Flow Characteristics and Aerodynamic Heating of Tube Trains in Choked/Unchoked Flow: A Numerical Study

Hyperloop has become one of the key reserve technologies for future high-speed rail transit. The gas in the tube is compressed and rubbed, leading to a strong aerodynamic heating effect. The research on the flow field characteristics and aerodynamic heating effect of hyperloop is in its infancy, and that on the flow field structure is lacking. In this study, the nozzle theory was used to make a preliminary judgment on the choked flow phenomenon in the hyperloop. Based on the flow results obtained under different working conditions, the identification basis of the choked flow phenomenon in the hyperloop was obtained. Furthermore, the effect of the choked/unchoked flow on the flow structure, temperature, and pressure distribution of the annular space in the tube was analyzed. Based on traditional high-speed railway aerodynamics, according to relevant theories and calculation in aerospace field, and combined with the model test data, the reliability verification analysis on the characteristics of the flow field are carried out. The structure of the flow filed in the tube can be divided into choked and unchoked. The judgment is dependent on whether the throat reaches the speed of sound. Under the choked flow, a normal shock wave is formed in front of the tube train. The temperature rise of the local flow field exceeds 50 K; the temperature rise of the stagnation region exceeds 88 K, and the pressure is approximately 1.7 times that of the initial pressure in the tube. When the flow is unchoked, differences arise in the distribution of the flow field corresponding to different incoming Mach numbers. When the incoming flow is supersonic, the flow field maintains a supersonic speed, and a bow-shaped shock wave is formed at the front of the tube train. Owing to the shock wave or expansion wave, the local flow field exhibits significant fluctuations in temperature and pressure. Conversely, when the incoming flow is subsonic, the flow field in the tube maintains a subsonic speed, and no shock wave structure is observed.