Influence of uniform atmospheric thermal conditions on the aerothermodynamics of transonic ETT

Evacuated Tube Transportation (ETT) is an emerging form of rail transit. The ultra-high-speed operation of vehicles inside the tubes induces severe aerodynamic heating effects, which threatens its safety and stable operations. Existing studies of aerodynamic heating on ETT have been conducted mainly under the adiabatic tube wall assumption, thermally isolating it from the external environment. The differences in the aerodynamic thermal environment of the ETT under mixed and adiabatic tube wall boundaries, and the influence of uniform atmospheric thermal conditions on the aerothermodynamics of the transonic ETT were investigated in this work. The results reveal that an adiabatic tube wall boundary significantly overestimates the internal aerodynamic heating, particularly the wall temperature in the high-temperature zone and the temperature gradients on both the tube wall and the vehicle surface. However, under the two thermal boundaries, the main flow characteristics and aerodynamic loads remain nearly unchanged. Within the BR of 0.1225–0.3403, as the vehicle speed increases from 0.8 Ma to 1.2 Ma, the average surface temperature rises by 32.41 K–44.36 K. The vehicle body can continuously dissipate heat via radiation to the tube wall, thereby lowering its temperature. External air temperature and solar radiation are the dominant factors affecting the wall thermal effects, whereas wind speed plays a much weaker role, especially in the wake zone. Under the high-conductivity tube wall, enhancing the outward thermal radiation capacity and reducing the solar absorptivity can effectively improve the aerodynamic thermal environment of the ETT.