Drag dependency aspects in Hyperloop aerodynamics

The Hyperloop system is promising a viable solution for fast, sustainable, and economic travel between cities. This paper investigates the challenging topic of Hyperloop aerodynamics via extensive numerical simulations. The study is divided based on the speed relative to the geometric Kantrowitz limit to manage the computational resources effectively. Below this limit, which marks the transition to choked flow, we conducted a cross-validation among an axisymmetric 2D model, a similar 3D geometry, and a realistic 3D geometry for blockage ratio 0.5 at several speeds. A definitive range for drag was determined, notably low absolute drag values were observed, and the 2D axisymmetric simplification was put into perspective. Above the choked flow condition, we undertook two resource-intensive simulations of the 2D setup, accelerating through several kilometers of tube. This methodology allowed us to shed light on the drag behavior that emerges under transient conditions. The existence of three regimes outlined by literature is corroborated by our study. Nevertheless, distinct variations emerge between the analyses, notably in the configuration of the shock wave structure, the linear increment of drag at a constant velocity, and the influence of the pod's acceleration profile in the flow structure. The study broadens the understanding of Hyperloop aerodynamics and offers realistic drag data for both choked and non-choked flow. • Drag was found to increase linearly at constant speed above choked flow. • A transient simulation setup is presented to analyze and visualize phenomena above choked flow. • The 2D axisymmetric simplification is put into perspective by comparison with a simulation using realistic 3D geometry. • The behavior of the first three aerodynamic regimes was confirmed and further described.