Effects of viscoelasticity and surfactant on turbulent bubbly channel flows
Abstract: Interface-resolved direct numerical simulations are performed to examine the sole and combined effects of soluble surfactant and viscoelasticity on the structure of mon- and poly-dispersed bubbly turbulent channel flows for the friction Reynolds number in the rage between Reτ=127.3 and Reτ=250. A soluble surfactant and FENE-P viscoelastic models are coupled to the incompressible flow equations. In the clean case, small bubbles move toward the wall due to the inertial lift force, resulting in the formation of wall-layers and a significant reduction in the flow rate while larger bubbles tend to move toward channel center. An addition of strong enough surfactant alters the direction of lateral migration, i.e., the contaminated bubbles move toward the core region and spread out across the channel. For the viscoelastic case, shear-thinning effects and elastic forces promote formation of bubbly wall-layers leading to a strong decrease in the flow rate. Formation of a wall-layer is determined by the interplay of the inertial lift, elastic and Marangoni forces when they coexist.
