Direct numerical simulations of elongated bubbles in the presence of surfactants*

The effect of surfactants on elongated bubbles in creeping flows (Re<<1) has been studied in the past both analytically and numerically (Ratulowski and Chang, 1990; Park, 1992; Stebe and Barthes-Biesel, 1995; Olgac and Muradoglu, 2013). These studies showed that surfactants tend to accumulate at the bubble tail and modify its shape. At much higher Reynolds numbers (Re>>1), studies for surfactants-free configurations show that the tail of the elongated bubble exhibits undulations along the liquid film (Magnini, 2017). The present work investigates the impact of surfactants on tail undulations. Numerical investigations are carried out using 3D DNS simulations of elongated bubbles in pipes in the presence of soluble and insoluble surfactants, using the hybrid front-tracking code BLUE (Shin et al., J. Comp. Phys. 2018).