Effects of Hypersonic Flight Conditions on Stagnation-Point Magnetohydrodynamic Heat-Flux Reduction

Magnetohydrodynamic flow control can mitigate stagnation-point heating in hypersonic flight, but the incremental benefit of increasing magnetic-field strength decreases as the interaction is intensified, giving rise to a saturation trend. This study used a stagnation-point boundary-layer model to determine how flight velocity, freestream pressure, and wall catalyticity govern this behavior. The heat-flux response is analyzed in terms of the boundary-layer-edge velocity gradient, heat transfer function, and species diffusion. The reduction in velocity gradient provides the primary contribution to heat-flux mitigation, whereas the increase in the heat transfer function progressively offsets this benefit as the magnetic field is strengthened. For noncatalytic walls, higher flight velocity and lower freestream pressure strengthen the magnetic-field-induced reduction in the edge velocity gradient, thereby enhancing the initial heat-flux mitigation. However, they also intensify the increase in the heat transfer function, causing the incremental benefit to decline earlier. A fully catalytic wall alters the enthalpy distribution of the gas near the wall and introduces a finite species-diffusion contribution, producing strongly condition-dependent effects. These results establish a boundary-layer-based mechanism for the saturation trend and provide an aerothermal basis for selecting condition-dependent magnetic-field ranges.