Interface dynamics in two-phase flows with diffuse interface methods

Abstract

Diffuse interface methods are an approach to modeling dynamic multiphase systems. The method allows keeping track of domains of phases and assign physical tension to interfaces in between. In this thesis, two diffuse interface methods are applied to study two different kinds of problems. One is a coarse phase field model of slow dynamics on large scales, and the other a hydrodynamics model of fast dynamics on microscopic scales. The basis of the phase field model is slow flow of mass on large scales. The model was considered in relation to the experimental Hele-Shaw cell setup. We studied statistics of a propagating interface as it undergoes kinetic roughening due to disorder. Good match was found between the models and the Hele-Shaw setup, but results from both the models and the experiments suggest against a universality class these minimal model systems would potentially represent. A model of thermal hydrodynamics to study boiling at the microscale was also considered. A method that enables imposing a constant external pressure to the system was developed. The major component of the method is a novel open boundary condition. We verify the method with numerical test cases, and observe the microscale dynamics of nucleate boiling and film boiling under constant pressure. We find a complex flow pattern at the three phase contact line of a growing bubble, which is consistent with the vapor recoil theory of boiling crisis.