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Aerobreakup of drops is a fundamental two-phase flow problem that is essential to many spray applications. A parametric numerical study was performed by varying the gas stream velocity, focusing on the regime of moderate Weber numbers, in which the drop deforms to a forward bag. When the bag is unstable, it inflates and disintegrates into small droplets. Detailed numerical simulations were conducted using the volume-of-fluid method on an adaptive octree mesh to investigate the aerobreakup dynamics. Grid-refinement studies show that converged three-dimensional simulation results for drop deformation and bag formation are achieved by the refinement level equivalent to 512 cells across the initial drop diameter. To resolve the thin liquid sheet when the bag inflates, the mesh is refined further to 2048 cells across the initial drop diameter. The simulation results for the drop length and radius were validated against previous experiments, and good agreement was achieved. The high-resolution results of drop morphological evolution were used to identify the different phases in the aerobreakup process, and to characterize the distinct flow features and dominant mechanisms in each phase. In the early time, the drop deformation and velocity are independent of the Weber number, and a new internal-flow deformation model, which respects this asymptotic limit, has been developed. The pressure and velocity fields around the drop were shown to better understand the internal flow and interfacial instability that dictate the drop deformation. Finally, the impact of drop deformation on the drop dynamics was discussed.
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Effect of Reynolds number on aerobreakup of small liquid drops
Aerobreakup of liquid drops are important to many droplet applications, such as fuel injection. When a liquid drop is subjected to a gas stream of high velocity, the drop can deform and break into small droplets. The drop aerobreakup is controlled by multiple dimensionless parameters. The Weber number (We) has been commonly used to characterize the different breakup regimes. While the effects of Weber and Ohnesorge numbers on the aerobreakup of a drop in unbounded domain have been extensively studied, the effect of the Reynolds number (Re) based on gas properties are less understood and will be investigated by 2D axis-symmetric and 3D detailed numerical simulations in the present paper. Attention will be focused on the moderate We regime, where the drop mostly breaks in the bag mode. In many previous studies for millimeter drops, Re is too large to be relevant. However, for applications where drops are small and the relative velocity is high, Re can be quite small when the drop breaks. Parametric simulations of Re and We are performed to systematically investigate the effect of Re on the drop aerobreakup dynamics. The simulations are performed using the Basilisk solver, where the mass-momentum consistent VOF method is used to capture the interfacial dynamics on an adaptive mesh. The reduced Re is found to induce significant changes in the drop acceleration, deformation, bag morphology, and the bag breakup dynamics, which in turn lead to significant variation in the size and spatial distributions of the children droplets formed.
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- Award ID(s):
- 1853193
- PAR ID:
- 10300475
- Date Published:
- Journal Name:
- ICLASS 2021, 15th Triennial International Conference on Liquid Atomization and Spray Systems, Edinburgh, UK
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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