Impact of outlet boundary condition schemes for the lattice Boltzmann method regarding the Stefan phase-change problem

Abstract

In several industrial applications, there are systems that depend on multiphase flows. Consequently, modelling these processes are very attractive for the scientific community. Having a mesoscopic nature, the lattice Boltzmann method (LBM) presents advantages to deal with complex geometries and complex processes, such as bubble merging, fluid-structure interaction, etc. Several LBM models for multiphase flows were developed by the research community. Usually, in the applications of multiphase flows, there are open boundaries where the fluid with more than one phase leaves the domain. However, there are few works in the literature regarding the impact of the BC schemes with the Allen-Cahn-based phase-field LBM, especially considering liquid-gas phase change. Then, in this work, we explore the impact of three schemes of open BC: the equilibrium scheme, the extrapolation scheme, and the convective BC scheme. First, the impact of the BC schemes on a channel flow with a bubble inside is studied. Next, the Stefan problem considering real properties (saturated HFE7100) is simulated. The results showed that both the extrapolation and equilibrium schemes can introduce instabilities and incoherences in the results, while the convective BC is the one that better conserves the coherence of the results.

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