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Numerical development of Moment of Fluid / Level Set method and Application to liquid jet and sheet atomization

Abstract : With the increase in the passenger air travel, it has become necessary to design fuel efficient engines for long-haul and ultra-long-haul flights. Because of the continuous progress in the supercomputing power and advances in the computational fluid dynamics (CFD) methods, numerical simulations have been sought after as the choice for investigating the physical processes occurring inside the aircraft engines. Of the many processess, atomization of the liquid fuel, i.e., the process by which the injected liquid fuel breaks up into droplets remains imperative to be completely understood. Since atomization processgoverns the size of the fuel droplets produced, it has a direct influence on the evaporation rate, completeness of combustion, and even pollutant formation. However, due to the multiscale, multiphysical, and multiphase aspect of this process, it has become a challenge to numerically simulate it. Most often, the simulations run into under-resolution limitation when capturing the droplets. To mitigate this shortcoming and to make the simulations numerically tractable, this work presents two numerical methods of liquid/gas interface reconstruction to capture the liquid droplets {moment of fluid (MOF) method and hybrid moment of fluid{level set (HyMOFLS) method. These methods are coupled with consistent mass and momentum flux computation as well as ghost fluid method (GFM) for handling discontinuities in density and jump in pressure across the interface. The MOF method uses liquid volume fraction as well as liquid and gas phase centroids for interface reconstruction in each computational cell in the simulations. The advantage in using the phase centroids is that the neighbor cell data are not required in the interface reconstruction process resulting in a uniform treatment of interior and boundary cells in the computational domain. This method improves the liquid/gas interface orientation and reconstruction in the underresolved regions of the domain. The HyMOFLS method combines the MOF method and CLSVOF method such that MOF method is employed to capture under-resolved regions and CLSVOF method for resolved regions of the interface. The switch between the choice of these methods in the computational domain is made according to local mesh spacing and curvature of the interface. This method strikes a good balance between the reconstruction accuracy and modest computational cost requirement compared to MOF method. Hence, it is a natural choice for performing simulations of primary atomization at aircraft engine operating conditions. The HyMOFLS method is employed in to simulate primary atomization of liquid for two injection con_gurations used in aircraft engines under relevant operating conditions. First, a planar pre-filming Airblast atomization configuration is simulated using two gridresolutions and inlet velocity profile to investigate and analyze their effect on the atomization characteristics, i.e., droplet and ligament properties. Results suggest that the simulations are matching satisfactorily with the experiments and are of the same order of magnitude as the experimental data. Next, primary atomization of a turbulent liquid jet in gaseous crossow configuration is simulated under three di_erent (low, moderate,and high) density ratio operating conditions using three different mesh resolutions. The analyses of the results yielded that there is low probability of occurrence of secondary atomization due to aerodynamic forces, the jet bending and penetration decrease with increase in density ratio, and the wavelength of the instability waves formed on the windward side of the liquid jet decreases from low to moderate density ratio and increases from moderate to high density ratio.
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Submitted on : Wednesday, December 23, 2020 - 1:02:03 AM
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Anirudh Asuri Mukundan. Numerical development of Moment of Fluid / Level Set method and Application to liquid jet and sheet atomization. Other. Normandie Université, 2020. English. ⟨NNT : 2020NORMR010⟩. ⟨tel-03086893⟩

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