Transient behavior of liquid jets injected normal to a high-velocitygas stream

Abstract

The transient effects of the breakup and atomization of liquid jets in a crossflow on the size of droplets within the plume were experimentally determined. Water and water/methanol mixtures were injected normal to an air stream at Mach numbers 0.48 and 3, at ambient temperature and at stagnation pressures of 1.4 and 4.3 a tin, and at liquid-to-gas momentum flux ratios from 4-12. Droplet size distributions at sampling rates of up to 9 kHz were obtained using a Fraunhofer diffraction technique. The transients in the liquid mass flow rates were inferred from measurements of the extinction of a laser beam passing through the aerosol. The droplet sizes were found to fluctuate with frequencies of the order of 1-15 kHz. The fluctuations were characterized by a sudden and relatively brief increase in the mean diameter of the droplets caused by the passage of fractured clumps. Also evident was the very small size of the droplets that had been sheared off the windward surfaces of the jet. The jet fracture frequency was related to the frequency of waves propagating along the initial jet column. The axial column waves are postulated to have been caused by jet perturbations created by vortices in the air flow around the jet column.