Effect of acceleration and deceleration of a capsule train running at transonic speed on the flow and heat transfer in the tube

Acceleration and deceleration are required for train operation, and the flow field around the train shows strong unsteady characteristics during the acceleration and deceleration process. Some high speed related aerodynamic phenomena appear in the tube, such as shock waves, and significantly deteriorate the aerodynamic characteristics when the train speed reaches or exceeds the speed of sound. This study focuses on whether there are differences in aerodynamic effects when the train accelerates (decelerates) past the speed of sound, and the influence of different values of acceleration (deceleration) on the aerodynamic effects. The speed and motion of the train were controlled by a user-defined function and a sliding mesh technique in a commercial software of FLUENT, respectively. Aerodynamic heating phenomena and both the formation and the disappearance of shock waves were studied. The spatio-temporal distribution of the flow field parameters (temperature, pressure, etc.) was analyzed. The study found that acceleration and deceleration have different effects on aerodynamic drag, pressure, and temperature at different train speed intervals. With decreasing acceleration (deceleration) amplitudes, the maximum values of pressure and temperature and minimum pressure monitored at the tube wall increased, whereas the minimum temperature at the tube wall decreased.