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An experimental study of primary breakup of turbulent liquids in gadliquid mixing layers is described. The experiments involved mixing layers along large liquid jets (3.6.6.4 and 9.5 mm dia.) injected at various velocities into still air at atmospheric pressure with fully-developed turbulent pipe flow at the jet exit. Liquids studied included water, glycerol (42% glycerin by mass) and n-heptane. Pulsed shadowgraph photography and holography were used to find conditions where turbulent primary breakup was initiated and drop sizes and velocities after primary breakup. Drop sizes after primary breakup satisfied Simmons' universal root normal distribution and can be characterized solely by their SMD. Mass weighted mean streamwise and crosstream drop velocities after primary breakup were comparable to mean streamwise and crossweam rms fluctuating velocities in the liquid, respectively, with effects of mean velocity distributions in the jet passage reflected by somewhat lower streamwise drop velocities near the jet exit. Conditions for the initiation of turbulent primary breakup and the variation of SMD with distance from the jet exit were correlated reasonably well by a phenomenological analyses considering effects of surface tension and liquid turbulence properties alone.

The purpose qf this B&f Communications section is to present important research results of more limited scope than regular articles appearing in Physics of Fluids. Submission oj'material of a peripheral or cursory nature is strongly discouraged. Brief Commrmications cannot exceed three printed pages in length, including space allowedjkr title, j?gures, tables, references, and an abstract limited to about 100 words.

An experimental study of primary breakup of turbulent liquids is described, emphasizing liquid/gas density ratios less than 500 where aerodynamics effects are import;tnt. The experiments involved multiphase mixing layers ;dong round water jets (3.6 and 6.2 mm dia.) injected at viirious velocities into still helium, air and Freon 12 at pressures of I iind 2 aim. with fully-developed turbulent pipe flow zit the jet exit. Pulsed shadowgraph photography and holography were uscd io find conditions at the onset of breakup as well as drop properties as a function of dismce from the jet exit. Two main aerc*lyn:miic effects were observed, as follows: (1) enhanced primary breakup near the onset of breakup, and (2) merged primary and secondary breakup when the Rayleigh breakup times of ligaments formed by turbulent fluctuations were longer t l i m the secondary breakup times of similar sized driips. The predictions of phenomenological theories based on these ideas were in good agreemcm with the me;tsurcmenis.