Non-equilibrium molecular motion and interface heat transfer in supersonic rarefied flows

Accurate modeling of non-equilibrium molecular motion is essential for understanding rarefied supersonic flows in the upper atmosphere. This study employs non-equilibrium molecular dynamics simulations to investigate the atomic-scale interactions of argon gas around a silicon cuboid under supersonic conditions across rarefied flow regimes. Through a systematic analysis of velocity distributions, collision dynamics, and interfacial heat transfer from free-molecular to transitional flow, the atomic mechanisms that govern rarefaction effects were uncovered. Results indicate that the non-equilibrium velocity distributions include contributions from both free-stream and disturbed gas flows. Rarefaction effects amplify under high-speed, low-density conditions due to insufficient molecular collisions within interaction timescales between gas flows. As the flow transitions from free-molecular to transitional flow regime, the stagnation-point heat flux exhibits a logarithmic deviation from free-molecular theory predictions as ambient pressure increases. This attenuation arises from the logarithmic accumulation of argon atoms near the surface, where number density initially linearly grows with pressure but saturates at a critical threshold (∼4.25 nm−3 for argon). At this limit, short-range repulsive forces from the Lennard-Jones potential override van der Waals attractions, which inhibits further atomic aggregation. This bridges nanoscale interactions to macroscale deviations, providing a predictive framework for aerodynamic performance and thermal management in rarefied supersonic environments.