Droplets in homogeneous shear turbulence

Abstract

We simulate the flow of two immiscible and incompressible fluids separated by an interface in a homogeneous turbulent shear flow at a shear Reynolds number equal to 15200. The viscosity and density of the two fluids are equal, and various surface tensions and initial droplet diameters are considered in the present study. We show that the two-phase flow reaches a statistically stationary turbulent state sustained by a non-zero mean turbulent production rate due to the presence of the mean shear. Compared to single-phase flow, we find that the resulting steady state conditions exhibit reduced Taylor microscale Reynolds numbers owing to the presence of the dispersed phase, which acts as a sink of turbulent kinetic energy for the carrier fluid. At steady state, the mean power of surface tension is zero and the turbulent production rate is in balance with the turbulent dissipation rate, with their values being larger than in the reference single-phase case. The interface modifies the energy spectrum by introducing energy at small-scales, with the difference from the single-phase case reducing as the Weber number increases. This is caused by both the number of droplets in the domain and the total surface area increasing monotonically with the Weber number. This reflects also in the droplets size distribution which changes with the Weber number, with the peak of the distribution moving to smaller sizes as the Weber number increases. We show that the Hinze estimate for the maximum droplet size, obtained considering breakup in homogeneous isotropic turbulence, provides an excellent estimate notwithstanding the action of significant coalescence and the presence of a mean shear. † Email address for correspondence: merosti@mech.kth.se arXiv:1902.05259v2 [physics.flu-dyn]

Modulation of turbulence by finite-size particles in statistically steady-state homogeneous shear turbulence

“…This effect is amplified by increasing the volume fraction of the solid phase, while the shape effects (spherical versus oblate particles) are observed to be rather negligible. The characteristics of the energy spectrum are similar to the observations of Lucci et al (2010) for solid particles in decaying homogeneous isotropic turbulence and Rosti et al (2019) for droplets in HST; the spectrum modifications have been attributed to the breakup of the large eddies and to the increase of the frequency of the small eddies as a result of the presence of the dispersed phase.…”

Liquid transport in scale space

“…This point should be addressed in future work by considering e.g. homogeneous shear liquid-gas turbulence (Rosti et al 2018(Rosti et al , 2019. Finally, exploring the contribution of the different terms of the scale-by-scale budget emphasizes that the similarity assumption is reasonable for providing a simple closure for the transfer term.…”

“…For providing further insights into the relation of these two terms to anisotropy, one should explore a flow which features a preferential anisotropy direction. In this context, homogeneous shear liquid-gas turbulence as simulated by Rosti et al (2018Rosti et al ( , 2019) can be instructive.…”

A volume-of-fluid method for interface-resolved simulations of phase-changing two-fluid flows

“…This solver allows for several combinations of homogeneous pressure boundary conditions, which is particularly convenient for the computational setups used in the present work. Finally, validations of the interface-capturing procedure in absence of phase change have been reported in [48], and its suitability for simulating complex and turbulent flows demonstrated in [49,50].…”