Near-limit drop deformation and secondary breakup

Abstract

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.

ARO and AFOSR Contractors Meeting in Chemical Propulsion.

“…SECONDARY BREAKUP. Past experimental studies have found secondary drop breakup regimes and outcomes (Hsiang and Faeth 1992, 1993, have shown that secondary breakup should be treated as a rate process , and have resolved the temporal properties of secondary breakup (Chou et al 1997…”

Water droplet deformation and breakup in the vicinity of the leading edge of an incoming airfoil

“…Droplet breakup due to strong aerodynamics forces have been widely studied over the last half-century, starting with the works of Lane [56], Hinze [36], Wolfe and Andersen [102], or Ranger and Nicholls [77,78], passing through Krezeczkowski [54], Pilch and Erdman [73], O'Rourke and Amsden [67], Wierzba and Takayama [101], Wierzba [100] or Hsiang and Faeth [40,41] up to the more recent works of Han and Tryggvasson [30,31], Luxford et al [24,60,59], Chen [14], Theofanous et al [92,91], Guildenbecher [29] and Theofanous [90].…”

“…Some of previous mentioned works were numerical approaches such as those of Han and Tryggvasson [30,31], and Chen [14] or only theorize [36] while the rest were experimental approaches. Most of the experimental studies have been conducted in shock-tubes ( [77,101,40,41]), or wind tunnels ( [56,24,60,59,100,54,92,91,90]). …”

“…Another set of experiments are those of Hsiang and Faeth published in 1992 [40]. They made experiments in a shock tube with the driven section open to the atmosphere, similar to that of Ranger and Nicholls [77], that provided test times of 17-21ms.…”

“…Ranges of the dimensional parameters were: ρ L /ρ G of 580-12000, We of 0.5-1000, Re of 300-16000 and Oh of 0.0006-4, where Ohnesorge number was limited to less than 0.1 for the experiments leading to the outcome of the breakup. A transitional map We versus Oh for the different breakup regimes was presented in figure 1 in [40], where two additional deformation regimes namely non-oscillatory deformation and oscillatory deformation were added and bag-jet breakup regime was namely multimode. For Oh<0.1, the We transition for each regime was 1.1 for non-oscillatory deformation, 3 for oscillatory deformation, 13 for bag breakup, 35 for multimode breakup, and 80 for shear breakup.…”