Hydrodynamic limits of kinetic equations for polyatomic and reactive gases

Starting from a kinetic BGK–model for a rarefied polyatomic gas, based on a molecular structure of discrete internal energy levels, an asymptotic Chapman–Enskog procedure is developed in the asymptotic continuum limit in order to derive consistent fluid–dynamic equations for macroscopic fields at Navier–Stokes level. In this way, the model allows to treat the gas as a mixture of mono–atomic species. Explicit expressions are given not only for dynamical pressure, but also for shear stress, di↵usion velocities, and heat flux. The analysis is shown to deal properly also with a mixture of reactive gases, endowed for simplicity with translational degrees of freedom only, in which frame analogous results can be achieved.