The properties of drop deformation and secondary breakup were observed for shock wave initiated disturbances in air at normal temperature and pressure. Test liquids included water, glycerol solutions, n-heptane, ethyl alcohol and mercury to yield Weber numbers (We) of 0.5-1000, Ohnesorge numbers (Oh) of 0.0006-4, liqnid/gas density ratios of 580-12,000 and Reynolds numbers (Re) of 300-16,000. Measurements included pulsed shadowgraphy and holography to find drop deformation properties prior to breakup, as well as drop size distributions after breakup. Drop deformation and breakup regimes were identified in terms of We and Oh: regimes at low Oh include no deformation, nonoseillatory deformation, oscillatory deformation, bag breakup, multimode breakup and shear breakup as We is increased. However, most of these regimes occur at higher We when Oh values are increased, with no breakup observed for Oh > 4 over the present test range. Unified temporal sealing 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. The drop size distribution after breakup satisfied Simmons' universal root normal distribution function for the bag and multimode breakup regimes and could be characterized by the Sauter mean diameter (SMD) alone. Drop sizes after shear breakup, however, did not satisfy this distribution function due to the distorting effect of the core or drop-generating drop. Nevertheless, the SMD after secondary breakup could be correlated in terms of a characteristic liquid boundary layer thickness for all breakup regimes, similar to recent results for nonturbulent primary breakup. Drop properties after secondary breakup suggest that both reduced drop sizes and reduced relative velocities play a role in ending the secondary breakup process.

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Al~traet-Recent advances concerning analysis of sprays and drop/turbulence interactions are reviewed. Consideration is given to dilute sprays and related dilute dispersed flows, which contain well-defined dispersed-phase elements (e.g. spherical drops) and have dispersed-phase volume fractions less than 1%; and to the near-injector, dense spray region, having irregularly-shaped liquid elements and relatively-high liquid fractions. Early analysis of dilute sprays and other dispersed flows assumed either locally-homogeneous flow (LHF), implying infinitely-fast interphase transport rates, or deterministic separated flow (DSF) where finite interphase transport rates are considered, but interactions between dispersed-phase elements and turbulence are ignored. These limits are useful in some instances; however, recent evidence shows that both methods are deficient for quantitative estimates of the structure of most practical dispersed flows, including sprays. As a result, stochastic separated flow (SSF) methods have been developed, which treat both finite interphase transport rates and dispersed phase (drop)/turbulence interactions using random-walk computations for the dispersed phase. Evaluation of SSF methods for particle-laden jets; nonevaporating, evaporating and combusting sprays; and noncondensing and condensing bubbly jets has been encouraging, suggesting capabilities of current SSF methods to treat a variety of interphase processes. However, current methods are relatively ad hoc and many fundamental problems must still be resolved for dilute flows, e.g. effects of anisotropic turbulence, modification of continuous-phase turbulence properties by the dispersed phase (turbulence modulation), effects of turbulence on interphase transport rates, and drop shattering, among others. Dense sprays have received less attention and are poorly understood due to substantial theoretical and experimental difficulties, e.g. the idealization of spherical drops is not realistic, effects of liquid breakup and collisions are difficult to describe, spatial resolution is limited and the flow is opaque to optical diagnostics which have been helpful for studies of dilute sprays. Limited progress thus far, however, suggests that LHF analysis may provide a useful first-approximation of the structure and mixing properties of dense sprays near pressure-atomizing injectors. Since dense-spray processes fix initial conditions needed to rationally analyze dilute sprays, more research is this area is clearly warranted. CONTENTS Nomenclature 294 Yuu et al. 25 : round 0.0008~0.004t 11,000-56,000 Air particle-laden jet McComb and Salih 2~' 27 : Small* 5,000-15,000 Air round particle-laden jet Laats and Frishman28'29: 0.3-1.4' 66,000-137,000 Air round particle-laden jet Levy and Lockwood3°: 1.14 3.50* 20,000 Air round particle-laden jet Shuen et a/.31: