Wh. Chou et Gm. Faeth, TEMPORAL PROPERTIES OF SECONDARY DROP BREAKUP IN THE BAG BREAKUP REGIME, International journal of multiphase flow, 24(6), 1998, pp. 889-912
The temporal properties of secondary drop breakup in the bag breakup r
egime were measured as a function of time for shock-wave-initiated dis
turbances in air at normal temperature and pressure. The test liquids
included water, ethyl alcohol and various glycerol mixtures to yield l
iquid/gas density;ratios of 633-893, Weber numbers of 13-20, Ohnesorge
numbers of 0.0043-0.0427 and Reynolds numbers of 1550-2150. Single- a
nd double-pulse shadowgraphy and holography were used to measure the s
tructure, size and velocity of the parent drop, and the sizes and velo
cities of drops produced by secondary breakup. The parent drop undergo
es significant deformation and lateral growth during breakup before fo
rming a thin bag having a basal ring that is characteristic of the bag
breakup regime. The basal ring contains roughly 56% of the initial dr
op volume (mass) and eventually yields drops-having mean diameters of
roughly 30% of the initial drop diameter by a Rayleigh breakup process
; the size variations of drops formed from the basal ring increases wi
th increasing Weber number due to the appearance of large 'node' drops
that are characteristic of the onset of the multimode breakup regime.
Breakup of the bag yields nearly monodisperse drops having diameters
of roughly 4% of the initial drop diameter. The velocity distributions
of the drops formed from breakup of the basal ring and the bag were i
ndividually independent of drop size but varied as a function of time
and differed between the two groups. Many features of these phenomena
were Successfully correlated using phenomenological analyses. Finally,
bag breakup requires considerable time (5-6 characteristic secondary
drop breakup times) and extends over considerable streamwise distances
(50-100 initial drop diameters) by the end of breakup, which,suggests
that bag breakup should be treated as a rate process, rather than by
jump conditions, in some instances. (C) 1998 Elsevier Science Ltd. All
rights reserved.