Effect of airflow pressure on the droplet breakup in the shear breakup regime

Abstract

In this paper, the coupled level set volume of fluid and the large eddy simulation methods are adopted to perform three-dimensional simulations of the shear breakup of a water droplet. We investigate the effect of airflow pressure (1–3 atm) on the temporary deformation and breakup characteristics, including the breakup initiations, the cross-stream, and streamwise deformations. In addition, special attention is paid to subsequent sub-droplet size distributions, which are generally ignored by many researchers. The results indicate that different morphologies on the surface of the droplets in the shear breakup regime are in relatively good agreement with the available experimental visualizations. Based on the present method, the physical mechanism for the variations in the wake recirculation with the development of Rayleigh–Taylor instability waves is discussed. Furthermore, higher airflow pressures can significantly increase cross-stream and streamwise deformations. However, the corresponding breakup initiations at high airflow pressures are much earlier than those of parent droplets at low airflow pressures. Specifically, a reduction of 12.17% in the mean sub-droplet sizes is obtained as the airflow pressure increases from 1 atm to 2 atm, while a reduction of less than 0.1% in the mean sub-droplet sizes is obtained at higher airflow pressures from 2 atm to 3 atm. Eventually, there are linear growths of the aggregate superficial area ratios (0.996–28.2) and the mass ratios (3.55%–64.29%) of the sub-droplets to the parent droplet.

Hemline breakup of gel drops subjected to a continuous air flow

“…In SIE, the unstable waves develop near the equator, causing the formation of ligaments and fragments at the edges while the frontal area remains smooth (Kékesi, Amberg & Prahl Wittberg 2016; Zhu et al. 2021). The secondary breakup process of non-Newtonian fluids drop has been investigated in many studies.…”

“…The simulation results indicated that the recirculation zone in the air-flow field significantly influences the pressure distribution on the surface of the droplet, leading to the interior shift of liquid in the droplet and the deformation of the droplet. In SIE, the unstable waves develop near the equator, causing the formation of ligaments and fragments at the edges while the frontal area remains smooth (Kékesi, Amberg & Prahl Wittberg 2016;Zhu et al 2021). The secondary breakup process of non-Newtonian fluids drop has been investigated in many studies.…”

Scale-Resolving Simulation of Shock-Induced Aerobreakup of Water Droplet

“…where ∆ represents the largest dimension of the local FV cell, while C DES stands for a calibration coefficient. This way, the flow regions wherein the grid-based length scale ∆ results in it being sufficiently less than the turbulent length scale (10) are assigned the LES-like mode of the solution. In these regions, the amount of turbulence kinetic energy is locally reduced, which leads to lowering the modeled turbulent eddy-viscosity below the corresponding RANS level.…”

“…Numerical simulations typically attempt to duplicate laboratory experiments, in order to predict the drift, deformation, and successive breakup of parent droplets, e.g., Ref. [10]. Depending on the actual Reynolds and Mach (Ma) numbers, the physics of the process involves a compressible turbulent two-phase flow field that is characterized by a very wide range of spatial and temporal scales.…”

“…In fact, DNS can be performed only by making certain greatly simplifying assumptions, where the flow governing equations are mostly missing physical models for the molecular viscosity and surface tension effects [11]. As an alternative, the large-eddy simulation (LES) approach, where the effect of unresolved small-scale turbulent eddies upon the dynamics of resolved large-scale ones is modeled through subgrid-scale (SGS) modeling, can be utilized [6,10]. However, the computational complexity of LES methods remains very high, since they still require the use of rather fine grids, especially at the interphase region, as well as rather small time integration steps.…”