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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. 

Understanding the development and breakup of interfacial waves in a two-phase mixing layer between the gas and liquid streams is paramount to atomization. Due to the velocity difference between the two streams, the shear on the interface triggers a longitudinal instability, which develops to interfacial waves that propagate downstream. As the interfacial waves grow spatially, transverse modulations arise, turning the interfacial waves from quasi-two-dimensional to fully three-dimensional. The inlet gas turbulence intensity has a strong impact on the interfacial instability. Therefore, parametric direct numerical simulations are performed in the present study to systematically investigate the effect of the inlet gas turbulence on the formation, development and breakup of the interfacial waves. The open-source multiphase flow solver, PARIS, is used for the simulations and the mass–momentum consistent volume-of-fluid method is used to capture the sharp gas–liquid interfaces. Two computational domain widths are considered and the wide domain will allow a detailed study of the transverse development of the interfacial waves. The dominant frequency and spatial growth rate of the longitudinal instability are found to increase with the inlet gas turbulence intensity. The dominant transverse wavenumber, determined by the Rayleigh–Taylor instability, scales with the longitudinal frequency, so it also increases with the inlet gas turbulence intensity. The holes formed in the liquid sheet are important to the disintegration of the interfacial waves. The hole formation is influenced by the inlet gas turbulence. As a result, the sheet breakup dynamics and the statistics of the droplets formed also change accordingly.