Direct Numerical Simulation of Microbubble Dispersion in Vertical Turbulent Channel Flow

Abstract

AbstractIn this work, direct numerical simulation of turbulence is coupled to lagrangian tracking to study the behavior of 220 μm bubbles in a vertical turbulent channel flow. Both one-way and two-way coupling approaches and both upward and downward flows are considered. For each simulation, the same external imposed pressure gradient is considered. In one-way simulations, this leads to a shear Reynolds number of Re = 150. In the coupled cases, the presence of bubbles increase/decrease the driving pressure gradient, respectively in upward/downward flow, thus yielding to an increase/decrease of the wall shear stress and of the shear Reynold number. For the considered bubble average volume fraction (α = 104 ), the corresponding shear Reynolds number are about Re τ,2U= 174 for the upflow case and Re τ,2D= 121 for the downflow case. Statistics of the fluid and of the bubble phase are presented. The interactions between bubble and the near-wall turbulence structures is also investigated and a preferential bubble segregation in high-speed/low-speed zones is observed for the upflow/downflow cases respectively. An attempt to describe the transfer rate between the gas and the liquid will be included with some preliminary results.KeywordsWall Shear StressDirect Numerical SimulationVoid FractionLift ForceBubble BehaviorThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.