Explosive breakup of a liquid jet by a swirling coaxial gas jet

The breakup of a round water jet by a swirling coaxial annular air jet, issuing from convergent jet nozzles has been studied experimentally. The intensity of the swirl and the water to air mass flux ratio have been varied over a large range. It was found that the liquid jet is little affected by the swirl when the swirl number, here defined by the ratio of tangential to axial air jet nozzle velocities, is below a critical value (S-cr). Just above this value the liquid jet undergoes an explosive radial expansion and disintegration. A simple model shows that the physically relevant parameters are the gas to liquid momentum flux ratio M and the ratio of the nozzle's diameters. For small momentum flux ratios, S-cr was found to depend on M-(1/2) until an asymptotic constant value is reached at large M. Surface tension has no effect on the breakup when air velocities are large, however, membrane-type breakup is dominant at the lower air velocities when the aerodynamic Weber number is of order 100 or less. (C) 1996 American Institute of Physics.