neqFoam: An OpenFOAM-based Solver with a Unified Approach for the Thermochemical Non-Equilibrium Simulations
Description
Given the growing emphasis on hypersonic propulsion systems, accurate prediction of thermochemical non-equilibrium phenomena has become paramount. However, the thermodynamic models used to simulate combustion and thermal non-equilibrium flows in hypersonic regimes differ substantially. The simple partition-function model–predominantly applied in thermal non-equilibrium simulations–relies on rigid-rotor and harmonic-oscillator approximations that neglect key molecular energy interactions, whereas polynomial representations of thermodynamic properties–widely employed in combustion simulations–incorporate additional correction factors to account for detailed molecular and atomic energy modes. In this paper, we introduce a novel OpenFOAM-based solver for a unified approach to thermochemical non-equilibrium flows using a polynomial representation. This contrasts with most prior work, which applies polynomial representations to combustion but relies on the simple partition-function model for thermal non-equilibrium flows. Notably, this solver implements a damped Newton–Raphson method to enhance numerical stability and convergence during temperature evaluations. We first analyzed the differences between these thermodynamic models and their respective impacts on predicted properties. Subsequently, we performed numerical simulations for a 0-D heat bath, the LENS-XX double cone, and a shock-induced combustion case. The results demonstrate that, the polynomial representation–incorporating detailed molecular energy modes at lower computational cost–exhibits pronounced differences in thermodynamic properties relative to the simple partition-function model, demonstrating superior suitability for thermochemical non-equilibrium flow analysis.