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A DNS study of laminar bubbly flows in a vertical channel

机译：垂直通道中层状气泡流的DNS研究

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Direct numerical simulations are used to examine laminar bubbly flows in vertical channels. For equal size nearly spherical bubbles the results show that at steady state the number density of bubbles in the center of the channel is always such that the fluid mixture there is in hydrostatic equilibrium. For upflow, excess bubbles are pushed to the walls, forming a bubble rich wall-layer, one bubble diameter thick. For downflow, bubbles are drawn into the channel center, leading to a wall-layer devoid of bubbles, of a thickness determined by how much the void fraction in the center of the channel must be increased to reach hydrostatic equilibrium. The void fraction profile can be predicted analytically using a very simple model and the model also gives the velocity profile for the downflow case. For the upflow, however, the velocity increase across the wall-layer must be obtained from the simulations. The slip velocity of the bubbles in the channel core and the velocity fluctuations are predicted reasonably well by results for homogeneous flows. (c) 2006 Elsevier Ltd. All rights reserved.
机译：直接数值模拟用于检查垂直通道中的层状气泡流。对于相等大小的几乎球形的气泡，结果表明，在稳态下，通道中心的气泡数密度始终使得流体混合物处于静水平衡状态。为了向上流动，将多余的气泡推向壁，形成一个气泡丰富的壁层，其直径为一个气泡的厚度。对于向下流动，气泡被吸入通道中心，导致没有气泡的壁层的厚度由必须增加通道中心的空隙率以达到静水平衡确定。可以使用一个非常简单的模型来分析预测孔隙率分布，该模型还给出了下流情况下的速度分布。但是，对于上流，必须从模拟中获得穿过壁层的速度增加。通过均匀流动的结果，可以很好地预测通道芯中气泡的滑动速度和速度波动。 （c）2006 Elsevier Ltd.保留所有权利。

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