Fundamentals of Gas Flows in Thermal Nonequilibrium Learned from a Model Constitutive Relation

Abstract

Constitutive relations of gas flows in thermal nonequilibrium can be derived by applying the moment method to the Boltzmann equation. In this work, a model constitutive relation developed on the basis of Eu's modified moment method is considered for the study of fundamentals of gas flows in thermal nonequilibrium. By solving basic problems such as the shock structure and shear flow, some fundamentals of gas flows in thermal non-equilibrium are identified; nonlinear, asymmetric and coupled relationship between stresses and rate of deformation, and effect of the bulk viscosity. Finally, issue of deriving continuum breakdown parameters is discussed in connection with developing a hybrid numerical code combining continuum and extended hydrodynamic or molecular approaches.