Impact of the isentropic and Kantrowitz limits on the aerodynamics of an evacuated tube transportation system

In this work, the impact of the isentropic and Kantrowitz limits on the aerodynamic behavior of evacuated tube transportation (ETT) was numerically explored. Two tube train systems with different blockage ratios (beta), that is, beta = 0.09 and beta = 0.25, were employed for the comparative study of aerodynamic drag and flow structure. The results revealed three distinct aerodynamic behaviors, corresponding to the three speed regions separated by the two critical Mach numbers. Furthermore, the influence of head and tail lengths on drag reduction was investigated in these three speed ranges. An increase in head length appeared to be more sensitive to drag reduction at a speed of 600 m/s, while a long tail was found to induce a pronounced drag reduction at 200 m/s. In addition, the combined effect of the head and tail lengths on drag reduction was close to the superposition of their individual optimization effect. Based on the results, this study concludes that the individual designs of the head and tail of ETT systems may be rather demanding to achieve the desired optimization when considering distinct cruising speeds. Published under an exclusive license by AIP Publishing.