Numerical investigation of the segregation of turbulent emulsions

TL;DR

This study uses direct numerical simulations to analyze how emulsions segregate in decaying turbulence under gravity, focusing on the effects of buoyancy, surface tension, and droplet size distribution.

Contribution

It introduces a detailed numerical investigation of emulsion segregation in decaying turbulence, highlighting the roles of buoyancy, surface tension, and droplet dynamics, along with a new dimensionless energy release number.

Findings

Segregation driven by potential and surface energy minimization.

A dimensionless number correlates energy release with segregation.

Droplet size distribution is affected by surface tension.

Abstract

We study the segregation of emulsions in decaying turbulence using direct numerical simulations (DNS) in combination with the volume of fluid method (VOF). To this end, we generate emulsions in forced homogeneous isotropic turbulence and then turn the forcing off and activate gravitational acceleration. This allows us to study the segregation process in decaying turbulence and under gravity. We consider non-iso-density emulsions, where the dispersed phase is the lighter one. The segregation process is driven by both the minimization of the potential energy achieved by the sinking of the heavier phase, as well as the minimization of the surface energy achieved by coalescence. To study these two processes and their impacts on the segregation progress in detail, we consider different buoyancy forces and surface tension coefficients in our investigation, resulting in five different configurations. The surface tension coefficient also alters the droplet size distribution of the emulsion. Using the three-dimensional simulation results and the monitored data, we analyze the driving mechanisms and their impact on the segregation progress in detail. We propose a dimensionless number that reflects the energy release dominating the segregation. Moreover, we evaluate the time required for the rise of the lighter phase and study correlations with the varied parameters gravitational acceleration and surface tension coefficient.