Abstract This study investigates elbow effects on single-phase and two-phase flows. ANSYS CFX is used to simulate the evolution of the single-phase velocity distribution and two-phase interfacial structure downstream of vertical elbows. Simulations are benchmarked with existing LDA data and detailed four-sensor conductivity probe data. It is found that elbows create secondary flow, containing two counter-rotating vortices in both single-phase and two-phase flows. The vortices shift to pipe center and develop into parabolic velocity profile downstream. The elbow effect dissipates exponentially and dissipates 90% of its initial maximum value at approximately 11D downstream, no matter the elbow direction. In two-phase flow, bubbles are entrained by the secondary flow to form double-peaked void fraction and interfacial area concentration distributions. The double-peaked distribution moves upward and becomes single-peaked distribution downstream. Due to the additional buoyant force, the elbow effect takes much longer length to dissipate in two-phase flow than in single-phase flow.

中文翻译：

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横过 90° 垂直弯头的单相和两相流的数值模拟

摘要 本研究调查了弯管对单相和两相流的影响。ANSYS CFX 用于模拟垂直弯头下游的单相速度分布和两相界面结构的演变。模拟以现有 LDA 数据和详细的四传感器电导率探头数据为基准。发现弯头产生二次流，在单相流和两相流中都包含两个反向旋转的涡流。涡流移动到管道中心并在下游发展成抛物线速度剖面。肘部效应以指数方式消散，并在下游大约 11D 处消散其初始最大值的 90%，无论肘部方向如何。在两相流中，气泡被二次流夹带形成双峰空隙率和界面面积浓度分布。双峰分布向上移动，下游变为单峰分布。由于额外的浮力，肘效应在两相流中比在单相流中消散的时间长得多。