Recent DNS studies of bubbly flows in channels are discussed. Simulations of nearly spherical bubbly flows in vertical channels show that the bubbles move towards the wall for upflow and away from the wall for downflow in such a way that the core is in hydrostatic equilibrium. For down flow the wall layer is free of bubbles but for upflow there is an excess of bubbles in the wall layer. The liquid velocity in the core is uniform. For laminar downflow the velocity in the wall layer can be computed analytically but for upflow the velocity is strongly influenced by the presence of the bubbles. Results for turbulent flow show similar behavior and for downflow the velocity is given (almost) by the law of the wall. Several simulations are used to examine the effect of void fraction and bubble size for turbulent downflow.

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