The coupling of the Navier-Stokes equations with the Allen-Cahn model represents a significant advance in the field of fluid mechanics and interface modeling. This development has its roots in the need to better understand and simulate complex multi-phase fluid dynamics.

This book (Complex Fluid Dynamics: Approaches with Allen-Cahn and Navier-Stokes) explores the approximation of dynamics between two fluids of different densities and viscosities. It presents a model that couples the Allen-Cahn equation, describing the evolution of a scalar-order parameter, with the time-dependent Navier-Stokes equations governing fluid motion.

This coupling involves a surface tension term, which takes into account the energy required to create an interface between phases, proportional to the curvature of the interface, leading to the formation of a dynamic interface. The two-phase Navier-Stokes/Allen-Cahn equations simulate several fluid flows, using the Allen-Cahn model for diffuse interfaces and the Navier-Stokes equations for fluid dynamics.

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