Numerical Analysis of Droplet Flow Regime in Gas-Liquid Two-Phase Flow using Particle Method

双流体模型用于气液两相流分析。气相和液相的控制方程用表示界面相互作用的关系式同时求解。这些相关性是通过实验得到的。数值分析对它们来说是困难的。其中，界面面积是决定相互作用的重要参数。在颗粒法中不需要网格，因此可以分析流体的破碎和聚并以及界面的大变形。在本研究中，用粒子法分析了液滴流态中计算界面面积的临界韦伯数。本文采用的粒子法是本研究人员提出的运动粒子半隐式（MPS）方法。建立了一种新的表面张力模型来分析单液滴的行为。计算了方形液滴的振动，振动周期与解析解一致。计算了液滴周围的流动，液滴上的压力分布与以往的研究结果一致。液滴破碎受压力分布驱动，受表面张力抑制。这两个过程都经过验证。为了准确地分析液滴的行为，需要超过100个粒子。众所周知，液滴的破碎是由一个叫做韦伯数的无量纲数控制的，它是驱动力与抑制力的比值。临界韦伯数给出了液滴破碎的极限。当韦伯数低于临界值时，不发生破裂。用MPS方法计算了不同韦伯数下的液滴行为。结果表明，临界韦伯数为13。这与实验数据一致。因此，可以得出结论，MPS方法可以成功地分析临界韦伯数。

Two-fluid model has been used for gas-liquid two-phase flow analysis. Governing equations of gas and liquid phases are simultaneously solved with correlations expressing interfacial interactions. These correlations are obtained by experiments. Numerical analysis is difficult for them. In particular, interfacial area is an important parameter to determine the interactions. Grids are not necessary in particle method, so that fragmentation and coalescence of fluids as well as large deformation of interfaces can be analyzed. In the present study, the critical Weber number by which the interfacial area is evaluated in the droplet flow regime is analyzed by the particle method.The particle method used here is MPS (Moving Particle Semi-implicit) method which has been developed by the present researcher. A new model for surface tension is developed to analyze single droplet behavior. Vibration of a square droplet is calculated and the oscillating period agrees with that of the analytical solution. Flow around a droplet is calculated and the pressure distribution on the droplet agrees with those of the past studies. Droplet breakup is driven by the pressure distribution and suppressed by surface tension. Both processes are verified. It is also clarified that more than 100 particles are necessary to analyze the droplet behavior accurately.It is known that the droplet breakup is governed by a non-dimensional number called Weber number, which is the ratio of the driving force to the suppressing force. Critical Weber number gives the limit of droplet breakup. The breakup does not occur when the Weber number is below the critical value. The droplet behavior is calculated for various Weber numbers using the MPS method. The results show that the critical Weber number is 13. This agrees with experimental data. Therefore, it is concluded that the critical Weber number is successfully analyzed by the MPS method.