This paper presents the results from a one-way coupled, Euler-Lagrangian, direct numerical simulation of bubbles injected into a turbulent boundary layer. The Reynolds number of the turbulent boundary layer varies from 420<Reθ<1800, and the bubble Reynolds number Reb∼1. Simulation parameters were chosen to match the experiment of Sanders et al. [J. Fluid Mech.552, 353 (2006)] investigating bubble-induced skin-friction drag reduction in a turbulent boundary layer, although the Reynolds number of the simulation is lower than the experiment. After injection, bubbles move away from the wall as they travel downstream with the flow. Mean bubble diffusion is compared to Sanders et al. and the passive scalar diffusion results given by Poreh and Cermak [Int. J. Heat Mass Transfer7, 1083 (1964)]. The mean diffusion profiles in the Sanders experiment and the simulation are comparable to the passive scalar results. Except very near the wall, the profiles of bubble concentration are also found to be similar to passive scalar results. The forces on a bubble were analyzed through budgets and the carrier-fluid acceleration was found to be the reason for moving the bubbles away from the wall.
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This work is supported by the United States Office of Naval Research under ONR Grant No. N00014-07-1-0420 with Dr. Ki-Han Kim as technical monitor. Computing resources were provided by the Arctic Research Supercomputing Center and the Minnesota Supercomputing Institute.
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