Three-dimensional discrete Boltzmann models for compressible flows in and out of equilibrium

We present a series of three-dimensional discrete Boltzmann models for compressible flows in and out of equilibrium. The key formulating technique is the construction of discrete equilibrium distribution function through inversely solving the kinetic moment relations that it satisfies. The crucial physical requirement is that all the used kinetic moment relations must be consistent with the non-equilibrium statistical mechanics. The necessity of such a kinetic model is that, with increasing the complexity of flows, the dynamical characterization of non-equilibrium state and the understanding of the constitutive relations need higher order kinetic moments and their evolution. The discrete Boltzmann models at the Euler and Navier–Stokes levels proposed by this scheme are validated by several well-known benchmarks, ranging from one-dimension to three-dimension. Particularly, when the local Mach number, temperature ratio, and pressure ratio are as large as 102, 104, and 105, respectively, the simulation results are still in excellent agreement with the Riemann solutions. How to model deeper thermodynamic non-equilibrium flows by discrete Boltzmann is indicated. Via the discrete Boltzmann method, it is convenient to simulate nonequilibrium flows without knowing exact form of the hydrodynamic equations.