Ligament Formation and Breakup in Two-Fluid Spray Atomization

Abstract

The present work studies low-viscosity two-fluid atomization experimentally and analytically in order to characterize and predict the formation and breakup of ligaments in the spray. The study is based on experiments conducted using commercially available two-fluid nozzles with water as the liquid. Shadowgraph images were used to visualize and characterize the near-nozzle flow and ligaments while the droplet size distribution was measured in the far-field using a Malvern Spraytec. Our images reveal that two different wave structures contribute to the breakup: surface waves, and bulk waves. These waves eventually result in the formation of structures that breakup with a mechanism similar to droplet breakup, where small droplets are formed from the surface waves and large droplets form from the bulk waves. A recent deformation-rate based droplet breakup model is applied to the surface and bulk wave geometries to predict the formation and breakup of ligaments. These predictions are compared to measurements of the ligament sizes from the shadowgraph images as well as the droplet size distributions with good agreement in the order of magnitude and trends of each mode.