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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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Benefits of AMR for Atomization Calculations
Adaptive mesh refinement (AMR) has been introduced as an attractive means of significantly improving computational efficiency for a variety of two-phase flow problems. In the current study, the benefits of AMR are investigated for the case of liquid jet atomization. The evaluation consists of a systematic analysis of results from the interDymFoam (AMR octree) and interFoam (static octree) codes, both of which form part of the family of solvers distributed within the open source OpenFOAM C++ Toolbox. The two-phase flow treatment is based on an algebraic VoF methodology. As a preliminary set of exercises, cases for pure advection, stationary wave dynamics, and Rayleigh-Plateau breakup of a cylindrical liquid element are considered. The results from these exercises confirm the expected trend of higher numerical efficiency in AMR, while still retaining essentially the same level of accuracy as the fixed embedded mesh solutions. However, for the liquid jet atomization, the behavior is a bit more complicated. First, at lower levels of Weber number, we observe a similar trend as the preliminary exercises. At higher Weber numbers, due to a noticeable increase in interfacial area density, substantial inhomogeneities are formed in the underlying grids yielding slower solutions of pressure Poisson equation, thereby potentially offsetting the benefits of this approach. In fact, at much higher Weber numbers, for instance, those pertaining to Diesel injection, the results suggest that a fixed embedded mesh would provide better computational efficiency. However, this conclusion depends on the target lowest level of numerical resolution, Δxmin. The current work shows how the efficiency of AMR suffers from increasing interfacial area density, and how this can be alleviated via a decrease in Δxmin. Various test cases are presented to illustrate this effect.
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- Award ID(s):
- 1703825
- PAR ID:
- 10063167
- Date Published:
- Journal Name:
- ICLASS 2018, 14th Triennial International Conference on Liquid Atomization and Spray Systems
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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