, and ends with a plume/shear breakup regime which involves development of plume-like structu res that progressively evolve into a parent drop and ligament system as the shear breakup regime is approached at a Weber number of roughly 80. Measur ements over the test range provide breakup times, drop deformation properti es and drag coefficients before the onset of breakup, distributions of drop liquid and resulting drop sizes for various breakup structures, drop veloc ities after breakup, and liquid removal rates during breakup; all these pro perties are provided as a function of Weber number in the multimode breakup regime. (C) 2001 Elsevier Science Ltd. All rights reserved.