Theoretical and numerical studies on compressible flow around a subsonic evacuated tube train

Based on one-dimensional inviscid isentropic theory, the equations of flow parameters around a subsonic evacuated tube train are derived. In choked condition, the flow of tube throat reach the speed of sound and mass flow will not increase for a fixed upstream pressure and temperature. The flow around the subsonic evacuated tube train is a non-choked or a choked flow, under different operating speeds and blockage ratios. The flow parameters inside the tube can be solved. The theoretical results are compared and verified by numerical simulation using the overset mesh technique. The results show that the error between the theoretical and numerical results in the non-choked condition is within 2%. The maximum relative error in the choked state is 6.6%. When using the overset mesh technique for transient simulations, the initial speed of the train in the numerical simulation causes a higher intensity of shock and expansion waves inside the tube, but does not affect the results in other regions. In summary, the theoretical equation can predict the characteristics of compressible flow around a subsonic evacuated tube train.