TEMPORAL PROPERTIES OF DROP BREAKUP IN THE SHEAR BREAKUP REGIME

The temporal properties of drop breakup in the shear breakup regime we re studied using pulsed shadowgraphy and holography for shock wave dis turbances in air at normal temperature and pressure. Test conditions i ncluded Weber numbers of 125-375, Ohnesorge numbers of 0.003-0.040, li quid/gas density ratios of 670-990 and Reynolds numbers of 3000-12000. The size distributions of drops produced by breakup satisfied Simmons ' universal root normal distribution function at each instant of time, with Sauter mean diameters independent of surface tension that exhibi ted transient and quasi-steady regimes as a function of time. The velo city distribution functions of drops produced by breakup were uniform, with mean drop velocities somewhat larger than the velocity of the pa rent drop and rms drop velocity fluctuations of 30-40% of the mean str eamwise velocity of the gas relative to the parent drop, at each insta nt of time. The rate of liquid removal from the parent drop was correl ated reasonably well by a clipped Gaussian function. The measurements showed that shear breakup is not a localized event; instead, it extend s over streamwise distances of 0-100 initial drop diameters, which sug gests that it should be treated as a rate process, rather than by jump conditions, in some instances. (C) 1997 Elsevier Science Ltd.