Stochastic simulation of droplet breakup in turbulence

Mohsen Karimi,Ronnie Andersson

doi:10.1016/j.cej.2019.122502

Abstract

This study investigates single droplet breakup from a theoretical perspective and addresses whether breakup in turbulent flows can be studied using highly-resolved simulations. Transient and three-dimensional turbulent flow simulations are performed to investigate if the apparent stochastic outcome from the droplet breakup can be predicted. For a given turbulent dissipation rate the breakup events were simulated for various detailed turbulence realizations. For this purpose, a well-characterized system widely used for kernel development is utilized to validate the simulations with respect to the key characteristics of stochastic breakup, including droplet deformation time, the number of fragments, and the specific breakup rate. The statistical validations show very good agreement with all the quantitative properties relevant to the breakup dynamics. Necklace breakup is also observed in line with patterns found in experiments. Evidence is found that the rate of energy transfer is positively correlated with higher order fragmentation. This can allow development of more accurate breakup kernels compared to the ones that only relies on the maximum amount of energy transfer. It is concluded that the simulation method provides new data on the stochastic characteristics of breakup. The method also provides a means to extract more details than experimentally possible since the analysis allows better spatial and temporal resolutions, and 3D analysis of energy transfer which provides better accuracy compared to experimental 2D data.

Highlights

Physical understanding of droplet breakup benefits the design and optimization of multiphase processes
The breakup event consists of an initial deformation phase during which the droplets deform, and the interfacial energy increases when the disruptive stresses overcome the cohesive stresses, followed by a second phase during which droplets separate from the deformed mother drop
The dynamics of this stage are specified by the deformation time, def, the time required for the droplet to highly deform before fragmentation occurs

Summary

Introduction

Physical understanding of droplet breakup benefits the design and optimization of multiphase processes. It is important to predict how the size distribution of the dispersed phase evolves, how fast the breakup process occurs, and how many daughter droplets are produced in each breakup (i.e. binary, tertiary, or higher order fragmentation). Information about the dynamics of the breakup process leads to. Mother droplet diameter [m] Fi. Interfacial tension force [kg m s−2] g.

Methods

Results

Conclusion