Secondary breakup of a drop at moderate Weber numbers

Abstract

We present volume of fluid based numerical simulations of secondary breakup of a drop with high density ratio (approx. 1000) and also perform experiments by injecting monodisperse water droplets in a continuous jet of air and capture the breakup regimes, namely, bag formation, bag-stamen, multibag and shear breakup, observed in the moderate Weber number range (20-120). We observe an interesting transition regime between bag and shear breakup for We = 80, in both simulations as well as experiments, where the formation of multiple lobes, is observed, instead of a single bag, which are connected to each other via thicker rim-like threads that hold them. We show that the transition from bag to shear breakup occurs owing to the rim dynamics which shows retraction under capillary forces at We = 80, whereas the rim is sheared away with flow at We = 120 thus resulting in a backward facing bag. The drop characteristics and timescales obtained in simulations are in good agreement with experiments. The drop size distribution after the breakup shows bimodal nature for the single-bag breakup mode and a unimodal nature following lognormal distribution for higher Weber numbers.

Predicting droplet deformation and breakup for moderate Weber numbers

“…It is apparent, however, that there is scattering of the results which is probably ought to the experimental techniques used and the experimental uncertainties. This is more evident for the We number ranges corresponding to different breakup modes, which is shown in Fig.1 (Jain et al, 2015) the bag-stamen mode includes also the bag/plume mode which are very similar (Cao et al, 2007). It is clear from Fig.1a that for a given We number, one has to consider also other parameters and cannot be certain for the breakup outcome.…”

“…care is usually taken in order to minimize the boundary layer of the free jet and obtain A C C E P T E D M A N U S C R I P T 5 a more uniform gas velocity; see selectively (Krzeczkowski, 1980), (Liu and Reitz, 1997), (Lee and Reitz, 2000), (Cao et al, 2007), (Opfer et al, 2012;Opfer et al, 2014), (Flock et al, 2012), (Zhao et al, 2010;Zhao et al, 2013), (Guildenbecher and Sojka, 2011), (Jain et al, 2015) among others. Details for these techniques can be found in (Guildenbecher et al, 2009) among others.…”

“…They usually examine low density ratios in order to achieve smaller breakup timescale η br ; otherwise a longer physical time has to be simulated as also an even more finer mesh would be required (Jalaal and Mehravaran, 2014). Among them, the 3D VOF simulations obtained with the Gerris code (Jain et al, 2015;Jalaal and Mehravaran, 2014;Khare and Yang, 2013) and the…”

“…The grid used is dense in the order of 100-200 cells per radius (cpR); thus the underlying physics behind droplet breakup could be revealed. On the other hand, the physical parameters selected (e.g the density and viscosity ratio) do not allow for direct comparison with experimental results and thus they were qualitatively validated; the work of (Jain et al, 2015) is an exception since their model was successfully validated against their own experimental results.…”

Numerical simulation of the aerobreakup of a water droplet

“…They are, axisymmetric (Han & Tryggvason 2001;Aalburg, Leer & Faeth 2003;Wadhwa, Magi & Abraham 2007;Chang, Deng & Theofanous 2013) approximations. Additionally, fluid density ratios are often assumed to be small, or the fluids are considered to be incompressible (Han & Tryggvason 2001;Aalburg et al 2003;Quan & Schmidt 2006;Jalaal & Mehravaran 2014;Xiao, Dianat & McGuirk 2014;Castrillon Escobar et al 2015;Jain et al 2015). Previous work from the authors (Meng & Colonius 2015) simulated the early stages of two-dimensional aerobreakup, with comparison to the experimental work of Igra & Takayama (2001c).…”