Self-starting mechanism of a hyperloop pod under uniform acceleration: Theoretical and numerical analysis

Abstract

The self-starting of a hyperloop pod, characterized by the transition from a choked to an unchoked flow state during acceleration, can substantially reduce aerodynamic drag. This study develops a quasi-one-dimensional inviscid theoretical model to elucidate the underlying self-starting mechanism. The model describes the propagation of compression waves and the frontal normal shock wave (FNSW) ahead of the pod and provides analytical solutions for the coupled velocity, temperature, and pressure fields within the disturbed region. Furthermore, numerical simulations are conducted using a two-dimensional axisymmetric model with an overset mesh technique. The SST k–ω URANS-based numerical model is validated against wind tunnel experimental data and published three-dimensional simulation results. The present theoretical predictions are cross-validated against the numerical results, showing a maximum deviation of 2.8% for the FNSW. The results indicate that self-starting is governed primarily by the relative distance between the pod and the FNSW. Within the investigated range, acceleration mainly affects the rate of flow field and aerodynamic drag evolution but does not determine whether self-starting occurs. Under the uniform acceleration assumptions, self-starting is achieved only when the blockage ratio, defined as the maximum pod cross-sectional area divided by the tube cross-sectional area, is below 0.21. This conditional threshold provides guidance for pod–tube dimensional matching and aerodynamic safety.