Abstract: When high-speed railway further speeds up, it will face huge energy consumption, aerodynamic noise and horizontal wind instability problems. Vacuum tube traffic can well solve the above operation problems. Based on the minimum space size, Knudsen number can be calculated. Based on Knudsen number, fluid flow state can be determined in the vacuum pipe. Based on the three-dimensional, unsteady and compression effect, vacuum aerodynamic calculation model is established, include train, station and pipeline, to analysis the relationship among train running speed, vacuum degree, blockage ratio, environment temperature and train aerodynamic drag. Studies show that train aerodynamic drag is parabolic incremental relationship with speed, linear incremental relationship with vacuum degree, linear incremental relationship with blockage ratio and linear incremental relationship with environmental temperature. The higher the train speed, the lower the vacuum degree, the higher the blockage ratio, the higher the environmental temperature, the higher the train aerodynamic drag. The research results provide theoretical basis for the value of Knudsen number feature length, the judgment of fluid flow state in vacuum pipeline, the numerical calculation of vacuum aerodynamics and the analysis of aerodynamic drag of vacuum pipeline traffic train.

Key words: aerodynamic drag, blockage ratio, environmental temperature, speed, vacuum degree, vacuum tube traffic