Predicting droplet deformation and breakup for moderate Weber numbers

Abstract

1 Highlights  CFD simulation of bi-axial droplet motion in continuous air jet experiment  Comparison against detailed experimental data for droplet breakup  Capturing of droplet breakup regimes for a wide range of Weber numbers  Effect of numerical parameters in predicting droplet breakup  The gas phase recirculation affects the breakup outcome  The pressure interpolation scheme affects the predicted flow field Abstract The present work examines numerically the deformation and breakup of free falling droplets subjected to a continuous cross flow. The model is based on the solution of the Navier-Stokes equations coupled with the Volume of Fluid (VOF) methodology utilized for tracking the droplet-air interface; an adaptive local grid refinement is implemented in order to decrease the required computational cost. Neglecting initially the effect of the vertical droplet motion, a 2D axisymmetric approximation is adopted to shed light on influential numerical parameters. Following that, 3D simulations are ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T 3 performed which include inertial, surface and gravitational forces. The model performance is assessed by comparing the results against published experimental data for the bag breakup and the sheet thinning breakup regimes. Furthermore, a parametric study reveals the model capabilities for a wider range of Weber numbers.It is proved that the model is capable of capturing qualitatively the breakup process, while the numerical parameters that best predict the experimental data are identified.

Aerodynamic breakup of an n -decane droplet in a high temperature gas environment

“…The model has been successfully validated in [33,54,63,67,68] for cases including the motion of a free falling droplet, droplet breakup, droplet evaporation and droplet impact onto a solid substrate.…”

“…at T0=300K for the liquid droplet and at ∞ for the surrounding air; the isothermal runs correspond to a parametric study for the effect of We and Re numbers. Regarding the computational domain and the boundary conditions, these are the same as in Strotos et al [33,61,68], in which a step change of the gas phase velocity is applied around the initially motionless droplet; the 2-D axisymmetric computational domain is moving with the average translational droplet velocity. Upwind the droplet, Dirichlet boundary conditions were applied (i.e.…”

“…More specifically, [7][8][9][10] provided breakup maps in the We-Oh plane, [11][12][13]16] further clarified the boundaries between different breakup regimes, [14,15,20,23,25,30,31] clarified the physical mechanisms behind the breakup regimes, [13,18] examined the size distribution of the child droplets after the parent droplet disintegration, [22] identified experimentally the gas flow structure during droplet breakup, [15,24,26,32] examined the effect of density ratio and [26,27,29,31] examined the droplet drag coefficient. For a detailed presentation of the works referring to droplet breakup, see Strotos et al [33].…”

Numerical investigation of the aerodynamic breakup of diesel droplets under various gas pressures

“…Surface tension forces are included in the momentum equation by using the Continuum Surface Stress (CSS) model of [16]. The CFD model has been validated and used for many applications including the aerodynamic breakup of droplets with high density ratios as described in [17][18][19][20]. The simulations are performed in a 2-D axisymmetric domain with the commercial CFD tool ANSYS FLUENT v16 [21], along with various user defined functions (UDFs) for the implementation of the adaptive local grid refinement [22] and the adaptive time-step for the implicit VOF solver.…”

Transitions of deformation to bag breakup and bag to bag-stamen breakup for droplets subjected to a continuous gas flow

“…Recently, Jain et al [11] studied the droplet breakup in the moderate Weber number range (20-120) with the experimental and numerical (VOF) methods, and a multi-bag breakup mode was observed both in the numerical and experimen- tal results for We = 80. More recently, Strotos et al [39] predicted the droplet deformation and breakup for the moderate Weber numbers with the commercial CFD tool ANSYS FLUENT, and the droplet evaporation process was included [40]. Although the transition mechanism has been explored and analyzed from experimental, theoretical and computational aspects, the underlying physics of the transition mechanism at a wide range of Oh numbers are still far from clearly understood.…”