耦合界面力的两相流相场格子Boltzmann模型

提出了一种改进的基于相场理论的两相流格子Boltzmann模型.通过引入一种新的更加简化的外力项分布函数，使得此模型克服了前人工作中界面力尺度与理论分析不一致的问题，并且通过Chapman-Enskog多尺度分析表明，所提出的模型能够准确恢复到追踪界面的Cahn-Hilliard方程和不可压的Navier-Stokes方程，并且宏观速度的计算更为简化.利用所提模型对几个经典两相流问题，包括静态液滴测试、液滴合并问题、亚稳态分解以及瑞利-泰勒不稳定性进行了数值模拟，发现本模型可以获得量级为10^-9极小的虚假速度，并且这些算例获取的数值解与解析解或已有的文献结果相吻合，从而验证了模型的准确性和可行性.最后，利用所发展的两相流格子Boltzmann模型研究了随机扰动的瑞利-泰勒不稳定性问题，并着重分析了雷诺数对流体相界面的影响.发现对于高雷诺数情形，在演化前期，流体界面出现一排“蘑菇”形状，而在演化后期，流体界面呈现十分复杂的混沌拓扑结构.不同于高雷诺数情形，低雷诺数时流体界面变得相对光滑，在演化后期未观察到混沌拓扑结构.

Phase field lattice Boltzmann model for two-phase flow coupled with additional interfacial force

The phase field model has become increasingly popular due to its underlying physics for describing two-phase interface dynamics. In this case, several lattice Boltzmann multiphase models have been constructed from the perspective of the phase field theory. All these models are composed of two distribution functions: one is used to solve the interface tracking equation and the other is adopted to solve the Navier-Stokes equations. It has been reported that to match the target equation, an additional interfacial force should be included in these models, but the scale of this force is found to be contradictory with the theoretical analysis. To solve this problem, in this paper an improved lattice Boltzmann model based on the Cahn-Hilliard phase-field theory is proposed for simulating two-phase flows. By introducing a novel and simple force distribution function, the improved model solves the problem that the scale of an additional interfacial force is not consistent with the theoretical one. The Chapman-Enskog analysis shows that the present model can accurately recover the Cahn-Hilliard equation for interface capturing and the incompressible Navier-Stokes equations, and the calculation of macroscopic velocity is also more efficient. A series of classic two-phase flow examples, including static drop test, droplets emerge, spinodal decomposition and Rayleigh-Taylor instability is simulated numerically. It is found that the numerical solutions agree well with the analytical solutions or the existing results, which verifies the accuracy and feasibility of the proposed model. In addition, the Rayleigh-Taylor instability with the imposed random perturbation is also simulated, where the influence of the Reynolds number on the evolution of the phase interface is analyzed. It is found that for the case of the high Reynolds number, a row of “mushroom” shape appears at the fluid interface in the early stages of evolution. At the later stages of evolution, the fluid interface presents a very complex chaotic topology. Unlike the case of the high Reynolds number, the fluid interface becomes relatively smooth at low Reynolds numbers, and no chaotic topology is observed at any of the later stages of evolution.