Evaluating dynamic magnetic fields in hypersonic flight

Spacecraft reentering Earth’s atmosphere are exposed to high temperatures and pressures caused by hypersonic flight. Typically, those spacecraft are protected from these environmental conditions via heat shields, which are comprised of ablative materials that must be frequently replaced.

A promising alternative is magnetohydrodynamic (MHD) flow control, using superconducting magnets to redirect plasma and protect the hull. Kim et al. modeled the interactions between an applied magnetic field and a hypersonic shock layer at high magnetic Reynolds numbers.

“Many hypersonic MHD studies rely on a low magnetic Reynolds number approximation that treats the magnetic field as essentially fixed,” said author Hojun You. “However, recent evidence suggests that the magnetic Reynolds number can exceed unity within shock layers in realistic reentry, exactly where electromagnetic forces are most consequential. This raises a fundamental concern: If the field is actually deformed by the plasma motion, then both force and energy could be mispredicted.”

The authors employed a thermochemical nonequilibrium three-temperature model to obtain a consistent electron temperature and conductivity, and a resistive MHD model to calculate magnetic field distortion caused by magnetic convection and diffusion. This combination allowed them to determine the Lorentz force, Lorentz work, and Joule heating in this dynamic regime.

They found that at magnetic Reynolds numbers approaching or exceeding unity — where the system is dominated by convection effects — magnetic field deformation becomes a significant effect.

“The most striking difference is that low magnetic Reynolds number treatments can significantly overpredict the Lorentz force when applied outside its validity range because it neglects induced-field dynamics and associated energy pathways,” said You.

The authors plan to improve their models by introducing more accurate upstream effects, simulating more complex geometries, and comparing their results with experimental measurements.

Source: “Electromagnetic effects of magnetic field deformation on a hypersonic shock,” by Chanho Kim, Jae Gang Kim, Kyu Hong Kim, and Hojun You, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0321538 .