Non-equilibrium modelling of polyatomic gases: generic framework and 11-moment model

Abstract: In this study, we present a thermodynamically consistent framework for modelling polyatomic gases by integrating the \textit{general equation for non-equilibrium reversible-irreversible coupling} (GENERIC) with an 11-moment description. Our formulation unifies \textit{rational irreversible thermodynamics} (RIT) and \textit{extended irreversible thermodynamics} (EIT) into a single GENERIC-compatible structure that guarantees compliance with the second law of thermodynamics through the explicit construction of Poisson and friction matrices. By including translational and internal temperatures, as well as a temperature tensor, the model offers a well-structured and physically meaningful representation of non-equilibrium behavior in polyatomic gases. The entropy production is inherently non-negative, and all closure relations emerge naturally from thermodynamic principles. As a test of applicability, we compute the shock wave structure in nitrogen gas, validating the framework against Direct Simulation Monte Carlo (DSMC) simulations and experiments up to moderate Mach numbers.