Theoretical and numerical analysis of effects of sudden expansion and contraction on compressible flow phenomena in Hyperloop system
Jihoon Kim, Thi Thanh Giang Le, Minki Cho, Jaiyoung Ryu
Abstract
With rapid changes in lifestyle patterns and recent technological advancements, there is an increasing demand for efficient, convenient, and eco-friendly transportation systems. The Hyperloop system, which is a tube–train system, was introduced with the aim of catering to the demand for improved transportation facilities. The primary factors of the Hyperloop system such as the point of departure (pod), standstill, and transfer are directly dependent on the change in the cross-sectional area of the tube such as stations. In this study, the effects of sudden expansion and contraction were analyzed though numerical simulations with respect to the blockage ratio (BR), expansion ratio (ER), and contraction ratios (CR). Furthermore, the propagation Mach number and magnitude of pressure waves were predicted through theoretical consideration. Under sudden expansion and contraction of tube, the first leading shock wave (LSW1), reflected expansion wave (REW), second leading shock wave (LSW2), reflected shock wave (RSW), and third leading shock wave (LSW3) are generated in this system. The propagation Mach number and pressure magnitude of LSW1 increase with an increase in the BR. The Mach number of REW decreases with an increase in the BR. The propagation Mach number of LSW2 increases with the BR and with a decrease in the ER owing to the pressure behind the shock wave. The propagation Mach number of RSW decreases with an increase in the BR and with a decrease in the CR, and that of LSW3 increases with an increase in the BR and with a decrease in the CR. The drag coefficient decreases when REW reaches the pod because the expansion wave decreases the pressure of flow field. Owing to the similar minimum drag coefficient, the difference of drag coefficient increases with an increase in the BR. In this study, the predicted Mach number and pressure magnitude under quasi-one-dimensional assumption are in good agreement with the simulation results. Therefore, this study can aid the design of expanded and contracted zones considering the formation of the shock wave.