Numerical study of bubbly flow in a swirl atomizer

Abstract

In this work, we extend our previous research on swirl nozzles by introducing bubbles at the nozzle inlet. A large-scale hollow cone pressure-swirl atomizer is studied using scale-resolving simulations. The present flow conditions target a Reynolds number range of 600 ≤ Re ≤ 910 and gas-to-total volumetric flow rate ratios between 0.07 ≤ β ≤ 0.33 with β = 0 as an experimental and computational reference. The computational setup has relevance to high-viscosity bio-fuel injection processes. The flow rate ratio and bubble diameter sweeps are carried out to study their effect on the inner-nozzle flow and the liquid film characteristics outside the nozzle. The present flow system is shown to pose highly versatile physics, including bubble coalescence, bubble–vortex interaction, and faster liquid film destabilization relative to β = 0 case. The main results are as follows: (1) β is found to have a significant effect on the bimodal bubble volume probability density function inside the swirl chamber. In addition, the total resolved interfacial area of the near-orifice liquid film increases with β. (2) At the representative value of β = 0.2, the exact bubble size at the inlet is observed to have only a minor effect on the swirl chamber flow and liquid film characteristics. (3) The bubble-free (β = 0) and bubbly (β > 0) flows differ in terms of effective gas core diameter, core intermittency features, and spray uniformity. The quantitative analysis implies that bubble inclusion at the inlet affects the global liquid film characteristics with relevance to atomization.