Structure of the near-injector region of nonevaporating pressure-atomized sprays

Abstract

The dense-spray region of pressure-atom ized nonevaporating sprays was studied, emphasizing the properties of the multiphase mixing layer that surrounds the liquid core during atomization breakup. The dispersed-phase properties of a large-scale (9.5-mm injector diameter) water jet injected vertically downward in still air were measured using single- and double-pulse holography for both fully developed and slug flow jet exit conditions. The inner portion of the mixing layer contained large irregularly shaped liquid elements and drops, and the proportion of spherical drops increased and drop sizes decreased with increasing radial distance. For present test conditions, the liquid core and the large liquid elements cause mean liquid volume fractions to be high near the axis; however, the gas-containing region was relatively dilute at each instant. Additionally, the velocities of large drops were generally much larger than small drops and predictions based on the locally homogeneous flow approximation, providing direct evidence of significant separated-flow effects in the flow. Finally, the degree of flow development at the jet exit had a substantial effect on the structure of the mixing layer, with increased turbulence levels increasing the number and size of large irregular liquid elements through distortion of the surface of the liquid core—enhancing rates of removal of liquid from the core.