Kai Luo

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.

This study employs mid-infrared tunable diode laser absorption spectroscopy (TDLAS) combined with transient computational fluid dynamics (CFD) to characterize unsteady and nonuniform airflow at the nozzle exit of the detonation-driven JFX reflected shock tunnel at the Chinese Academy of Sciences. Three NO rovibrational transitions and two [Formula: see text] transitions were scanned by two quantum cascade lasers at 5.2 and [Formula: see text] to retrieve temperatures and partial pressures. Test gas purity and an annular gas-bleed arrangement were used to mitigate water contamination. Dehydrated synthetic air had an essentially imperceptible effect, while the gas-bleed device extended the contamination-free measurement window from 200 to [Formula: see text], during which the flow remains highly unsteady. The observed mismatch between translational and rotational temperatures is attributed to Doppler shift effects from strong expansion, with deviations of up to 56.9% of the rotational temperature. Simulated path-averaged rotational temperatures agreed closely with TDLAS results when NO exchange and [Formula: see text] dissociation rates were increased by an order of magnitude relative to Park’s model. In contrast, TDLAS-derived vibrational temperatures showed limited agreement with the simulated species-averaged vibrational temperature, and simulated NO partial pressures were roughly twice the measured values.

To investigate the effect of a magnetic field on the stagnation-point boundary layer in hypersonic flows, this study developed a magnetohydrodynamic boundary-layer model that incorporates real gas effects. Variations in the boundary layer, including stagnation-point heat flux, heat transfer function, and skin friction function, were examined to elucidate the mechanisms associated with different boundary-layer-edge conditions. Parameters at the boundary-layer edge were obtained using the quasi-one-dimensional stagnation streamline method. The results indicate that the nonequilibrium state at the boundary-layer edge has minimal impact on the inner boundary layer. In contrast, the magnetic strength reduces convective heat transfer primarily by decreasing the velocity gradient at the boundary-layer edge. The enhancement of the heat transfer function is mainly driven by the “acceleration effect” on the flow within the boundary layer, resulting from decreased velocity gradients and increased Lorentz force. This interaction ultimately leads to a saturation effect in the reduction of heat transfer. Additionally, the increase in the skin friction function is primarily due to velocity overshoot within the boundary layer induced by the magnetic field. The Lorentz force induced by the magnetic field expands the inviscid shock layer while simultaneously reducing the boundary-layer thickness. Overall, the stagnation-point boundary-layer model developed in this study not only facilitates rapid assessment of stagnation parameters, but also deepens our understanding of the magnetic field’s role within the stagnation-point boundary layer.

The ablation product carbon dioxide (CO2) around the hypersonic vehicle may become an important source of radiation. Accurate simulation of the chemical reaction process between CO2 and air is of great significance for the design of thermal protection systems. A combination of ground experiments and numerical simulations is used in this study to investigate the reaction process of CO2–air mixtures with different proportions behind shock waves with velocities ranging from 3.6 to 4.1 km/s. Flow parameters are simulated based on the two-temperature (2-T) model and the Lee and Park chemical reaction mechanism, and the laser absorption spectroscopy measurements are carried out on the Φ800 mm shock tube at the Chinese Academy of Sciences, Institute of Mechanics, to obtain time-resolved post-shock gas temperatures and partial pressures of CO2 and carbon monoxide (CO). Measurement results indicate that the post-shock temperature is much higher than the equilibrium value when it is close to the shock front and then gradually develops towards equilibrium. The partial pressure of CO2 shows the same trend as temperature. Comparisons between experimental results and calculated results show that the used model can accurately predict the post-shock temperature. When the initial CO2 volume fraction is below 50%, the model underestimates the CO2 dissociation rate, meaning that the actual CO2 content is lower than the calculated value and the CO content is higher. Conversely, when the CO2 volume fraction is greater than or equal to 50%, the prediction of the CO2 dissociation rate tends to be overestimated.

