Abstract This paper analyses the local and time-dependent behavior of large-scale structures responsible for liquid circulation in gas-water flow of a 3-D cylindrical bubble column of high aspect ratio with a multiple orifice for uniform aeration. The large-scale flow structures play an important role in the mixing and the mass transfer while coherent structures dominate hydrodynamic characteristics of the turbulent flow field. A three-dimensional Euler-Euler large eddy simulation (LES) model was used to calculate large-scale structures and their interaction with bubbles at inlet superficial gas velocities of U G = 6 and 8.4 cm/s where vortical-spiral and turbulent flow regimes occur. The two-phase model gives good agreements with experimental measurements. We use a conditional sampling procedure of liquid velocity and gas hold-up time series to identify and educe the development of coherent flow structures which consists in a pair of counter-rotating vortices convected in a staggered pattern along the column in both the vortical-spiral and central plume regions. On average, the detected instantaneous events for each template account for about 12–15% of the data recorded and may appear simultaneously. These events produce important fluctuations in the axial liquid velocity and gas void fraction. The sampling procedure yielded the averaged topology of the three-dimensional large-scale structures which was visualized using isosurfaces of the vorticity for different gas flow rates. The structures have spiral tube-shaped topology rotating along the column near the walls with a pair of counter-rotating cells sustained through the flow. This work provides deep insights into turbulent flow field in gas-liquid bubble column by LES and pattern recognition.

中文翻译：

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3D泡罩塔反应器中的瞬态大规模两相流结构

摘要 本文分析了大型结构在气-水流中负责液体循环的大型结构的局部和时间相关行为，该结构具有多孔的均匀曝气，具有高纵横比的 3-D 圆柱形气泡柱。大尺度流动结构在混合和传质中起重要作用，而相干结构在湍流流场的流体动力学特性中占主导地位。三维 Euler-Euler 大涡模拟 (LES) 模型用于计算大型结构及其与气泡的相互作用，入口表观气体速度为 UG = 6 和 8.4 cm/s，其中发生涡旋和湍流流态. 两相模型与实验测量结果非常吻合。我们使用液体速度和气体滞留时间序列的条件采样程序来识别和推断连贯流动结构的发展，该结构由一对反向旋转的涡流组成，这些涡流在两个涡旋涡旋中沿柱以交错模式对流和中央羽流区域。平均而言，每个模板检测到的瞬时事件约占记录数据的 12-15%，并且可能同时出现。这些事件在轴向液体速度和气体空隙率方面产生重要波动。采样过程产生了三维大型结构的平均拓扑结构，使用不同气体流速的涡度等值面进行可视化。这些结构具有螺旋管状拓扑结构，沿着靠近壁的柱子旋转，一对反向旋转的细胞通过流动维持。这项工作通过 LES 和模式识别提供了对气液气泡柱湍流场的深入见解。