Numerical Analysis of Aerodynamic Characteristics of Hyperloop System

Abstract

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.

Mitigating the Piston Effect in High-Speed Hyperloop Transportation: A Study on the Use of Aerofoils

“…More recently, Oh et al [41] used a two-dimensional RANS model to study the aerodynamics of their Hyperloop pod. They observed the pressure build-up at the front of the pod at high speeds.…”

Computational fluid dynamics simulation of Hyperloop pod predicting laminar–turbulent transition

“…The design speed was Mach 0.3, although a transonic speed was also analyzed to evaluate the influence of the choke flow around the pod on the drag force. Oh et al [14] used CFD for an analysis of the aerodynamic characteristics of the Hyperloop system. In their study, large parametric studies were performed for the drag of the pod with different BRs, pod lengths, speeds and tube pressures.…”

“…However, mainly because of the short length of the Hyperloop pod, the Reynolds number is of the order of 10 6 for the subsonic case, and thus, the transition may play important role with respect to the drag. Nonetheless, the CFD studies mentioned above [10][11][12]14] assumed that the whole computational domain is fully turbulent and the laminar flow and the transition were neglected. Only Opgenoord and Caplan [13] paid attention to the transition.…”

Levitation Methods for Use in the Hyperloop High-Speed Transportation System

“…Since the first modern proposal in 2013, the concept of a Hyperloop system has morphed into many different variations, from small-scale prototypes fielded at the academic/industrial annual competition sponsored by SpaceX in its specially built 1.5km track (e.g., [3]) to the large-scale industrial prototypes that are expected to be operational within a decade (e.g., [4,5]). A number of studies examined the main issue of aerodynamic drag, and how it affects the Hyperloop pod motion inside the tube under different pressure conditions, using all possible approaches, from analytic calculations [6] to computations in two and three dimensions [7][8][9]. Reference 6 was one of the first studies to examine the pod aerodynamics and the specific issue of compressible flow around the Hyperloop system at high speeds using a one-dimensional analytic approach; its conclusion was somewhat negative, insofar as the study showcased the difficulty of achieving high pod speeds inside a tube, and brought forth the need for internal fans/compressors that would mitigate some of the challenges presented by aerodynamics.…”

“…It should be noted that this simple theory was inviscid, and therefore no drag was predicted for the flow around the pod. Recent CFD (computational fluid dynamics) work in two-and three-dimensional domains tackled the viscous flow surrounding the pod at high speeds and analyzed the wave pattern obtained in the flow [7][8][9]. These studies quantified the level of drag/friction incurred by the Hyperloop pod when traveling at various speeds at different ambient pressure conditions.…”