Nonequilibrium magnetohydrodynamic flow in hypersonic rarefied environment

This paper presents a hybrid kinetic-fluid model for nonequilibrium, weakly ionized plasmas in magnetohydrodynamic (MHD) flow control applications. Heavy particles are treated kinetically as a single species, while the electron temperature is governed by a separate temperature equation. The kinetic component is solved using the unified gas-kinetic wave–particle (UGKWP) method, which captures flow physics across the rarefied-to-continuum regime. Applied to a transitional MHD flow, the model yields shock standoff distances in good agreement with experimental measurements. Analysis reveals two key rarefaction effects. First, nonequilibrium transport across the shock front allows high-energy particles to pre-heat the upstream region, elevating local electrical conductivity and increasing the standoff distance. Second, the electron temperature remains nearly constant across the shock, reducing conductivity and the resulting Lorentz force compared to predictions based on thermal equilibrium assumptions. These findings demonstrate that fluid-based methods fail to capture nonequilibrium physics, underscoring the need for multiscale kinetic solvers such as UGKWP for accurate prediction of MHD flow control in rarefied transitional regimes.