Transverse jets have been effectively employed for attitude/orbit control within the aerospace applications. However, there is a paucity of experimental data on the flow characteristics of transverse jet interaction with hypersonic crossflows at high flight attitudes, particularly those associated with low-density and high-temperature conditions. This study aims to experimentally investigate the flow characteristics of transverse jets in a hypersonic crossflow using a flat-plate model. Schlieren imaging, nitric oxide planar laser-induced fluorescence (NO-PLIF) imaging, and pressure transducer techniques are employed to visualize flow structures and conduct parametric measurements. Numerical simulations are conducted to shed light on the flow structures and elucidate the underlying mechanisms as well. The results indicate that NO-PLIF imaging can effectively capture the spatially resolved structures surrounding the jet exit. Both the Mach disk height and barrel shock width are positively correlated with the jet momentum ratio [ ] and angle of attack [ ]. Furthermore, the pressure plateau and peak distribution upstream and downstream of the sonic orifice are also significantly influenced by [ ] and [ ]. Specifically, peak pressure increases with an increase in [ ], while it drops for a larger [ ]. These results enhance our understanding of flow characteristics of transverse jet interactions in low-density, high-temperature hypersonic crossflows and provide validations for subsequent numerical simulations.

High enthalpy shock tunnel is a critical ground testing facility for evaluating the aerodynamic performance of hypersonic vehicles by simulating high-enthalpy, hypersonic flows. However, as the total temperature or pressure of the stagnant gas rises, the throat insert may be subjected to melting or oxidation, leading to a degradation in flow quality or a reduction in effective test time. This study investigates the unsteady heat transfer between the gas flow and the throat insert using a conjugate heat transfer model. The effects of test time, total temperature, and total pressure on the throat temperature are presented. An increase in any of these factors will raise the throat temperature. Moreover, oxidation will cause the copper throat insert to melt more quickly under the same conditions, which should be considered when addressing throat melting issues.

This Letter demonstrates the use of long-lifetime NO fluorescence for molecular tagging velocimetry (MTV) with (1 + 1) resonant-enhanced multiphoton ionization (REMPI) scheme, utilizing a single laser beam in a detonation-driven hypersonic shock tunnel. The Q1 branch of the NO A←X (0, 0) transition was excited using radiation near 226.256 nm. It was determined that (1 + 1) REMPI of NO generates long lifetime fluorescence, and this observation is consistent with the findings reported by Jiang et al. [Opt. Lett. 49, 1297–1300 (2024)] and Leonov et al. [Opt. Lett. 49, 426–429 (2024)]. Single-shot tagged lines at microsecond delay times were obtained in a Ma6.9 hypersonic freestream flow using a long focal length lens. The measured average velocity of 3477 m/s agrees well with the simulation result.

The flow near the stagnation streamline of a blunt body is often attracted and analyzed by using the approximation of local similarity, which reduces the equations of motion to a system of ordinary differential equations. To efficiently calculate the stagnation-streamline parameters in hypersonic magnetohydrodynamic (MHD) flows, an improved quasi-one-dimensional model for MHD flows is developed in the present paper. The Lorentz force is first incorporated into the original dimensionally reduced Navier–Stokes equations to compensate for its effect. Detailed comparisons about the shock standoff distance and the stagnation point heat flux are conducted with the two-dimensional Navier–Stokes calculations for flows around the orbital reentry experiment model, including gas flows in thermochemical nonequilibrium under different magnetic field strengths. Results show that the shock curvature should be considered in the quasi-one-dimensional model to prevent accuracy reduction due to the deviation from the local similarity assumption, particularly for hypersonic MHD flows, where the shock standoff distance will increase with larger magnetic strength. Then, the shock curvature parameter is introduced to compensate for the shock curvature effect. A good agreement between the improved quasi-one-dimensional and the two-dimensional full-field simulations is achieved, indicating that the proposed model enables an efficient and reliable evaluation of stagnation-streamline quantities under hypersonic MHD flows.