(51g) Lattice-Boltzmann Phase-Field Modeling of Multiphase Flows Including Phase Change

In this presentation, we will discuss lattice-Boltzmann methods (LBM) based on phase-field models for representing the dynamics of multiphase flows at high density contrasts including phase change. The LBM is based on the foundations of kinetic theory and is emerging as an alternative to the conventional CFD methods. It involves the solution of the lattice Boltzmann equation (LBE), which describes the evolution of distribution of particle populations that are modified by the advection, or streaming along discrete directions, and collisions occurring on a lattice. With the underlying lattice respecting sufficient symmetry properties, the collective behavior of such particle populations represents the dynamics of fluid flow. Computational assets of the LBM include its simplicity, essentially local character of its procedure which circumvents the solution of time consuming elliptic equation for the pressure field that arise in conventional CFD projection methods, and its inherently parallel nature of the algorithm offering almost linear scalability on a variety of parallel computers. From a physical standpoint, since LBE represents processes at sub-macroscopic scales, models for complex fluids including multiphase flows can be naturally incorporated. Thus the LBM is well suited for computing large problems involving complex fluid flows. An important means for representing various aspects of interfacial physics is through phase-phase models that are based on thermodynamic principles. In particular, they allow systems to evolve to minimize free energy functionals with respect to order parameters that serve as phase indicators, which vary sharply but continuously across interfaces, thereby endowing them with finite thickness and interfacial tension. These models are particularly suited for interface capturing and development through the collision-streaming algorithms at the heart of LBMs. They also allow circumventing the instability problems at high phase-densities that limit other existing models for multiphase flows in LBMs, which are important for practical applications. We will discuss the development of a LBM for multiphase flows including phase change at high density ratios, which is based on a phase-field model that also incorporates phase change effects, and its validation for some canonical problems.