Development of a one-dimensional gas-liquid two-phase flow model for whole flow regime in a vertical pipe

虽然时空演化是垂直管内气液两相流最本质的特性之一，但目前还没有有效的数值方法来预测流型的空间演化和转变。详细的数值方法，如界面跟踪方法，可以预测详细的相分布，发挥主导作用的空间演变。然而，这些方法需要模型或假设的空间演变过程，如气泡聚结和集群，和这些方法的应用到工业设计是不现实的，由于巨大的CPU时间。本文旨在建立一个适用于垂直管道内全流型的一维气液两相流模型。为了弥补空间演化数据库的不足，本文进行了垂直管内两相流实验，研究了体积平均含气率的空间演化、含气率波动以及由此引起的流型演化 关于我们 根据实验结果建立了气泡聚集和合并的空间演化唯象模型，并利用该模型对一维单向气泡跟踪进行了模拟和评价，实验证实：（1）流型的空间演化主要取决于气泡分布而不是平均含气率，（2）气泡聚团在气泡的演化过程中起主导作用;（3）剪切诱导湍流的存在阻碍了气泡的聚并和聚团，但随着含气率的增加，聚并和聚团的作用增强;（4）气泡团的上升速度与相同尺寸的Taylor气泡的上升速度几乎相等，（5）随着液体流量的减小，大气泡后的尾迹对小气泡运动的影响增大;（6）气泡团和Taylor气泡的生长使气泡脉动沿流动方向沿着增大。所开发的模拟方法包括气泡径向分布的模型，并且模拟的时间与实际现象几乎相同。模拟得到的流型演化、平均含气率和含气率波动与滞止液两相流、层流和湍流实验结果吻合较好。少

Though a space-time evolution is one of the most intrinsic natures of gas-liquid two-phase in a vertical pipe, there is little available numerical method for the prediction of the spatial evolution and the transition of flow regime. Detailed numerical methods such as an interface tracking method can predict detailed phase distributions, which play a dominant role on spatial evolution. These method however need models or assumptions on processes of spatial evolution such as bubble coalescence and clustering, and the application of these method to industrial design is not realistic due to the huge CPU time. The purpose of the present study is to develop a one-dimensional gas-liquid two-phase flow model for whole flow regime in a vertical pipe. In order to make up for the lack of database on spatial evolution, we carried out two-phase flow experiments in a vertical pipe, and investigated spatial evolution of volume-averaged void fraction, void fluctuation and flow pattern evolution caused … More by the bubble clustering and coalescence Phenomenological models for the spatial evolution were developed through the experimental results, and one-dimensional one-way bubble tracking simulation with these models was developed and evaluated.It was confirmed through the experiments that (1) the spatial evolution of flow pattern is dominated by the bubble distributions rather than the mean void fraction, (2) bubble clustering plays a dominant role in the evolution, (3) bubble coalescence and bubble clustering are hindered by the presence of shear-induced turbulence, but they are enhanced with increasing the void fraction, (4) the rising velocity of a bubble cluster is almost equal to that of a Taylor bubble in the same size, (5) the impact of wake behind large bubble on the motion of small bubbles increases with decreasing the liquid flow rate, and (6) the void fluctuation increases along the flow direction due to the growth of bubble clusters and Taylor bubbles.Phenomenological models were developed based on the experimental results, and applied them to one-dimensional bubble tracking method. The developed simulation method includes a model of radial distribution of bubbles, and the time for the simulation is almost the same with the actual phenomena. The simulated flow pattern evolution, averaged void fraction and void fluctuation were agree well with the experimental results of two-phase flow in stagnant liquid, laminar and turbulent liquid flow. Less