Temporal properties of drop breakup in the shear breakup regime

The temporal properties of drop breakup in the shear breakup regime were studied using pulsed shadowgraphy and holography for shock wave disturbances in air at normal temperature and pressure. Test conditions included Weber numbers of 125-375, Ohnesorge numbers of 0.003-0.040, liquid/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 exhibited transient and quasi-steady regimes as a function of time. The velocity distribution functions of drops produced by breakup were uniform, with mean drop velocities somewhat larger than the velocity of the parent drop and rms drop velocity fluctuations of 30-40% of the mean streamwise velocity of the gas relative to the parent drop, at each instant of time. The rate of liquid removal from the parent drop was correlated reasonably well by a clipped Gaussian function. The measurements showed that shear breakup is not a localized event; instead, it extends over streamwise distances of 0-100 initial drop diameters, which suggests that it should be treated as a rate process, rather than by jump conditions, in some instances. (C) 1997 Elsevier Science Ltd.