The effect of bubbles on vortical flows near walls is examined by direct numerical simulations. A simple model problem, consisting of two slightly perturbed counter rotating vortex tubes plus a parabolic pressure driven velocity profiles is used. Initially, the flow is seeded with several bubbles near the wall. As the flow evolves, the bubbles are entrained into the vortices, where they accelerate the breakdown of the vortices. The flow rate and the wall shear is monitored and the result show that the presence of bubbles leads to a slight decrease in drag and thus an increase in flow rate.
Asymptotic modelling and direct numerical simulations of multilayer pressure-driven flows