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.
In airblast atomization, the shear between the fast gas and slow liquid streams triggers an interfacial instability. The instability develops into interfacial waves that grow and propagate downstream. The longitudinal and transverse instabilities have a strong influence on the development and breakup of the interfacial waves and also the resulting spray characteristics. While extensive previous studies have been dedicated to the longitudinal instability, less attention has been paid on the traverse development of the interfacial waves. This paper aims at investigating the development of the interfacial waves when turbulent fluctuations are present in the gas inlet, through direct numerical simulation. The mass-momentum consistent volume-of-fluid method has been be used to capture the sharp interface. Turbulent velocity fluctuations are introduced at the gas inlet through a digital filter method. The effect of the inlet gas turbulence intensity on the dominant longitudinal wave frequency and the transverse wave number is characterized by a parametric study.
Atomization of bulk liquids subjected to a supersonic flow is essential to applications such as liquid fuel injection in supersonic propulsion systems. Since high-level details are often difficult to measure in experiments, numerical simulation is an important alternative to shed light on the unclear physics. A detailed numerical simulation (DNS) of liquid atomization in supersonic flows will need to rigorously resolve the shock waves, the interfaces, and the interaction between the two. In the present study, a new simulation framework for compressible multiphase flows is proposed. The geometric volume-of-fluid (VOF) method is employed to advect the sharp interfaces. The convection fluxes of density, momentum, and energy are computed based on the VOF flux, to achieve an important mass-momentum-energy consistence. To suppress spurious oscillations near shocks, numerical diffusion is introduced in single-phase regions away from the interface. The contribution of pressure is incorporated using a projection method, so that the method can be used for flows of all Mach numbers. Different compressible interfacial multiphase flow problems, including the two-phase shocktube, Richtmyer-Meshkov instability (RMI), and shock-drop interaction have been used to test the present method. The linear singlemode RMI with finite Weber and Reynolds numbers are simulated. The simulation results agree very well with the linear stability theory, which clearly affirms the capability of the present method in capturing the viscous and capillary effects on shock-interface interaction.
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