In future deep space exploration missions such as Mars sampling, manned landing on the moon, Jupiter system exploration, as the entry speed of the probe far exceeds the first cosmic velocity of the target planet, the system energy increases significantly. This leads to extreme flow and heat transfer phenomena accompanied by ultra-high temperature physical and chemical reactions, involving complex interactions between microscopic physical and chemical reactions and macroscopic flows, heat and mass transfer at the fluid-solid interface, and internal thermodynamic response of thermal protection materials. How to accurately predict such an extreme flow and heat transfer system with multi-phase, multi-scale, multi-process and strong coupling characteristics, so as to support the precise design of the probe for efficient kinetic energy dissipation and effective heat isolation, poses a severe challenge to fluid mechanics and related disciplines. This paper focuses on the extreme flow and heat transfer during planetary atmospheric entry, discusses and sorts out the key scientific problems in three aspects: ultra-high-speed flow, intense radiation heat transfer and ultra-high-temperature physical and chemical reactions, and prospects future research in this field.

The infrared thermal measurements and data analysis of a lifting-body model with gaps were carried out in the $\Phi 0.3\mathrm{m}$ hypersonic low-density wind tunnel of China Aerodynamics Research and Development Center. The experimental Mach number is 12, the total temperature is 668 K, the total pressure is 4.731 MPa, and the attack angles are 0° and 35°. Infrared thermograms of the model were obtained through experiments, and corresponding numerical simulation analysis was conducted. On this basis, the influence of selecting different frames of the infrared thermograms for data processing on the heat flux results was studied, and the heat flux increment caused by the gap interference was also analyzed. The results show that model jitter has a significant impact on the data processing after model release, thus it is recommended to select the infrared thermography results after the model reaches the stable state (about 1.2 s) in the data processing. More attention needs to be paid to the heat flux increase in the interference area of the T-shaped gaps, especially at 35° angle of attack, where the peak heat flux in the interference area of the gaps can reach more than 8 times that of the non-gap condition. The infrared thermal measurement data is in good agreement with the CFD results, and some difference only appears in a small peak interference area. In the next stage, more work needs to be carried out in the CFD model chamfering and the infrared thermal measurement scheme optimization.