Statistics and dynamics of a liquid jet under fragmentation by a gas jet

Abstract

The breakup of a liquid jet by a surrounding gas jet is studied in a coaxial configuration using high-speed back-lit imaging. This work focuses on the time dynamics and the statistics of the length of the liquid jet. The inlet velocities are varied for both fluids to obtain a wide range of gas and liquid Reynolds numbers and equivalently a wide range of gas-to-liquid dynamic pressure ratio M and Weber number. The variety of scales exhibited throughout this range, exploring two breakup regimes, is covered by adapting the spatial and temporal resolutions as well as the field of view of the imaging system. An in-depth study of the distributions of the length of the liquid jet is presented, with the associated scalings for the evolution of the first three statistical moments with the relevant dimensionless parameters, fully describing the statistics through a unique function. The first two moments of the distributions are shown to be power laws of M and their ratio is observed to be constant. The temporal dynamics are studied using autocorrelation functions of the length of the liquid jet. The correlation times are shown to be controlled by the gas jet, with a secondary influence of the liquid Reynolds number through a change of behavior that appears to be related to the onset of liquid turbulence. In addition, a transition between two regimes highlighted by a change of shape of both the probability density and autocorrelation functions of the liquid core length is introduced and its link to the turbulence characteristics of the gas jet and the underlying breakup mechanisms is discussed.