Direct numerical simulations of turbulent jets: vortex–interface–surfactant interactions

Abstract

We study the effect of insoluble surfactants on the spatio-temporal evolution of turbulent jets. We use three-dimensional numerical simulations and employ an interface-tracking/level-set method that accounts for surfactant-induced Marangoni stresses. The present study builds on our previous work (Constante-Amores et al., J. Fluid Mech., vol. 922, 2021, A6) in which we examined in detail the vortex–surface interaction in the absence of surfactants. Numerical solutions are obtained for a wide range of Weber and elasticity numbers in which vorticity production is generated by surface deformation and surfactant-induced Marangoni stresses. The present work demonstrates, for the first time, the crucial role of Marangoni stresses, brought about by surfactant concentration gradients, in the formation of coherent, hairpin-like vortex structures. These structures have a profound influence on the development of the three-dimensional interfacial dynamics. We also present theoretical expressions for the mechanisms that influence the rate of production of circulation in the presence of surfactants for a general, three-dimensional, two-phase flow, and highlight the dominant contribution of surfactant-induced Marangoni stresses.

Effect of Surfactants on the Splashing Dynamics of Drops Impacting Smooth Substrates

“…In fact, this capillary wave is suppressed for all the surfactant solutions. We theorize that the capillary wave is suppressed by the reduction in surface tension and surface rigidification …”

“…Surfactants are among the most common additives in industry, since their amphiphilic nature causes them to adsorb at free surfaces, enabling surface tension and interfacial properties to be modified . Surfactant dynamics at liquid interfaces are complicated and the focus of many recent studies. − For example, it has been shown that during the jetting and formation of droplets, surfactants remain at the droplet front to then diffuse to the rest of the newly formed surface . It is generally accepted that the surface tension of a freshly formed free surface in a surfactant solution has an initial surface tension close to that of the solvent σ 0 , with surfactants contained in the bulk.…”

Impact of droplets onto surfactant-laden thin liquid films

“…Extensive mesh studies for surface-tension-driven phenomena using the same computational method can be found elsewhere, e.g. Batchvarov et al (2021Batchvarov et al ( , 2020 and Constante-Amores et al (2020, 2021b, 2023.…”

“…Constante-Amores et al. (2021 b , 2020, 2023). Figure 15 displays the temporal evolution of the kinetic energy, , and the conservation of liquid volume for the surfactant-free case ( and ) for different mesh resolutions.…”