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The Hyperloop system is a new concept that allows a train to travel through a near-vacuum tunnel at transonic speeds. Aerodynamic drag is one of the most important factors in analyzing such systems. The blockage ratio (BR), pod speed/length, tube pressure, and temperature affect the aerodynamic drag, but the specific relationships between the drag and these parameters have not yet been comprehensively examined. In this study, we investigated the flow phenomena of a Hyperloop system, focusing on the effects of changes in the above parameters. Two-dimensional axisymmetric simulations were performed in a large parameter space covering various BR values (0.25, 0.36), pod lengths (10.75–86 m), pod speeds (50–350 m/s), tube pressures (~100–1000 Pa), and tube temperatures (275–325 K). As BR increased, the pressure drag was significantly affected. This is because of the smaller critical Mach number for a larger BR. As the pod length increased, the total drag and pressure drag did not change significantly, but there was a considerable influence on the friction drag. As the pod speed increased, strong shock waves occurred near the end of the pod. At this point, the flows around the pod were severely choked at both BR values, and the ratio of the pressure drag to the total drag converged to its saturation level. At tube pressures above 500 Pa, the friction drag increased significantly under the rapidly increased turbulence intensity near the pod surface. High tube temperatures increase the speed of sound, and this reduces the Mach number for the same pod speed, consequently delaying the onset of choking and reducing the aerodynamic drag. The results presented in this study are applicable to the fundamental design of the proposed Hyperloop system.

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In this study, the critical velocity was investigated with various aspect ratios (0.5, 0.667, 1.0, 1.5, 2.0) of the tunnel cross-section in tunnel fires. Reduced-scale experiments were carried out under the Froude scaling using ethanol pool fire. Temperatures were measured under the ceiling and vertical direction along the center of the tunnel. The effects of aspect ratio on critical velocity were analyzed from smoke movement. It has been found that the critical velocity increases with aspect ratio, where the aspect ratio is height/ width for a tunnel of rectangular cross-section. This study used new dimensionless velocity and dimensionless heat release rate parameters considering aspect ratio of the tunnel. The critical velocity varied with the one-third power of the heat release rate for under-medium fires. The results of this study are compared with other small-scale and full-scale experiments. A good agreement has been obtained.

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