A large-eddy simulation of a counter-current gas–liquid flow is
performed. At the flat interface where the different fluids meet,
continuity of momentum and momentum fluxes are enforced following
the work of Lombardi et al. [Direct numerical simulation of
near-interface turbulence in coupled gas-liquid flow. Phys Fluids.
1996;8(6):1643–1665]. The increase in vertical vorticity fluctuations
near the interface increases mixing, reducing the thickness of the
inner region of the boundary layer. Such increase reduces shear while
allowing for more frequent backflow motions in the inner region,
being this phenomenon stronger on water. Due to the higher inertia
of water these backflow motions are ultimately responsible for
the streaky structure of shear stresses seen along the interface. The
present study shows that such bimodality in the streamwise velocities
is also seen in the angle distribution of vorticity relative to the
interface, where such angles are linked to the presence of interfaceconnected
and quasi-streamwise vortex cores. Finally, it is shown
that backflow events on the interface shear stresses correlate with
coupled ‘strong’ ejections in the near interface region despite the disparagingly
different near-interface streamwise velocity distributions
on the near interface boundary layers.
