Summary: | We study the effect of insoluble surfactants on the spatio-temporal evolution of turbulent jets. We use three-dimensional numerical simulations and employ an interfacetracking/level-set method that accounts for surfactant-induced Marangoni stresses. The
present study builds on our previous work (Constante-Amores et al., 2021, J. Fluid Mech.,
922, 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 surfactantinduced 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 surfactant-induced Marangoni stresses.
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