RANS simulation of bubble coalescence and break-up in bubbly two-phase flows
RANS simulation of bubble coalescence and break-up in bubbly two-phase flows
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DOI：
10.1016/j.ces.2016.02.034
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发表时间：
2016-06
影响因子：
4.7
通讯作者：
M. Colombo;M. Fairweather
中科院分区：
文献类型：
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作者：
M. Colombo;M. Fairweather
在泡状流中，气泡尺寸分布决定了可用于相间转移过程的界面面积，因此，了解气泡群的行为和平均特征对于预测这些类型的流是至关重要的。本文采用STAR-CCM+程序，将S γ粒子数平衡模型与欧拉-欧拉双流体模型耦合，并对上升泡状管流进行了数值模拟。基于气泡尺寸分布的矩的S γ模型跟踪了气泡破裂和合并过程中气泡尺寸的变化。采用改进的聚并源，获得了气泡平均直径、速度和含气率径向分布的良好精度。数值结果表明，更好的预测时，这些流量被认为是合并为主，但是，尽管如此，需要更多的知识，包括所有可能的负责机制的合并和分裂模型的发展进展。在这方面，有一个实验数据的要求，将允许验证预测的气泡直径分布和连续相中的湍流强度，这对聚结和破裂模型有显着的影响。该模型的一个高级版本，其中包括雷诺应力湍流制剂和两组气泡占球形气泡的相反行为，积累接近管壁，帽气泡，向管中心迁移，提出。雷诺应力模型被发现，以更好地处理湍流和相间力之间的相互作用，和使用只有两个气泡组似乎足以描述整个气泡谱和泡状流状态的过渡段塞流。
In bubbly flows, the bubble size distribution dictates the interfacial area available for the interphase transfer processes and, therefore, understanding the behaviour and the average features of the bubble population is crucial for the prediction of these kinds of flows. In this work, by means of the STAR-CCM+ code, theSγpopulation balance model is coupled with an Eulerian–Eulerian two-fluid approach and tested against data on upward bubbly pipe flows. TheSγmodel, based on the moments of the bubble size distribution, tracks the evolution of the bubble sizes due to bubble break-up and bubble coalescence. Good accuracy for the average bubble diameter, the velocity and the void fraction radial profiles is achieved with a modified coalescence source. Numerical results show that better predictions are obtained when these flows are considered to be coalescence dominated, but, nevertheless, additional knowledge is required to progress in the development of coalescence and break-up models that include all the possible responsible mechanisms. In this regard, there is a requirement for experimental data that will allow validation of both the predicted bubble diameter distribution and the intensity of the turbulence in the continuous phase which has a significant impact on coalescence and break-up models. An advanced version of the model, that includes a Reynolds stress turbulence formulation and two groups of bubbles to account for the opposite behaviour of spherical bubbles, which accumulate close to the pipe wall, and cap bubbles, that migrate towards the pipe centre, is proposed. The Reynolds stress model is found to better handle the interactions between the turbulence and the interphase forces, and the use of only two bubble groups seems sufficient to describe the whole bubble spectrum and the bubbly flow regime up to the transition to slug flow.