Intermittency in turbulent emulsions

TL;DR

This study explores turbulence in emulsions of two immiscible fluids, revealing that interfaces influence energy flux and intermittency, with turbulence becoming more intermittent at smaller scales and approaching classical turbulence at higher viscosities.

Contribution

First analysis of velocity increments conditioned on phases in turbulent emulsions, showing interface effects on turbulence statistics and intermittency.

Findings

Interfaces reduce skewness of velocity PDFs below the Kolmogorov-Hinze scale.

Multiphase turbulence exhibits higher intermittency than single-phase turbulence.

Increasing viscosity of the dispersed phase makes turbulence statistics approach classical homogeneous isotropic turbulence.

Abstract

We investigate the statistics of turbulence in emulsions of two-immiscible fluids of same density. We compute for the first time velocity increments between points conditioned to be located in the same phase or in different phases and examine their probability density functions (PDF) and the associated structure functions (SF). This enables us to demonstrate that the the presence of the interface reduces the skewness of the PDF at scales below the Kolmogorov-Hinze scale and therefore the magnitude of the energy flux towards the dissipative scales, which is quantified by the third-order SF. The analysis of the higher order SFs shows that multiphase turbulence is more intermittent than single-phase turbulence. In particular, the local scaling exponents of the SFs display a saturation about the Kolmogorov-Hinze scale and below, which indicates the presence of large velocity gradients across the interface. Interestingly, the statistics approach of classic homogeneous isotropic turbulence when significantly increasing the viscosity of the dispersed phase.