Modelling and analysis of high-enthalpy effects coupled with turbulence using direct numerical simulation

Abstract

Motivated by renewed interest in hypersonic flight, this work investigates the influence of thermo-chemical non-equilibrium on turbulent flows and evaluates key modelling approximations using scale-resolved simulations based on a multi-species compressible Navier–Stokes framework with finite-rate chemistry and multi-temperature formulations. Firstly, thermo-chemical non-equilibrium effects were examined through simulations of free shear mixing layers. Two-dimensional simulations showed reductions in turbulent kinetic energy of up to 8% under non-equilibrium conditions. In three-dimensional mixing layers, Reynolds stresses were largely unaffected; however, analysis of additional vibrational energy flux terms revealed that thermal non-equilibrium suppresses vibrational fluctuations due to weakened coupling between translational and vibrational modes. To support efficient high-enthalpy scale-resolved simulations, a streamlined viscosity and thermal conductivity model for air mixtures over 100–9000K was developed. Compared with existing efficient formulations, the proposed model demonstrated improved accuracy under strongly non-equilibrium conditions, while achieving computational cost reductions of up to 45% in two-dimensional and 58.5% in three-dimensional simulations relative to the benchmark model. Finally, turbulent channel-flow simulations under thermo-chemical non-equilibrium were performed to assess high-enthalpy effects in a canonical wall-bounded configuration. Strong near-wall temperature gradients indicated thermally frozen behaviour. While thermal non-equilibrium had minimal impact on mean flow statistics, chemical non-equilibrium led to reduced local Mach number and temperature fluctuations due to steep nitrogen mass-fraction gradients. Overall, this study provides a systematic assessment of thermo-chemical non-equilibrium effects on turbulence across canonical flow configurations and establishes a robust foundation for high-fidelity modelling of high-enthalpy turbulent flows.

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Identifiers

ORCID for Ali Musawi: orcid.org/0000-0002-1975-4270

ORCID for Neil Sandham: orcid.org/0000-0002-5107-0944

ORCID for Minkwan Kim: orcid.org/0000-0002-6192-312X

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