Simulation of shock induced vapor condensation flows in the Lennard-Jones fluid by microscopic and continuum models

The vapor condensation onto a thin liquid film, induced by the reflection of a weak shock wave, is studied by molecular dynamics atomistic simulations of a simple Lennard-Jones fluid. Molecular dynamics results provide reference flowfields for two models. The first one adopts a hybrid continuum-kinetic description in which the liquid phase is described by hydrodynamic equations, whereas the vapor is described by the Boltzmann equation. The structureless liquid-vapor interface is replaced by a classical kinetic boundary condition. The second model is based on the diffuse interface full continuum description of the Lennard-Jones fluid liquid, vapor, and interface regions. For both models, the required fluid thermodynamic and transport properties have been prescribed according to those of the Lennard-Jones fluid. Not unexpectedly, the results show that the continuum-kinetic model provides a good description of molecular dynamics results when the vapor is close to ideal conditions, increasingly deviating from reference data when the vapor non-ideality increases. The opposite behavior is found for the diffuse interface model. It is observed that flow conditions exist where both models fail to provide a reasonably accurate description of reference flow properties.