Abstract: The overall flow induced by tube train and associated aerodynamic characteristics are investigated by theoretical analysis and quasi-one-dimensional numerical simulation. Three typical flow patterns, i.e. subsonic unchoked flow, choked flow and supersonic unchoked flow, are observed. The choked flow is generally accompanying with a precursor shock wave in front of the train and a secondary shock wave following the train. According to whether or not the secondary shock wave breaks away from the train, the choked flow may be further divided into two subcases. The aerodynamic drag on the train varies with the train speed and the trend differs by flow patterns. When the train speed is lower than the subsonic choking limit or higher than the supersonic choking limit, the flow is unchoked and the drag is small. When the train speed goes higher than the subsonic choking limit but under the secondary shock detaching limit, the flow becomes choked and the drag increases rapidly with the train speed. When the train speed exceeds the secondary shock detaching limit while lower than the supersonic choking limit, the flow remains choked and the drag increases mildly with the train speed. The drag coefficient peaks at the secondary shock detaching limit. Friction and heat transfer of the tube wall have a significant effect of attenuating the shock waves. But the overall influences of them on the transition limits of flow patterns and on the trend of drag are weak. Acceleration of train may influence the occurrence of two supersonic flow patterns. A smaller acceleration tends to delay the transition from choked flow to unchoked one. Numerical results indicates the transition of flow patterns during the acceleration is triggered by train overtaking the precursor shock wave.

Key words: tube train, aerodynamic characteristics, quasi-one-dimensional simulation, choked flow, secondary shock