Thermal effects on the wall surfaces of transonic evacuated tube maglev transportation

Shock waves and expansion fan hierarchies in complex flows induced by transonic evacuated tube maglev transportation (ETMT) cause a unique thermal environment, which can increase the aerodynamic heating on the wall surfaces of the train and tube with the possibility of structural damage. In this study, the thermal effects on the wall surfaces of transonic ETMT were numerically investigated using a density-based computational fluid dynamics (CFD) solver. The results show different thermal effects for choked and unchoked flows in the tube. For the train, the extreme hot or cold environment, which is non-uniformly distributed on the surface, occurs more easily in the choked flow. For the tube, the instantaneous thermal impact is severe on the wall at supersonic speeds in the choked flow, reaching a maximum of 43.2 kW/m2 at Mach 1.5 with a blockage ratio of 0.2. The spectrum of the heat flux fluctuation on the tube wall is divided into the low-frequency band (main frequency) subjected to the normal or bow shock wave and secondary-frequency band induced by the downstream reflected shock trains. In addition, the amount of heat accumulated on the tube is insignificant owing to the interaction between the expansion fans and shock waves with alternating action on the boundary layer. Adoption of these findings, including the thermal control techniques and thermal-impact-resistant materials, for different ETMT systems can promote high-efficiency and low-redundancy designs of thermal protection systems.