  In this paper, we present the results of a numerical study of air-water
turbulent bubbly flow in a periodic vertical square duct. The study is
conducted using a novel numerical technique which leverages Volume of Fluid
method for interface capturing and Sharp Surface Force method for accurate
representation of the surface tension forces. A three-dimensional geometry
construction method is employed during solution of interface equation which
gives absolute conservation of mass and sharp interface between gas and liquid
phases. The entire algorithm has been implemented on a data parallel mode on
multiple graphics processing units (GPU) taking advantage of the large number
of available cores.
  We have studied the dynamics of a swarm of spherical bubbles co-flowing with
the upward turbulent flow and compared results with an unladen turbulent flow.
The frictional Reynolds number of the unladen $Re_{\tau}$ is 360, which is
sufficient to sustain a turbulent flow. We observe the turbulence-driven
secondary flows in the mean flow, with complex instantaneous turbulent vortical
structures. The interaction of these secondary flows with the upwards rising
bubbles is very complex and leads to significant changes in the instantaneous
and time-averaged flow field.
  We present the results of mean void fraction distribution, mean velocities,
longitudinal and transverse turbulence intensities along the wall, corner
bisector, and wall bisector. A peak in the void fraction distribution near the
walls is observed representing the migration of bubbles to a preferred section
of the duct. The effects of turbulence-driven secondary flows and instantaneous
large eddies on preferential concentration of the bubbles are discussed. The
dispersed bubbles are seen to break the long elongated turbulent structures
commonly observed in the unladen turbulent flow.
