Polymer drag reduction in surfactant-contaminated turbulent bubbly channel flows

TL;DR

This study uses advanced simulations to explore how surfactants and viscoelasticity influence bubble behavior and drag reduction in turbulent channel flows, revealing that surfactants can restore drag reduction lost due to viscoelastic effects.

Contribution

It provides new insights into the combined effects of surfactants and viscoelasticity on bubbly flow dynamics and drag reduction using detailed interface-resolved simulations.

Findings

Small amounts of Triton X-100 prevent bubble clustering in Newtonian flows.

Surfactants influence bubble-wall layer formation in viscoelastic flows.

Triton X-100 restores 25% drag reduction in viscoelastic bubbly flows.

Abstract

Polymer additives are commonly utilized to manipulate bubbly flows in various applications. Here, we investigate the effects of clean and contaminated bubbles driven upwards (upflow) in Newtonian and viscoelastic turbulent channel flows. Interface-resolved direct numerical simulations are performed to examine sole and combined effects of soluble surfactant and viscoelasticity using an efficient 3D finite-difference/front-tracking method. The incompressible flow equations are solved fully coupled with the FENE-P viscoelastic model and the equations governing interfacial and bulk surfactant concentrations. The latter coupling is accomplished by a non-linear equation of state that relates the surface tension to the surfactant concentration. For Newtonian turbulent bubbly flows, the effects of Triton X-100 and 1-Pentanol surfactant are examined. It is observed that the sorption kinetics highly affect the dynamics of bubbly flow. A minute amount of Triton X-100 is found to be sufficient to prevent the formation of bubble clusters restoring the single-phase behavior while even two orders of magnitude more 1-Pentanol surfactant is not adequate to prevent the formation of layers. For viscoelastic turbulent flows, it is found that the viscoelasticity promotes formation of the bubble-wall layers and thus the polymer drag reduction is completely lost for the surfactant-free bubbly flows, while the addition of small amount of surfactant (Triton X-100) in this system restores the polymer drag reduction resulting in $25\%$ drag reduction for the $Wi=4$ case.